Food Gardening

Natives vs. non-natives – good or bad for pollinators?

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A large olive green and dark orange moth with fast beating hummingbird type wings using its proboscis to feed on a pueple flower.
Native pollinator, Clearwing Hummingbird Moth, visiting non-native Verbena bonariensis, Purpletop vervain. Photo: M. Talabac, UMD Extension

As a biologist who works on pollination, two of the top questions I receive on a regular basis are what to plant to support pollinators, and whether non-natives are bad for pollinators. Although I can state a number of relatively easy-to-grow plants that are both good for supporting pollinators in our area (past blog articles: Want flowers next year? Pollinator plants to plant this fall, What should I plant to help pollinators? and Helping pollinators in small green spaces are some ideas), it is really hard to give a hard answer based on research knowledge to the second question. In today’s article, I decided to try to explain why this is so, and still try to answer that question. Spoiler alert: my answer is basically an “it depends” with some big caveats. Keep reading to see what I mean.

Concepts meet reality

One of the characteristics of scientific knowledge is that it accumulates, and that knowledge we collect can eventually be used to make predictions about what one may expect to observe under new conditions. These predictions are of course not necessarily correct all the time, but their accuracy is expected to increase with the amount of knowledge that we have about the processes we are seeking to predict. As a scientific field, biology has indeed accumulated a lot of knowledge, which allows us to make some pretty logical predictions about the potential effect of non-native plants on pollinators. Let’s go over some of those predictions.

As I mentioned in a previous post, “What are local ecotype plants and why do they matter to pollinators?“, the interactions we observe today between plants and their pollinators are the result of millions of years of (co)evolution, which has modulated the “matching” of needs of the two parts of the interaction. This means that evolution led to species that interact to be generally well-adapted to each other. For example, species that have been interacting for a long time at a given place (as is the case of species that are native to a place) tend to temporally match better with each other; bees that use certain plants tend to be active when those plants flower, and plants that need certain bees tend to flower when those bees are active. This means that it is plausible that if those plants or bees are not available at a certain time point, they will not be able to survive properly because their needed partner is not around. In the context of exotic plants, it is possible that the fact that they are exotic makes them poor pollinator plants, since they are more likely to not be “attuned” to the temporal needs of the local species.

A black white and yellow striped caterpillar feeding on the leaves of a plant with slender leaves and orange clustered flowers.
Native Monarach butterfly caterpillar feeding on Aesclepias tuberosa, Butterfly weed, one of the milkdweed host plants. Photo: Crista Carignan, UMD Extension

From a different perspective, plants and pollinators have an interaction that is based on the consumption of floral rewards (pollen, nectar, etc.) by the pollinator (and in some cases, such as that of moths and butterflies, the consumption of other plant tissue in their larval stages). Those rewards, however, are not chemically identical across plants, meaning that each plant species, genus or family will tend to have rewards that contain chemical compounds specific to them, and to which the pollinators that consume them are adapted, leading to different levels of specialization. The practical consequence of this is that not all pollinators visit all plants, but rather that certain pollinators will only visit the plants that offer rewards they can physiologically consume and digest. These adaptations to deal with certain chemical compounds evolve over a long time, meaning that it is more likely that species native to the same area will be able to effectively display them, simply because those species have been exposed to those compounds for longer and are thus more likely to be adapted to them.

Given all of this knowledge, it is expected that species that have been evolving with each other over long periods of time – such as species native to the same region – would also be more beneficial to the pollination partners than species that are not native to the same region. And indeed, there are some studies that show that some non-native plant species are not chemically or temporally accessible to some bee species, leading to certain bee species avoiding them altogether because they cannot manage the chemical compounds they carry. That said, those studies are rarely counted, not because people do not want to take them on, but because testing such ideas on many species across the world requires a lot of funding, time, access to appropriate sites, and technical skill… all of which makes the studies extremely hard to run.

So, are non-natives good or bad for pollinators?

Despite the large technical, financial and logistical complexities of testing the points I noted above specifically, some studies have tried to evaluate the effect of non-natives on pollination interactions and the parts involved through the study of spaces that already carry different levels of natives and non-natives. These studies confirm some of the predictions but also bring a more nuanced light to the topic… which points to the need for more studies and my “it depends” type of answer to the question. So, let me tell you what these studies tend to show.

A relevant study on this is one in which gardens that had different levels of ground cover by native and non-native species were studied in terms of their floral visitation. In that study, they measured A LOT of gardens and followed floral visitation of all the plants present throughout a whole season. What they saw was that generally pollinators tended to be more abundant when most natives were flowering, but that later in the season non-natives could provide resources to pollinators that were still around but had no native plants to visit, because those were not flowering anymore (or not yet). Based on that study, one would suggest that planting natives is indeed good (that leads to the most visits by pollinators) but that displaying non-natives that flower later in the season (especially when natives that flower at that time of the season are not available) can help support some pollinators during those times because they compensate for the lack of native floral resources available to pollinators. This said, that study was geographically restricted (a small region of Germany), included only urban gardens, could not manipulate the composition of the plant choice (this was on gardens that were already established based on the homeowners’ choices) and was done through one season only. The authors also recognized that many times the non-natives were of the same family of a native plant, meaning that perhaps the pollinators were already slightly pre-adapted to their chemistries, and that the results would thus be different if no native related plants had been present. Also, they warned about the use of non-natives that could have potential for invasiveness. (Exotic garden plants partly substitute for native plants as resources for pollinators when native plants become seasonally scarce)

Only a few studies were done after this one, but they found slightly different results. For example, a study done on flower plantings in Paris over two seasons found that native plants indeed support more diverse, abundant, and specialized pollination interactions, but that the non-natives used in those sites appeared to support more generalist interactions than the native species. This would suggest that native plants appear to be positioned particularly well to increase pollinator diversity and to support *specialized* pollinators that would otherwise not be supported at all by the non-native plants.

Finally, another study (from the USA) that looked not so much at the plants but at the pollinators, found that non-native non-honeybee bees tended to clearly prefer non-native plants over natives, meaning that those plants would tend to provide support especially to non-native bees, and thus appear to assist in some ways the survival of non-native bees that are in some cases competing for resources and displacing native bee species. (Native and exotic plants play different roles in urban pollination networks across seasons)

This is complicated! What do I do with this information?

Generally, I would interpret all of this as pointing to:

  • Native plants should be preferred when possible because they do indeed support larger and more complex sets of pollination interactions.
  • If they are non-invasive, one can maybe consider planting non-natives, especially if plants of the same family or genus are already native to the region. However, it is always important to ask oneself why one wants to absolutely do this.
  • Non-natives can help support pollinators during the “summer dearth”, when few natives are available… although one can also try to increase the frequency of natives that do flower during those times.

By Anahí Espíndola, Associate Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Second Chance Peppers

EricaLeave a comment

Last month I blogged about giving up on plants. This month, I’m encouraging you to give some of them a second chance.

A caserole dish show a pile of large red peppers cut in half holding a mix of beef, corn, rice and other ingredients.
Dinner from my bountiful peppers! Photo: Erica Smith

Specifically, I’m talking about plants (vegetables or other) that you tried and failed with, and suspect that the failure may have been due to planting them in the wrong place, caring for them poorly, or maybe the happenstance of getting a bad seed or seedling. Sometimes our best-laid plans just don’t work out for, you know, reasons.

About five years ago I got some seed for Giant Aconcagua peppers and grew them in two subsequent years. Here’s what I said in this blog at the time, in an early October post:

I tried again with the Aconcagua sweet peppers, and had the same problems as before: a) the seedlings are slow-growing and weak; b) the peppers take forever to turn. I did get a couple of red ones, and the pale green ones are quite tasty and nice and big. I may try one more time, getting the seeds going at the end of January or the beginning of February, to see if I can produce seedlings rugged enough to go into the ground in May. 

I didn’t try again, though, because I thought these peppers were fussy and not worth the effort. This year, for whatever reason, I decided to give it another go. Wow, what a difference. I didn’t bother to start them super-early, and I’m glad I didn’t, because the seedlings started in mid-March grew as fast as all the other peppers, though they still began life with slightly paler leaves and a floppier structure. But they took off, getting to three feet high far earlier than they’d done before, and this time producing heavily with ripening in August rather than September or October.

A close up view of the pepper plants with a leaf and a number of red or turning red peppers hangin down through the interior of the plant.
Not the best photo, but you get the idea or how many peppers are on this plant. Photo: Erica Smith

And these are BIG peppers.

A large reddish orange pepper lays on a cutting board next to a ruler showing 9 inches long.
Photo: Erica Smith

They are not all 9 inches long, but most are close. They are more similar to a stretched-out bell pepper than a thin-walled Italian frying type, so great for all kinds of dishes.

I recommend these if you want a big pepper in your life. They absolutely must be supported, which you can do with the kind of medium-sized wire tomato cage that isn’t big enough for most tomatoes. And keep up with pruning or tying up branches! I lost a whole branch of green peppers in a thunderstorm because the weight got to be too much for the plant.

Why didn’t they work for me as well before? It could have been a set of weak seeds that didn’t have the best genetics for quick growth. Or I put the plants in spots that didn’t get enough sun or water, or had too much weed competition. Or a combination of those factors.

Seed catalogs use language that’s designed to make you jump at a particular plant variety, and we all know that, so given a poor performance, we say it was all hype, and we should never have believed the glowing description. But sometimes there’s truth behind the sales pitch, and we just need a second chance to find it.

Now, if I’d bought another seed packet and had the same poor results? Likely I’d have given up. Some plants just don’t work in a particular climate or setting, and enough trial and error lets us discover that. But one failure is not enough to declare the experiment over.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Invasive Ornamentals and Sterile Varieties

Maryland Grows4 Comments

When it comes to landscaping, a huge decision-making point is what we find visually pleasing… and often what pleases us visually ends up being something we are not very used to seeing, meaning that we pick plants that seem more exotic to us so we can marvel at their surprising (to us) beauty. This is all good and nice, but the problem appears when we realize that many of those plants appear exotic to us because they are exotic to the region we live in! This means that if we select them to plant in our landscapes, we are actually adding to our environment species that are not necessarily native to where we live… which can have pretty drastic consequences. In today’s post, I want to talk about a potential solution that has fairly recently been proposed to the use of such plants: sterile varieties.

What’s the deal with exotic plants?

Although not all exotic plants will have negative effects on our environment, some of them do. Those that do are considered invasive species, and they can create a lot of trouble in our local ecosystems. Invasive plants tend to grow faster than other native plants, often overrunning the spaces they grow in, spreading very quickly, and eventually “choking” or outcompeting local species, which end up dying out and/or becoming unable to survive in the presence of the invasive plant. Some good examples of this behavior of invasive plants in Maryland are the Chinese and Japanese Wisteria vines and the English Ivy, all of which effectively cover trees and can eventually choke and pull them down to their death.

View of a forest with vines covering the tree trunks up into the canopy.
In the Eastern USA, English Ivy does effectively take over forests. Photo: L. J. Mehrhoff.

In Maryland, this issue has been recognized not just by ecologists, but also by lawmakers, who have started to regulate the selling of specific species to properly support the protection (and recovery) of our local plant communities. Among the most recent additions to these regulations are the ban on selling several bamboo species, English Ivy, exotic Wisterias, and several very invasive grasses (among other species). You can check the most up-to-date list of these species at the Maryland Dept. of Ag. website: Maryland Prohibited Invasive Plant Law and Regulations. The Maryland Department of Natural Resources also hosts a website with a lot of information about exotic species (plants and others): Invasive and Exotic Species in Maryland

So what to do if we love the plants but do not want them to spread?

Ideally, if we do not want to harm local habitats, the best decision is to refrain from planting invasive species, because they are REALLY hard to properly control and prevent their spread (especially when there is bird-mediated fruit dispersal or stolon-mediated dispersal).

The forest in spring with many mature trees and Barberry invading the understory and dominating as the ground cover
Barrberry dominating the understory in a wooded setting. Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Bright red berries the shape of water drops hang along barberry branch.
Barberry shrubs produce many berries that birds and wildlife eat then distrubute. Photo: Chris Evans, University of Illinois, Bugwood.org

An alternative, however, is the selection of varieties that are unable to spread because they are sterile or do not have proper structures to do so. These are varieties that exist for some ornamentals/exotics, and that are in some cases exempted from the regulations that I was mentioning above. Some examples are non-invasive bamboo varieties, some Berberis cultivars (e.g., varieties “Lemon Glow”, “Crimson Cutie”), and even some almost-sterile Buddleja cultivars (e.g., “Flutterby”, “Lo and Behold” varieties developed by several University programs). A note on some of these cultivars is that although some of them are labeled “sterile”, they may or may not be fully sterile. Some of them have indeed been shown to, in some cases, produce some fertile offspring (although way fewer than their fertile counterparts!).

A green field with a forest line in the background. Purple wisteria vines are growing up many trees and shrubs, toppling one over.
Invasive Wisteria invades forests, vining themselves onto trees, pulling them down and eventually outcompeting and often killing them. Photo: M. Bakacs.

How to go about these decisions?

Generally, when considering exotic ornamentals for our green spaces, it is worth making it a practice of first informing ourselves about their potential for invasiveness. Then, if the potential is there, another good practice is to look for potential alternatives (e.g., do we really need to plant that specific plant?, are there less-harmful varieties?, are there native alternatives that can be planted instead?, can we properly contain the plant if it spreads?).

To make these decisions, a good tool to consider is the NC Extension Gardener toolkit, where species and varieties are listed and can be filtered out by (among other traits) their potential for invasiveness/weediness. The Maryland Invasive Species Council has also put together a list of species that have invasiveness potential (independently of regulations) and are thus of concern. A new tool from the University of Maryland Extension Maryland Native Plants Project can help you search and filter for native plants, so you can potentially choose a native plant which will suit your needs and benefit our eco-system: Maryland Native Plant Finder tool.

By Anahí Espíndola, Associate Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Giving Up On Plants; or, When to Commit Plant Murder

Erica2 Comments

I think we’ve all been there. Everything else in the vegetable garden is going well, growing as it should, producing bountifully, getting the better of challenges. And then there’s the one plant that just… isn’t. (Or more than one that just aren’t.) Maybe, though, given a little more time, a little more fertilizer, a little more effort, a little more love… it might pull through? Or is it taking up space for no reason? Worse, is keeping it around bad for your more successful plants?

When, in fact, is it the right time to commit plant murder?

I can’t help joking, but of course we all hate killing plants that we’ve tried hard to nurture, maybe even growing them from a tiny seed. But let’s face it, there’s only so much space in a garden, and the season will be over soon. We don’t want to waste the time and square feet that we have. Most of the plants in an edible garden are annuals, and with these we need to make decisions soon. With perennials, maybe you can wait until next year to see if conditions improve.

How do you figure out when and if you should pull a plant out of the garden? Well, it’s like a detective story in reverse; first, you need to be an investigator, and then a potential killer. Find out what’s wrong with the plant; assess how bad the problem is and what the consequences might be; and then make a decision based on the facts.

The HGIC website is a good place to start. If the plant in question is a vegetable, I suggest starting with the Vegetables Grown in Maryland page, select your vegetable, and visit the “Growing ___ in a Home Garden” article. From there, you can explore the list of potential problems. If you can’t figure it out from there, or from more searching online, you can contact the Ask Extension team, or ask your county’s Master Gardeners.

The problems you might encounter with plants include:

PESTS

Pest problems are often fixable. Follow the advice given at HGIC or on other regional Extension websites, and you are likely to be able to control the pests sufficiently to get a crop. However, there are a few instances where giving up on the plant is a better option.

  • The pest has killed the plant or come close to killing it. For example, squash vine borer can take out a squash plant in days, and if you don’t remove the pest in time, or it has destroyed most of the main stem, you will not be able to revive the plant. Flea beetles can eat most of the foliage of young eggplants, to the point where they can’t survive. But don’t jump to the conclusion that a few holes mean a devastating invasion.
  • The pests keep coming back even when you remove them. This happens often in community garden situations or when you have close neighbors growing the same plants. Maybe you can work together to get rid of the pests, but if that’s not an option, you might consider switching to a less susceptible crop.
  • There is a solution, but you can’t implement it right now. This is particularly true of animal pests—maybe you need to fix a fence or fill a hole, and it’s best done in the off-season. Or you have overplanted a bed, making it difficult to reach plants to remove pests. The easiest fix may be to remove the temptation and limit the pest’s options in the process.
A leaf of a squash plant with holes and yellowing from squash bug feeding.
Squash bug damage in plants I couldn’t get to because I overplanted my small garden. Photo by Erica Smith

Remember that not dealing with insect pests as soon as possible means that they are able to complete their life cycle and make more pests! If you do remove a plant that is infested, try putting it in a black plastic trash bag and leaving it out in the sun until the pests are dead. That way, you haven’t just chased them off to attack another plant. You can then put the bag in the trash or even add the contents to your compost if the plant isn’t also diseased. Speaking of which…

DISEASES

If you suspect a plant disease, diagnose it and read up on its prognosis. Does it kill a plant fast, or is it slow-working? How lethal is it and how fast does it spread? Again, it’s likely you can keep plants going for a while, for example with a common fungal disease like early blight on tomatoes, but there are cases where plant removal is advisable. If you do pull plants, put them in the trash rather than adding the debris to your compost.

  • Diseases that spread quickly. If you see the disease spreading to other plants, and it can’t be stopped by removing affected foliage and other plant parts, you may need to pull the plants that are diseased. This is especially true in truly destructive diseases like late blight (luckily, this is uncommon in Maryland!), but also with more common issues like bacterial leaf spot, which has devastated some of my recent pepper crops. Remember, most diseases are specific to particular species or families, so you don’t need to pull out your whole garden because one type of plant is affected.
  • Diseases that will prevent a plant from producing. Examples include bacterial wilt that kills a cucumber overnight (easy call), or mosaic virus that lets a squash plant continue to grow but will kill it before it has any viable fruit (harder to make the decision to pull). In perennial plants such as fruit trees, you may lose a crop one year but not the next; on the other hand, if the disease comes back for several years running despite treatment, why are you still trying? (It took me a couple years of fire blight on quince to decide I wasn’t meant to grow it.)
  • Multiple factors, including disease. A disease alone might not be enough to make you decide to pull a plant, but if it’s also battling pests or drought, or producing very little for some other reason, it might not be worth keeping.
A red bell pepper with rotten spots on the skin.
This pepper damage was likely caused by bacterial leaf spot. Not worth keeping the plants going if the result looks like this! Photo by Erica Smith

OTHER

  • Failure to thrive. This is a generic term for “just not cutting it”: looking puny and sad. Maybe the seed you grew this plant from was the worst one in the packet; maybe it got stressed from being in a pot too long; maybe the soil conditions in that particular spot are poor; maybe we’ve had crazy weather and the plant just can’t cope. Some TLC and fertilizer may help, but not always.
  • Bolting. Cool-weather crops often last into the summer, but there’s always a point when they want to go to flower, and no amount of pruning will stop it.
  • Failure to produce correctly. Maybe the plant looks healthy but it isn’t making what it’s supposed to make. Root vegetables that don’t make roots; beans that don’t bean; broccoli that won’t head up. A little extra time and some fertilizer may help, but possibly not. Pull the plant; do a soil test and plan an appropriate fertilizer regimen next year; look at conditions generally (enough sun? enough water?).
  • Need the space for something else. In a small garden, we sometimes have to make choices about what hangs in there and what gets ousted. If you want to grow kale and there is nowhere else to put it but where the tomato plant is covered with early blight and producing many fewer fruits, it may be time for the tomato plant to go.
A weak looking pepper plant with only 1 small fruit starting to grow.
This fish pepper has been looking sad all season. Might be a soil issue, or stress due to root crowding in the pot. Or something else. I still don’t want to pull it out, so I gave it some fertilizer and a pep talk. Photo by Erica Smith

In general, remember that failures are a learning experience! Sometimes we learn about a fundamental flaw in our garden or in our practice; sometimes we learn that a particular plant isn’t for us (but give it another try first!); sometimes we can just chalk up failure to a bad year or one fixable mistake. Pulling a plant is also an opportunity to put another plant in its place. (Probably not one of the same species, because the problem may affect it too.) Succession planting is made easier by thoughtful but relatively quick decision-making; get out that sick squash and you may still have time to put some bush beans in, or to get the space ready for fall planting.

And as gardeners, we always continue to hope things will be better next time!

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

The Need to Weed

Erica2 Comments

I recently got back from a 10-day trip away from home, and had to brace myself before I approached my community garden plot. I hoped there wouldn’t be pests or diseases to deal with. I was pretty sure the tomatoes would have escaped the bounds of their cages. But the one thing I knew I’d encounter was WEEDS.

A close up of various weeds in a garden setting where you can see some leaves of corn poking through.
Weeds including wood sorrel and unwanted grasses in a bed growing corn and onions.
Large okra leaves in a raised bed with various weeds underneath them.
SO MANY WEEDS in the okra bed at the Derwood Demo Garden

It was not as bad as I’d feared, but I still had to deal with a lot of unwanted plants, which is basically what weeds are. All plants have their place, but that often isn’t in our vegetable gardens, flower beds, or landscapes. I often hear from people that we should let certain weeds grow, because they are part of the ecosystem, because they support pollinators, or because they have other uses, such as being edible. In some very specific cases, these are good arguments. If I have a native plant come up in the middle of a veggie bed, I might let it grow, or more likely I would transplant it to another location in my yard (or into the row of native flowering plants I’ve established in my community garden plot). If it’s a non-native invasive that is about to produce around a thousand seeds that will spread the plant all over my yard or the community garden, I’m going to yank it, even if it has pretty flowers that the bees like. I might also let an edible weed like purslane grow, if I’m in the mood to harvest it and use it, but I’d try to contain it before it spreads too far.

Here are the main reasons that you should remove weeds from your vegetable garden, even if it’s a lot of work and you don’t feel like it:

  • Competition. In some environments, growing lots of plants close together is beneficial. Even vegetable gardens can benefit from close planting in some circumstances, to shade the soil or to confuse herbaceous insects. But weeds are weeds because they are survivors, and they tend toward domination. They will swallow up your desirable plants in no time, suck up all the water and nutrients, and provide you with nothing.
  • Reproduction. Weeds spread like crazy either via seed or by suckering roots. If you have one weed this year, next year you will have hundreds. This is bad enough in your own backyard, but if you have close neighbors, or if you’re in a community garden, you are not going to be popular. (In a community garden, you may be ousted before next year, depending on the rules and how they’re enforced.)
  • Pests and diseases. Each weed is part of a particular plant family, often the same family as some vegetable you’re trying to grow. It may harbor some of the same pests and diseases as that vegetable. Guess which plant is going to shake off the problems faster, and which one will tenderly succumb?
  • Ticks. Love to hide in weed patches and hitch a ride as you pass through on your way to the squash. There might also be other critters lurking in out-of-control weed jungles, such as snakes (good to have around, but startling), or entire rabbit families in a nest. Just to name a few. Plant a native hedgerow and let them live there, not in your tomato bed.
  • Aesthetics. I put this last for a reason, but even if you personally don’t long for a tidy garden, keep in mind that vegetable gardening as a pursuit sometimes gets bad-mouthed for being “messy” and any actually messy gardens can contribute to a stereotype. HOAs that forbid front yard veggies, neighbors that complain about completely hypothetical rats, they all learned their prejudices somewhere. Don’t let it be your garden. We all want more homegrown produce in the world, not less.

So get out there and pull the weeds! And then, think about how to stop them from growing in the first place. Here are some things you can do this summer and beyond:

  • Mulch. Put something over your soil, preferably an organic mulch like shredded leaves, straw, or dried grass clippings. You can even use weeds as mulch if they don’t have seeds on them. Compost can be a mulch if you are sure it’s been heated enough to kill weed seeds. Synthetic mulches like black plastic or weed barrier fabric are also an alternative, though they won’t add organic matter to your soil. When you disturb the soil to put in plants or seeds, try to cover it again to prevent the germination of weed seeds that have been brought to the surface. (Obviously, don’t put a thick layer of mulch over the seeds you just planted.) Mulch is also great at keeping the soil from losing moisture in the heat, and maintaining it at an even temperature. And it may help prevent fungal spores from splashing up from the soil onto your plants.
  • Learn to ID weeds. Know your enemy! As you pull a weed, use a plant ID app or other source to identify it. After some time and work, you’ll know the common ones and you can learn about how and when they reproduce. Do I have to get the whole root out (yes, for perennials) or can I just remove the top of the plant before it goes to seed (usually, for annuals)? How early in the year do I have to get out there to start pulling weeds? (Earlier than you think, alas.) The other advantage to knowing weeds is that you’re less likely to mistake them for the plants you want to grow, and vice versa. Close observation works equally well for identifying veggie seedlings. Be an informed gardener!
  • Think about growing in containers. Refreshing the potting mix every year will definitely mean fewer weeds.
  • Speaking of which… think about containing or restricting plants that are desirable but act like weeds. Various mints and their relatives, shiso/perilla, leaf fennel, some amaranths… I have personal knowledge of how badly these spread, and I’m sure every gardener has a similar list. Whether you trap the roots in a pot (on a paved surface, in the case of mints) or make very sure to cut off the tops before the seeds go flying, it’s a responsible thing to do and will spare you a big surprise come the next growing season.

And lastly, be patient. Weed seeds lurk in the soil for many years, so they probably will keep coming back. There will be setbacks. But eventually, things will get easier and more enjoyable, and (mostly) weed-free.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Small but mighty. The amazing ground-nesting bee!

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The summer is almost here, and if you are like me, you have already been outside and seen a bunch of tiny bees digging, digging, digging, and buzzing around flowers. Who are these little ladies? And what on earth (pun intended) are they doing? In today’s blog, I want to explain a bit about these super powerhouses, how they do what they do, and point to some of these cool bees that we can find right here in Maryland and our general region.

What are ground-nesting bees?

As its name indicates, ground-nesting bees are bees that nest in the ground, mostly by digging their nests. Ground-nesting bees are found in several families of bees, and being a soil nester/digger is actually one of the most common nesting strategies among solitary bees. In these bees, once the female finds a good nesting site, she starts excavating it to create an underground nest, which often has several brood cells, in which the larvae develop. These nests are usually found in spaces where the vegetation is sparse or the soil bare, and can sometimes be built along with other nests of the same species, leading to communal nesting areas. It is because of this preference for relatively open ground that it is often recommended that at least some uncovered ground is left in our green spaces, which helps provide habitat for their establishment.

A tiny bee is seen crawling out of a mound of soil on the ground.
Ground-nesting bee coming out of her nest. Photo: Colleen (CC0).

How do ground nesters build their nests?

As good miners or soil diggers, ground-nesting bees also have specific behavioral and morphological traits that make them good at what they do. Bees that excavate have modified leg structures that allow them to easily move within tunnels, strong mandibles that they use to actually dig the cavity, and modified extremities of the abdomen (the pygidial plate) that function as sorts of trowels and allow them to pack soil on the walls of the cavity they are digging.

Along with having the right tools of the trade, these bees are also selective of the type of soil they use to build their nests. Most ground-nesting bees prefer soils that are not too compacted, with at least some sand content, which makes them easier to dig through. This means that it is more likely that we will find these bees in rockier/sandier soils than in super clay-y ones. As a matter of fact, many ground-nesting bees are associated with dune nesting, and because dunes are often endangered habitats (because they are often disturbed/destroyed by human activities), many sand-nesting specialists end up becoming endangered as well. And as a fun fact about soil choice, bee experts think that because finding “good soil” is so important for the survival of these bees, bees tend to become associated with specific spots for nesting, with the nesting site becoming a sort of “family place”, where several generations of females from the same family line come back to nest over the years/generations.

A close up of the pygidial plant which is a small darker triangular structure at the tip of the bee's abdomen.
The pygidial plate is a structure present at the tip of the abdomen of ground-nesting bees that functions as a trowel. Photo: MN Native Bees.

Because digging through the soil with their mandibles (and sometimes their legs) is hard work, bees usually tend to choose the best timing to start their digging. In fact, the hardest part of the soil to dig through for a bee is the surface, which is often the most compacted. For this reason, bees tend to start digging after the soil has become moist (e.g., after rains). Incredibly, some ground-digging bees are even able to add, if needed, secretions or even nectar to humidify and loosen the soil! Once the bee has started her excavation, she continues digging deeper and bringing soil out of the construction area, which leads to all sorts of “mounts” being built around the nest entrance and sometimes chimney-looking structures.

What are some ground nesters from Maryland?

Andrena vicina – The neighborly mining bee

a close up of a bee gathering pollen from white flowers
Andrena vicina. Photo: K. P. McFarland (CC0).

This Andreniid is relatively large (about 1- 1.5 cm), present in North America and common in the Eastern USA. This species received that cute name because it is one of those that builds communal nesting areas (“neighborhoods”). In Maryland, the species is active right now (~June/July) and is generally seen visiting many native plants and crops. In particular, this is one of the known visitors of, among other plants, Rhododendron and Azaleas, several heather family plants (like Vaccinium, Kalmia), as well as several rose family plants (Prunus, Rubus).

Augochlorella aurata – Golden sweat bee

a tiny metallic green sweat beed in the center of a yellow flower

Augochlorella aurata. Photo: C. Martin (CC0).

This is a species in the Halictid family, and is called a sweat bee because it is often found collecting sweat (for water and salts). This is one of those tiny bees that you may find landing on you on a hot day, really committed to not letting go of your skin! This particular bee is relatively easy to recognize because it is small, metallic-looking, with beautiful green/golden iridescence. This bee is not fully solitary and is a species recognized to display primitive eusociality (for example, honey bees are true eusocials). In this species, there is a queen that starts a nest, and across the season, generations of first infertile and later fertile workers are produced. By the end of the season, the fertile workers are inseminated and disperse to overwinter. This bee species is pretty generalist in its choice of plants, known as a pollinator of many crops (e.g., apples, tomatoes, watermelon) as well as native plants.

By Anahí Espíndola, Associate Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Dealing with Pest Issues in Container Vegetable Gardening

Erica3 Comments
Close up of a gey squirrel eating potted plant sitting ontop of a brick wall.
Wildlife can be cute, but also destructive! Photo via Adobe Stock

You’re happily growing lettuce in a salad table, watching the little seedlings get bigger, and then one day half of them have been dug up and tossed aside. Or you’re about to harvest your kale and then realize it’s full of holes and little green caterpillars. Or your eggplant leaves are suddenly nothing but lace. Maybe someone is stealing your tomatoes, or—more insultingly—taking a bite out of each of them. Or maybe everything is just… GONE.

Pest issues are not unique to container gardening, of course—all veggie gardeners deal with them. But just as containers have their pluses and minuses in every aspect of food growing, they sometimes provide specific challenges and benefits when it comes to dealing with pests – whether insect or animal.

By the way—let’s acknowledge here that the creatures we’re talking about are just trying to get along and feed themselves. They don’t know that they’re putting us to extra trouble (even if it really seems like squirrels in particular are just trolling us). It would be great if we could jall just get along without harming each other. So the proposed solutions below don’t go as far as hurting or killing anything (if you want to use pesticides against insects, that is up to you, though please be sure to carefully follow the label instructions). These methods all follow four principles: Location, Exclusion, Deterrence, and Distraction.

PART ONE: INSECTS

Here’s a typical scenario from Home and Garden Information Center’s Emily Clark-Waterson:

I planted kale in a flower box in the spring in a new self-watering flower box container, hanging off my balcony railing. It grew beautifully and I was able to clip young leaves and let them keep growing until the summer weather got too hot. I planted it again in late August for a fall harvest, except this time I started to notice some leaf damage and found a type of Imported Cabbageworm. These moved fast and left little to be harvested. They like to hide along the midribs. Lesson learned: Always cover your brassicas with insect netting or floating row cover to help prevent this. A small piece of tulle from a craft store works well, or you can purchase various-sized mesh bags to put over containers. I won’t be making that mistake again.

Kale leaves with large holes and small green caterpillars resting on the leaves
How many cabbageworms can you find? Photo: Emily Clark-Waterson
A small green caterpillar on the underside of a kale leaf.
They really can be camouflaged in the leaves. Photo: Emily Clark-Waterson
A larger green caterpillar rests along the midrib of a kale leaf with large holes in it.
This one has eaten well! Photo: Emily Clark-Waterson
Two containers with vegetable plants sit along a white picket fence. Each container we had a tomato cage and piece of tulle draped over it
Prepared for pests this year with tomato cages and tulle held together with clothes pins. Photo Emily Clark-Waterson

This is a great example of Exclusion. In fact, covering plants with materials like this solves the majority of insect problems—and it’s so much easier and cheaper in a container than covering a long row in an in-ground vegetable garden. Here are some other examples of plants in the brassica family being covered to protect them:

Fine mesh instect netting stretched over plsatic hoops that are over a container of greens.
Insect mesh and hoops over Asian greens. Photo: Lily Bruch
a container on the edge of a raised bed garden with a sheer cloth covering some greens growing. The cloth is draped over and tied around the conatiner with a black string.
Floating row cover over brassica plants keeps caterpillars and other pests away. Photo: Robin Ritterhoff

Plant covers work against other insects as well, for example, to keep flea beetles off of eggplants. But in this case, growing in containers provides another advantage, one of Location. Erica Smith has had success over the years by growing eggplant in containers on her deck, which keeps them well away from the flea beetles in the soil below. MG Robin Ritterhoff also uses this method, making sure to replace at least the top third of the potting soil every year in case beetles are lurking. But MG Lily Bruch says her eggplants still get eaten despite growing on a deck, so she uses row cover and also plants marigolds in hopes of Deterrence. Sometimes strong-scented plants either confuse or annoy insects and keep them away from your vegetables. It’s worth trying, since flowers also bring in much-wanted pollinators and other beneficial insects.

And what if the insect eating your plant is actually beneficial? MG Mary Anne Normile writes:

[It’s a tough call] when Eastern black swallowtail caterpillars feed on container parsley. I love the butterflies, but the caterpillars can denude a parsley plant in short order. No good solution unless you have another desirable (to the caterpillars) plant to relocate them to, except possibly to have a fresh batch of parsley seedlings on hand to plant for the short period after the caterpillars stop feeding and the end of the growing season.

If you have room, you can plant extra herbs in the parsley family, such as dill and fennel, which the swallowtail caterpillars will also enjoy. (Also make sure to have lots of nectar-producing flowers for the adult butterflies.) You could also cover up a few of the parsley plants to keep them just for you.

When pest problems arise in container plants, make sure you address them quickly, because it’s easy to lose your entire crop in very little time.

PART TWO: ANIMALS

(Yes, insects are animals; let’s not be pedantic.)

Erica here:

This is a photo of the gate to my old vegetable garden:

A half eaten tomator sits ontop of a wooden railing of a gate.

This is a typical squirrel move. Didn’t even eat the whole tomato and left it in an obvious place just to taunt me. Photo: Erica Smith

And this year, I have a squirrel who loves Swiss chard:

Squirrel seen through a window screen sitting on the edge of a planter on a deck eating lettuce.
It ate every single seedling out of the deck planter, leaving the lettuce alone, and then climbed into my garden and snacked on the beet leaves. Oh well, no Beta vulgaris for me this year! Photo: Erica Smith

Mary Anne writes:

I have had squirrels … dig up freshly planted basil in containers. They seem to love fresh soil. They don’t eat the basil, they just dig up the plants and sometimes toss them out of the container. I replant them and sprinkle the surface of the soil liberally with cayenne (the cheapest stuff, not Penzey’s), repeated after a rain, and that deters them. Once the basil plants are large enough, the squirrels don’t bother them.

Squirrels do instinctively dig in fresh soil, sometimes burying nuts, but other times looking for food or following up an interesting smell. Lily reports that they dig up her lettuce seedlings; her solution is to cover the container with a metal grid or chicken wire.

Planter box on a deck with lettuce plants growing in it. Metal chicken wire is formed over the top.
Chicken wire to exclude squirrels Photo: Lily Bruch
Salad greens grow up through wire mesh in a planter box on a deck.
Metal wire grid to exclude digging squirrels Photo: Lily Bruch
A white flower box with salad greens sits on the edge of a flagstone path. A pink netting food tents resting rests on top of the container blocking wildlife from digging.
Picnic food tents resting over a container is enough to keep the squirrels from digging up new lettuce seedlings. Photo: Emily Clark- Waterson

Lest you think this section of the blog is all about squirrels, they are, in fact, one of the worst pests for container gardeners (and veggie gardeners in general). They can climb anything, and they eat a wide variety of foods. And they are determined. They may be the hardest animal to stop once they start bothering your garden. Except possibly for raccoons—and former MG Nancy Moses had both of them!

Here’s Nancy describing the year she planted vegetables in containers on her second-story deck—in a yard surrounded by a six-foot fence but that backs up to woods.

The squirrels and raccoons climbed over our chain link fence, up the 13 steps to the deck, taking over the territory as their own.  The resulting poop was unpleasant!  The light-weight, conniving, hungry squirrels politely climbed over the netting held up with metal stakes in each tomato-growing pot; and the raccoons knocked over the pots and anything else in their way toward achieving their goal of mass destruction and hunger gratification. 

Nancy says that after that, “You could say that I quit; but I view it now as having just politely surrendered.” And honestly, how can you blame her? She tried the principles of Location—putting the pots up on a high deck—and Exclusion. Maybe the netting could have covered the plants more thoroughly, but the raccoons still would have knocked the pots over. The only real solution would have been Total Exclusion, meaning a fence that completely surrounded and covered the pots, which does not lead to enjoyment of the deck by humans.

So back to those principles. Location often works (in less extreme circumstances) by keeping plants in pots up high where some animals won’t venture. Most deer (we can never say all) won’t climb up steps and some won’t even venture close to a human home. Rabbits are short and don’t climb, so higher planters are unreachable. A balcony location keeps even groundhogs off, though probably not squirrels and certainly not birds.

Exclusion with row cover or netting can keep some less determined animals and birds away. Fences are another solution—you can fence off part of a deck or patio, or put your containers inside a fence in the yard (or use them as part of your regular veggie garden). Again, if you have serious squirrel, raccoon, or bird issues, only a garden enclosure with a roof will help.

Deterrence can mean using strong-scented plants to warn away animals that don’t enjoy those smells. It’s no guarantee, but maybe will stop the casual visitor.

Colorful wooden planters stacked agains an outside side to a building with herbs, annuals, and strawberries.
Colorful planters hold strawberry plants up high, and a “citronella plant” scented geranium as one of the strongly-scented deterrent plants to offend visiting herbivores. Photo: Erica Smith

In extreme cases, you can revert to growing only these sorts of plants. Herbs like rosemary and thyme, onions and their relatives, and hot peppers may be unattractive to animals.

There are other methods of deterrence if you want to try automatic water sprayers, constant noise, or bird scarers of various types. Avoid sprays that are meant to repel deer if they contain any ingredients you wouldn’t want to consume.

Distraction means giving our animal friends something else to think about. Some garden writers advise providing an alternate source of food, such as edible plants closer to the animal’s habitat, but be wary of bringing in an entire extended family that will reach your closer-to-home plants eventually. Also, be sure to keep compost containers secure if they hold food scraps, and keep fallen produce cleaned up. (We have not talked about rats so far in this post, and let’s not start now.) But do make sure animals and birds have a water source they can visit—sometimes they are eating your vegetables because they’re thirsty.

If possible, try to provide natural sources of food by planting shrubs and trees (preferably native to your region) that grow seeds, nuts and fruits. If you don’t have room yourself, use our resources to learn about native plants and try to convince neighbors or anyone else who controls plantings in your neighborhood to grow them.

Dealing with pests can be challenging, but it feels great when you rise to the challenge! Growing in containers can sometimes help you combat pests, such as when you can easily cover a pot or place it somewhere the pests can’t get to. And if you need to take a season off to regroup, it’s so much simpler to just empty the pots and put them away, rather than having to close down a big garden. Do some research, find some solutions, and come back refreshed to try again!

Share your struggles and triumphs in the comments—and best wishes!!

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.