Scary plants earn Halloween points. Some plants are downright scary. Since Halloween is around the corner, I thought it might be fun to discuss a few.
Raise your hand if you love weeds. Okay, weeds are my nemesis. Yours too, I bet. If you’ve ever wrangled with mile-a-minute you’ve probably dreamed of this vine engulfing your house, your car, your dog. Ditto with bindweed, bermudagrass, and other brats. But armed with a little knowledge and persistence, you can get the upper hand. There’s a good weed ID guide on our website with photos and management tips.
Mile-a-minute weed spreads aggressively by seeds spread by birds. Photo credit: Leslie Mehrhoff, University of Connecticut; Bugwood.org
Much scarier are invasive plants. These plants are obnoxious spreaders that threaten ecosystems. English ivy, garlic mustard, and others bully out native plants that we – and wildlife – need. Lest you think I’m exaggerating, look at photos of garlic mustard blanketing forest floors or trees smothered in English ivy. These plants are a serious threat and need to be banished. Learn more at our invasive plants page.
Garlic mustard sneaking under a pine tree.An infestation of English ivy in a forest. Photo credit: Leslie Mehrhoff, University of Connecticut; Bugwood.org
Have you ever noticed a garden center plant labeled as “vigorous?” Beware. That could be nursery-speak for “spreads like wildfire.” These vigorous plants are often beautiful and can be tamed, but it’s best to go into any relationship informed. I call them my beautiful monsters, plants I can’t be without but need to manage carefully.
Mint will spread like mad so always, always contain it in a pot. Brazilian verbena (Verbena bonariensis) will drop seed like crazy. Deadhead it – or at least some of it – before it goes to seed. Obedient plant (Physostegia virginiana) is anything but obedient. Dig out its sneaky underground rhizomes where you don’t want it or enjoy it in others’ gardens. Yes, it’s a native, but it is a serious spreader. Forewarned is forearmed.
Obedient plant is anything but obedient, spreading quickly.
Another scary plant is poison ivy. I itch at the mention of its name. The merest brush of a leaf is enough to make me blister. First things first when tackling poison ivy. Cover any part of you that might come into contact with the plant. And consider having on hand a product that neutralizes the oils that cause itching. Remove small seedlings by hand. Sever vines growing up trees. Treat when you must, following the guidelines in our fact sheet. Ironically, we’re the only species for whom poison ivy is a problem. It’s a native plant with berries that form late to feed many forms of wildlife. It only irritates our skin and sensibilities.
Less scary are the plants in our gardens with a white latex sap such as milkweed, balloon flower (Platycodon grandifloras), and spurge (Euphorbia species). The sap can cause minor skin irritations, more of an annoyance than a threat. The same is true with juniper rash, the red dots you get from pruning junipers. Wear gloves to protect your hands from itchy spots and dots.
I hope I haven’t scared you too much. Most plants are quite harmless and a delight to both tend and behold. Into every garden a few itches, weed witches and vexing plants must grow.
By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. Read more by Annette.
Incised fumewort (Corydalis incisa). Photo: Miri Talabac, University of Maryland Extension
Have you seen incised fumewort (Corydalis incisa)? This frilly, little wildflower is surprisingly invasive. Originally from East Asia, this species has been spreading southward along the I-95 corridor from New York since 2005. The first iNaturalist observations of incised fumewort in Maryland were made in the spring of 2018. As of this writing, Maryland contains 259 Research Grade observations. Many gardeners report that the seeds must have been present in potted plants or mulch that they purchased. In our parks, incised fumewort quickly outcompetes native spring wildflowers, and particularly dramatic declines in Virginia bluebells have been observed in the Bull Run floodplain (Northern Virginia).
Incised fumewort came into bloom in mid-March this year and normally continues blooming until early April. Seeds ripen within three weeks of blooming. Ripe seeds are explosively dispersed up to 10 feet away from their parent plants. They may also be dispersed by flowing water, tracked mud. Some reports indicate they are dispersed by ants.
Gardeners and landscape maintenance professionals tell us that manual control is unreliable at best. In some cases, even very persistent, frequent episodes of manual control have failed. Chemical control is more effective, but has its own challenges, such as unintended damage to nearby native plants.
In either case, it helps to understand that the species is biennial. The flowers of second-year plants are easy to see, but seedlings are inconspicuous. If management only targets flowering plants, that can be a viable strategy. But for folks who didn’t realize there were also seedlings present, it can be shocking to see that despite all your hard work there are even more flowering plants the next year. This gives the impression that management is failing, which may or may not be true. My casual observation is that seedlings (dicotyledons present) germinate in both spring and fall. I suppose the spring germinators go dormant for the summer and re-emerge in fall while the other seeds are germinating. The resulting rosettes are fully evergreen. The rosettes have a small, soil-colored tuber. For those of you doing manual control, make sure to remove it.
You can help by reporting this plant when you see it. You can do that quickly and easily using the iNaturalist app. Just point, click, and upload. There is even a space there where you can leave us some notes. Your observation will contribute to a publicly available map that is used by many land management agencies and their volunteers (Weed Warriors) to prevent new infestations from becoming established.
By Sara Tangren, Ph.D., Environmental Program Coordinator, National Capital PRISM, Metropolitan Washington Council of Governments. This article was published originally in the University of Maryland Extension IPM Alert, March 22, 2024.
Invasive Asian honeysuckle (Lonicera sp.). Photo: Rachel J. Rhodes, UME
Eliminating unwanted plants is often one of the most challenging chores that gardeners face. Not introducing invasive plants is the fastest and most economical way to make a positive impact, as once invasive plants are introduced to your garden, it can take many years to eliminate these invaders from your landscape.
Invasive plants propagate and spread by many different methods, which makes controlling them difficult and different for each species. Please learn feasible control tactics provided by land-grant universities or Extension factsheets/webpages before starting. Fact-based research is the absolute first step in getting ahead of plant invaders. Often invasive plants cannot be controlled 100% in just one growing season, but preventing the plant from making seeds or spreading is better than doing nothing at all.
Questions to guide your research:
Get proper plant identification! Use Ask Extension, Local Extension Professionals, and Master Gardener Plant Clinics. Smartphone plant ID apps can give you some idea, but you should follow up and confirm the correct identification. Apps may be limited by photo quality and geographic area.
Is the plant a woody perennial, herbaceous perennial, or annual?
Has the plant been a problem for several years in your landscape, or is it a relatively new concern?
You must know how it is reproducing/spreading in your particular situation. For example, if the plant reproduces from stem/root cuttings, the last action you want to take is to mow/weed-eat/till the roots, which would cause the plant to produce hundreds of new plants.
If controlling 100% is not a feasible option, determine how you can prevent the plants from spreading or allowing them to get stronger.
If you have an invasive plant in your landscape and you really enjoy it, learn how to prevent it from spreading. For example, the spread of some plants can be prevented by removing flowers/viable seeds so that wildlife does not consume and spread them, or so that wind/rain does not blow away the seeds.
Always include “MD Extension” with internet search engines to be sure that identification and control tactics specific to Maryland are being filtered to the top of your results.
Three basic control options are categorized below.
Mechanical control
Mechanical control options are often the first step that people take in controlling unwanted plants; however, these are by far the most physically demanding and often lead to a high level of site disturbance. Examples of mechanical control are:
Pulling and digging.
Suffocation or smothering with landscape fabric, mulch, cardboard, multiple layers of newspaper, anything to block the sunlight and prevent the plant from growing.
Solarization: laying plastic over the plants to “cook” live plants and viable seeds with the heat that builds up underneath.
Cutting, repeated cutting, or mowing in hopes of weakening stored nutrients so that the plants can not regenerate. This is also done to remove the flowering/seed structures.
Biological control
Biological control options utilize something else that is alive—insects, fungi, grazing livestock animals, etc. More and more of these options are being explored; however, sometimes the control agent may be 100% specific to the problem plant, or sometimes it may be able to feed on other plants too, which is the case with the Kudzu bug.
Kudzu bug (Megacopta cribraria). Photo: Russ Ottens, University of Georgia, Bugwood.org
Chemical control through herbicide application
Foliar Applications
Cut Stem or “Hack and Squirt” Treatments
Herbicides are a management tool that may be considered when other control measures have not been successful. Sometimes this control option provides the least amount of physical labor, low soil disturbance, and is more effective than other options. Pesticides can be overwhelming and intimidating, with misinformation and inaccurate “facts” being shared. If you would like to learn more about “mode of action” and how different herbicides are classified, check out this Herbicide Mode of Action link from Purdue.
A few questions that might help you determine if it’s time to explore herbicides as an option.
Have you tried mechanical or physical control options without success?
Would one application of herbicide save the soil on the site from being excavated, dug, or destroyed?
Always use the most appropriate chemical control option by finding the plant that you want to control on the product label and following the application instructions carefully.
Remember, with any pesticide (herbicide, insecticide, fungicide, rodenticide, etc.), the Label is the LAW! This is true even with organic pesticides.
The Environmental Protection Agency (EPA) is charged with approving, analyzing, and standing behind pesticides. Before approval, these herbicides are tested and labeled for use with specific instructions to minimize negative risk to yourself and the environment. Always use in accordance with the label and keep good records.
Herbicides that are commercially available to purchase have been tested to know the recommended rates and residual activity in soils and on micro/macro organisms. There are a lot of unknowns with homemade solutions, so homemade “remedies” are not recommended.
Invasive winged burning bush (Euonymus alatus). Photo: Rachel J. Rhodes, UME
Disposal of invasive plants
The last step in controlling invasive plants is proper disposal. Leftover plant materials can lead to potential accidental new infestations.
Proper disposal guidance:
Burn– If your county/city allows the burning of yard debris, be sure to follow all safety regulations and restrictions and do not breathe the smoke.
Pile– Fully dead/dried woody material that does not have seeds/fruits and is not covered in soil (which could allow it to sprout roots) can provide great nesting and shelter sites for wildlife- Read “The Value of a Pile of Sticks in Your Yard or Landscape”.
Dry or expose debris to intense heat– place debris in a black trash bag and let it “cook” for several weeks out in the hot sun, this will ensure that there are no viable seeds in the debris and all moisture is removed so that nothing can sprout. You can then add this to compost piles or dispose of it as you would “normal” landscape trimmings.
Check with your county/city government to find out if invasive plants should go in your yard waste or regular trash.
English ivy (Hedera helix)Heavenly bamboo (Nandina domestica)Yellow flag iris (Iris pseudacorus)
Let the particular plant that you are trying to control guide your management plan, and research the plant before you begin. Start control strategies on a small scale to see what works best and remember that many of the characteristics that led people to begin planting these invasives are the exact reasons that they are hard to control— some examples: wildlife resistance, good at spreading, breaking dormancy before natives early in the season. Also, keep in mind that many invasive species are a long-term fight and will require perseverance and, for best results, will require the use of different control tactics.
Lastly, once you successfully control the problem species, have a clear plan of what you will do with this space in your landscape. Installing new plants or keeping the area mulched will help prevent soil erosion or new infestations of weeds. Here is a list of recommended native plants for Maryland.
Everyone can help in the fight against invasive plants! Check the University of Maryland Extension website for an Introduction to Invasive Plants in Maryland and more information on how to reduce them. The absolute best way is to just never plant or introduce them into your landscape.
By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.
Speedwell is a winter annual weed. It will end its life cycle and die naturally once we have consistently warm temperatures. Photo: G. Rinehart
The warmer-than-normal weather during February had many people thinking about an early start to lawn and garden season. However, as temperatures have dropped and been below normal for much of March, it looks like we may have a couple more weeks before lawns really start growing. Lawn growth and crabgrass emergence are related to soil temperature, which is slower to change than the air temperature. While I have heard reports of soil temperatures topping out in the mid-50s for a day or two, it’s important to remember that in order to germinate crabgrass needs soil temperatures around 53-55⁰ F sustained for 5 days. These two things lead to a few questions, particularly pertinent this year when February felt like March and now March feels like late February.
Should I fertilize my lawn now?
While the legal window for applying fertilizer to lawns in Maryland began on March 1, that doesn’t necessarily mean you should fertilize your lawn just yet. Unless the grass is actively growing (which is dependent on warmer soil temperatures) it likely won’t take up and use the fertilizer—so you are better off waiting until the lawn is actively growing. Temperatures consistently around 60 and enough growth to warrant a second mowing are pretty good indicators of this. Keep in mind that if you fertilized your lawn in the fall you can probably wait until after the “flush of growth” in the spring (usually April/early May) and then schedule your spring fertilizer application for after that “flush” and leading into summer—usually around mid-late May. If you didn’t fertilize last fall it is tempting to try to “jump-start” the lawn in early spring with a fertilizer application, but hold off until the soil temperatures are consistently warmer and highs are around 58-60⁰ F on a regular basis.
Should I apply crabgrass pre-emergent now?
I would wait until soil temperatures are 53-55⁰ F sustained for 5 days. Keep in mind that your best defense against crabgrass is a dense turf that crowds out crabgrass seedlings. So, if you have good turf density and mow at 3” or higher, your overall crabgrass pressure should be lower anyway. The typical recommendation is to wait until the forsythia is “half green-half gold” (or even a little earlier), but with the warm February we had, that indicator may or may not be as accurate this year. You can check soil temperatures for your location at the following website: https://www.greencastonline.com/tools/soil-temperature.
Is there harm in applying crabgrass pre-emergent too early?
Probably not, unless it’s applied several weeks early and the product starts to break down before crabgrass even starts germinating. If you want to maximize the period of time your crabgrass application is effective, wait until when conditions are conducive to crabgrass germination and then apply it.
Roughstalk bluegrass (Poa trivialis) is a cool-season weed that shows up in early spring. If you only have a few patches, you can dig them out by hand (including the roots) and overseed to fill in the bare spots. Photo: G. Rinehart
On another note, this is now the time of year when many winter weeds become more noticeable as they are likely producing flowers and setting seeds. While you can apply selective products to control these weeds, remember that these winter annuals like chickweed, purple deadnettle, speedwell, henbit, etc. are almost at the end of their lives and will die naturally once we have consistently warm temperatures. Another weed often noticed this time of year is the grassy weed called roughstalk bluegrass (Poa trivialis). Seeds of this grass are often a contaminant in turfgrass seed mixes (the cheaper the seed, the more likely you will have weed seeds) and this grass starts growing much earlier than tall fescue. As the temperatures warm, it is not as aggressive and noticeable. There are few selective control products that are labeled for roughstalk bluegrass and they tend to be restricted to professional sites and/or are expensive. If you only have a few patches in your lawn, digging these out (including the roots) and then re-seeding the spot with a soil-tall fescue mix is the best control approach for most homeowners.
In the bottom two middle squares of my raised bed garden, the spinach and leaf lettuce is growing from last month, but now it appears like there are some unwanted plants as well — weeds! In just a few short weeks, our garden has been overtaken by weeds. The weed seeds came from the topsoil I purchased. Weeds are a problem when you have a garden of any size, unless you use new, sterile, soilless growing media each season. Knowing what you planted will really be important so you can be on the lookout for the seedlings, and remove just the weeds.
Seedling leaves (cotyledons) often look completely different from the first true leaves that come out later. One characteristic that can help you in figuring out if you have a weed or a plant you want to grow is by looking at the number of leaves that sprout from the seed. If the plant has one seedling leaf, it is called a monocot (monocotyledon). This includes plants like onions, corn, and grasses. If the plant has two seedling leaves at germination, it is called a dicot (dicotyledons) and includes plants like tomatoes, beans, potatoes, spinach, and lettuce. Dicots are sometimes referred to as broadleaf plants. Many times selective herbicides work on either monocots or dicots but not both types of plants; that’s what determines which plant will be killed by the herbicide or which will be resistant. Non-selective herbicides will kill both monocot and dicot plants.
Sometimes people get really upset when I call a plant a “weed.” Please remember that many plants can be designated as weeds. The simple definition is “a plant growing where it is not wanted.” So even though weeds can have desirable characteristics, when it is a plant growing where it is not wanted, it is a weed. Weeds compete for sunshine, water, space, and nutrients in the garden, and some can be hosts for diseases and pests.
As with most gardening tasks, addressing the problem early and often is the best advice. Being able to identify weeds when they are small is one of the skills that I continue to hone each growing season and it takes practice and time. Knowing what you planted and where you planted it is the first step in knowing what may or may not be growing. Virginia Tech has a nice identification guide that lets you answer questions about the specimen and points you to a possible answer.
Left: Grass seedling, an example of a monocot. Right: Ragweed seedling, an example of dicot.
Examples of dicot weeds. Left: Lambsquarter (larger and smaller stages). Right: Smartweed (see the thumbprint in the center of the leaves).
I will be using mechanical control methods (hand pulling or a small hand shovel to remove the weeds) because it’s such a small area.
In our commercial high tunnel operation, we use a physical barrier as our first line of defense in weed control. Wind can cause hardships with keeping landscape fabric held in place, but we use 6-8’’ long landscape pins to hold it down.
The left photo shows damage as it appeared the morning after the frost. Right: shows what the damage looks like a week later. It hasn’t killed the plants, but they will be set back from the frost.
We have had some very chilly night temperatures which is not too uncommon here in the mountains. Our expected frost-free date is June 5th, so I’m looking forward to putting in some warm season vegetables in the coming weeks — tomatoes, peppers, green beans, and maybe a summer squash are on our list.
Weeded garden bed
By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.
In a mid-March post, I wrote about the advantages of using heavy-duty weed barrier fabric to smother weeds and create a no-till plant bed. In mid-June, I found myself with two beds that were starting to get weedy. The winter cover crop that had protected the soil was quickly decomposing and crabgrass and broadleaf weeds were emerging.
Rapidly growing weeds are quickly brought under control with weed barrier fabric.
I threw on 3-ft. wide strips of the weed barrier material and after five days of very hot weather all of the vegetation was dead. Continue reading →
Q: I think I might have giant hogweed on my property, or maybe it is poison hemlock. How can I tell for sure?
A: Giant hogweed (Heracleummantegazzianum) was found recently in Clarke County, Virginia, and it has raised awareness and concern about the plant – and rightfully so. The plant produces toxic sap that can cause very severe skin inflammation. We have received a lot of questions about it lately.
Poison hemlock Photo: E. Nibali
What you have here is NOT giant hogweed. It is poison hemlock(Coniummaculatum), which is much more common. The ferny foliage makes it possible to distinguish it from giant hogweed.
