Pollination of Vegetable Crops in a Warming Climate

Pollination is the movement of pollen from male to female flower parts of sexually reproducing plants. It is often accomplished by wind and insects and results in the development of some type of fruit containing seeds for the species’ continuation. Farmers and gardeners in the mid-Atlantic are finding that high day and evening temperatures can cause vegetable plants to drop flowers and small fruits or produce deformed and under-sized fruits. This  problem has been observed in crops like bean, tomato, and pepper (mostly self-fertile; individual flowers can pollinate themselves), and in crops like squash and pumpkin (require cross-pollination between flowers).

How do high temperatures affect pollination?

All fruiting plants have an optimal temperature range for the pollination/fertilization process. High temperatures can reduce pollen production, prevent anthers from releasing pollen, kill pollen outright, and interfere with the pollen tubes that serve as conduits for uniting sperm cells and eggs (fertilization) inside undeveloped seeds (ovules). High temperatures can even injure flowers before they open. Night temperatures are increasing at a faster rate than day temperatures as a result of climate change, and seem to be most responsible for these pollination problems.

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Improve Soil Health for a Climate-Resilient Garden

Soils, plants, and animals are highly interdependent. Soils support and feed microbes and plants which feed animals. Dead plants and soil critters replenish the soils’ organic matter and nutrient supply, completing the cycle. We know that healthy soils produce healthy plants. Many experts believe that improving soil health is the most important thing we can do to make our farms and gardens more climate-resilient. 

Why are soils so important in dealing with climate change? 

  • They store huge amounts of carbon in the form of carbon dioxide (CO2) and organic matter, all of the living, dead, and decomposing plants, microbes, and animals that live in soil. Carbon dioxide is the primary greenhouse gas that is warming the planet. Deforestation, the removal of wetlands and peatlands, and soil tillage cause the release of huge amounts of CO2. Warmer temperatures cause more rapid organic matter decomposition and turnover, especially if soils are tilled and uncovered.
  • Climate change is causing mid-Atlantic weather to be warmer and wetter with more extreme weather events, including periodic drought. This increases the risk of soil erosion and nutrient run-off from intense rainfall, and the risk of plant stress from excessively wet or dry soils. 
Soil from a landscaping project that moved off-site in 2018. Maryland averaged 73 inches of rain that year!
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Heat-tolerant vegetable crops and cultivars for the changing climate

Our food-growing spaces allow us to grow healthy produce, connect with Nature, and hopefully save money. They are also a solid response to climate change and COVID.

My blog articles this year will be about climate-resilient food gardening. Each month I’ll address one or more aspects of how climate change is affecting our food gardens and changes we can make to reduce global warming and ensure a future of healthy harvests.

HGIC has a new Climate-Resilient Gardening section (thanks to Christa Carignan!) where you’ll find more information on these topics. We plan to continually update content and add new pages. And please check out the University of Maryland Extension’s new Healthy Garden, Healthy You project that connects food gardening and human health.

This first installment includes an overview of how our mid-Atlantic climate is changing and a look at heat-tolerant crops and cultivars. Future articles will explore low-dig soil prep, composting food scraps, peat alternatives, heat stress in plants, reducing plastics, and “hardening” our garden spaces.

Resiliency is mentioned a lot with respect to climate change. A climate-resilient garden can both withstand and recover from warmer, more extreme weather. Resiliency can also mean transforming how we grow food by creating and sharing a community knowledgebase of new ideas and techniques.

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Fighting CO2 on a Balcony

It’s well known that atmospheric carbon dioxide (CO2) is one of the leading causes of climate change and that plants play a role in mitigating its impact by taking in carbon dioxide and releasing oxygen. But did you know that even the smallest gardens can make a difference? Container gardens can be effective ways for adding plants to the ecosystem, nurturing pollinators and other beneficial insects, and even providing food for your table.

A container garden with mixed perennials and annuals provides beauty, food, and habitat. Photo: Pat Wilson

High above Columbia’s Wilde Lake at the Residences at Vantage Point, long-time gardener Barbara Schuyler continues the gardening that was her passion when she and her wife Pat Wilson lived on a rural property. More than 90 containers of shrubs, annuals, perennials, and vegetables grace two balconies that face west and south.

Barbara’s approach to container gardening

Shrubs and perennials comprise a significant part of the garden. Hardy perennials winter over and are especially effective at drawing down carbon dioxide. Some of the perennials, like the orange butterfly milkweed (Asclepias tuberosa) pictured below, are natives. Native plants are well-suited to our climate, require less care than imported species, and support native insects. Barbara’s native plants also include lots of Rudbeckia, some Echinacea, and several Heuchera

orange and blue flowers planted in a container garden
Native butterfly milkweed (orange flowers) combines beautifully with the blue-theme flowers. Photo: Barbara Schuyler

In addition, each year Barbara and Pat decide on a theme and collect annual seeds to plant when the temperature warms up each spring. Last year, the blue flower theme provided a consistent backdrop for the foliage and flowers of other plants.

She uses regular potting soil and each spring spreads the old soil on a tarp to remove roots and debris and returns it to the pots with a portion of fresh potting soil added.

Her collection of containers is eclectic and includes salad tables for vegetables, wine barrels, ceramic and plastic pots. A container exchange in the building helps many patio gardeners find pots that meet specific size and decorative needs. Reusing and sharing materials can help reduce CO2 associated with buying and shipping new products. She also tried felt bags but was not pleased with the results.

spray handle attached to kitchen sink
Photo: Christine Hipple

Watering 90 containers with a watering can during dry spells would be a major challenge, so Barbara purchased a garden hose sink adapter to allow her to connect a lightweight flexible hose to the kitchen sink.  

One big advantage of balcony gardens is that deer can’t get to them, though she has seen a squirrel or two.


Visiting her garden every morning is a joy in itself. It provides Barbara the opportunity to be present with her plants, be aware of their needs, and appreciate what they offer throughout the seasons.

Even at this extreme height, pollinators are attracted to and supported by the garden. Three species of bees, several types of moths, and even a few monarchs have been spotted.

Lettuce and arugula do well in pots, and along with cherry tomatoes provide healthy super-local produce — yet another reduction in their carbon footprint. One lesson Barbara’s learned about cherry tomatoes is not to crowd them. Plant just one to a large pot and prune assertively to be sure the energy goes into making tomatoes rather than excess foliage and that there’s sufficient air circulation.

cherry tomatoes ripening
Growing some food at home is fun and helps reduce the carbon footprint of food transport. Photo: Barbara Schuyler

While there’s some level of physical work involved, container gardening is within the reach of nearly everyone – no matter your available space, skill level, physical abilities, or budget. Start small. Share stories, plants, and pots with other gardeners, and enjoy the benefits for yourself, your community, and the planet!

Are you taking any steps in your garden to help mitigate and adapt to climate change? Have a story to share? Let us know! Leave a comment or contact us.

By Christine Hipple, University of Maryland Extension Master Gardener, Howard County, Maryland

Starting a compost pile and planting cover crops – winding down the vegetable garden for the year

After a fun year of building support structures and growing really long squash, it was time to wind down the garden. Our first baby was born (thank you, thank you), and we had no further bandwidth or ambition to continue with cool-season crops, so I decided to pack up the support gear, rip out the remaining plants that were producing but slowing down, start a compost pile with the remains, and plant cover crops in the beds.

Packing it up

My big trellis used for the Tromboncino squash and the one made from part of a fencing panel used for tomatoes both folded up and packed away nicely in this outdoor storage area attached to my house. I’m happy with my designs, as I didn’t want permanent structures out in the garden getting weathered, and I didn’t want them to take up a lot of space in storage. These will be easy to set up next year again. The only thing I will do differently in the future is to use something stronger than twine to string on the trellis and hold up tomatoes with tomato clips. A lot of the twine that was under pressure from crops eventually snapped and needed replacing.

Rip it, chop it, bin it

We were going to have such a volume of garden waste this year, I decided to start a compost bin. This should give us a head start on the new layer of compost (previously all store-bought) we add to the raised beds each year. Pretty much all we have to do is throw this stuff in a bin and wait, as we are doing passive composting that is slow but requires very little attention.

I bought a cheap compost bin online; this one is just a sheet of black plastic with holes that you form into a vertical cylinder and throw your stuff into.

I ripped up our squash, watermelon, and tomato plants, wheelbarrowed ’em over to the compost bin in our back yard, stabbed at the pile with a shovel and buzzed it with my string trimmer for a while to chop it up a bit. Then I shoveled it all into the bin, attempting to mix up the types of plants in there somewhat uniformly.

Once leaves fall, I’ll drop some leaves that have been shredded by the mower into there as well.

I know you can drop food waste like fruit and vegetable scraps into compost, but I’m not sure we are going bother making the trip from the kitchen to backyard with a couple banana peels since that’s just not a lot of volume to make a difference for our intended purpose.

We will need to turn the pile a couple times in the next year to aid decomposition, but other than that, this is hands off. I’m looking forward to seeing what we get at the beginning of next growing season to start our summer vegetable garden again.

Cover crops for our raised bed garden to make it through the winter

I know it is good to protect my soil from erosion and add a layer of compostable material on the top over the winter. Last year, I had read that a layer of mulched leaves is good to place into raised beds, but when I did that, I found that much of it quickly blew away.

This year, I decided to plant crimson clover, a cover crop.

Cover crops, also known as green manures, are an excellent tool for vegetable gardeners, especially where manures and compost are unavailable. They lessen soil erosion during the winter, add organic material when turned under in the spring, improve soil quality, and add valuable nutrients.

HGIC page on cover crops

With a couple inexpensive packets of crimson clover, I sprinkled the seeds over the now empty raised beds, raked a bit to cover them lightly with soil, and then watered the soil most days. I could see sprouts in a week or so.

The clover will add a layer of protection over the winter, and then nitrogen and nutrients in April when I cut it down with a string trimmer and then turn over the soil.

Sounds easy enough. I’m all about lower-effort gardening!

Dan Adler
HGIC Web Support and Video Production

Plants not behaving as expected: vegetable garden edition

Two of the vegetable crops I grew this year are known for loving the heat: okra and eggplant. I grow eggplant in pots on my deck, to avoid flea beetle infestation, and okra directly in the ground in my community garden plot. Both of them produced adequately over the summer. Now it’s fall; we’re having days in the 70s and nights in the 50s, and there are fewer hours of sunlight in the day. Time to pull the summer crops, right?

Except – boom! Both the okra and the eggplant are going gangbusters. More flowers, more fruits than in the hot summer months, by far.

‘Bride’ eggplant on a cool autumn morning

So why aren’t these plants following the rulebook? Do they not know how to read? Or have the rules changed?

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Climate change impacts on pollinators and pollination

Do you agree that the weather has been getting a bit crazy? Summers are getting extreme, some being dry, others overly wet and too hot, the winters too warm, hurricanes and tornadoes becoming more common and stronger. Climate change is here, but what does it mean? Does it even matter? In this post I want to spend some time talking about why these strong changes in our climate do not just affect us, but mostly organisms that help us survive, like our beloved pollinators and the plants with which they interact.

What is climate change?

Climate change is any change in the mean and/or the variability of the climate, which persists for an extended period (decades or longer). This means that when we hear about climate change, people can be referring to any long-term change that has been detected in the records of temperature and precipitation, as well as the variations in their extremes and averages over time. Although we tend to think about the current climate change as increases in temperature, temperature is just one aspect of it. Often, it is also the precipitation patterns that are affected, leading to extreme rainfalls or droughts. Climate change is not just a climatic curiosity; because all the places and environments we live in and obtain our foods and livelihoods from are affected by climate, changes in climate affect our lives and those of other organisms with which we coexist.

How does climate change affect pollinators and pollination?

Like all organisms, plants and pollinators are only able to survive under specific climatic conditions. If the conditions change, their options are adapting to the new conditions, migrating to regions where their optimal conditions are still present, or going extinct.

Evolving and adapting to the new and fast-evolving climatic conditions has not been often observed in the case of pollination interactions. Most species are either observed to display what is called plasticity and use their already-evolved ability to adjust to different conditions. This allows them to tolerate more extreme conditions with possibly a small loss in their ability to obtain food, grow, or mate. In the USA, it was shown that some species of bees can advance their emergence time when the winters are warmer, and match to some extent the advancing in the flowering season associated with warmer winters or early springs.

Orange-legged Furrow Bee
The Orange-legged Furrow Bee (Halictus rubicundus) is a species that has been shown to be advancing its time of emergence with increasing temperatures. Photo: M.L. Legrand.

Most species, however, respond to these changes in the climatic conditions by dispersing to new regions, where their preferred conditions are still present. For example, species from Maryland, may disperse further north under a warming climate. Likewise, species that live on the slopes of mountains may disperse upwards, to higher altitudes. However, this is often impossible, when, for example, northern latitudes do not offer the right habitat (e.g., the preferred plants are not available or there is no more natural habitat left due to human pressure), when it is impossible to disperse further to the poles (e.g., for cold-adapted species), or when it is impossible to move higher on a mountain (e.g., for alpine species). These species see their ranges become smaller and smaller, until their population becomes too small to avoid extinction.

various species of butterflies
Some species, like the Giant Swallowtail and the White-M and Red-banded Hairstreaks, have been expanding their ranges northward (top row, left to right). Others, like the cold-adapted Atlantis Fritillary or the Arctic Skipper are likely to become at least locally extinct (bottom row, left to right). Photos: T. Eagle, S. McCann, G. Lasley, S. Elliott, S. King.

Finally, other species are unable to disperse at all, because they may not be mobile or because they move too slowly for the pace of climate change. Although only through modelling approaches, studies suggest that this may be the fate of many mid-Atlantic bumblebee species like the Perplexing or the Golden Northern bumblebees, which may become slowly doomed to extinction.

Perplexing and Golden Northern Bumblebees have been predicted to become unable to track their preferred climatic conditions under many climate change scenarios. Photos: P. Pieluszyński, Molanic.

Climate change and extreme weather events however, also can affect the survival of pollination interactions, and not only of individual species. For example, species that are specialized on their floral preferences or their pollinators may be unable to survive climate change. If the winter is warmer than usual, certain plants and insects may start emerging and developing earlier than usual. If these advances in their developments do not match between the plant and the pollinator, the partners will not co-exist, which can have drastic consequences such as loss of food, nesting sites, or lack of seed production for lack of cross-pollination. This is one of the reasons why the Baltimore Checkerspot, Maryland’s state insect, is at such high risk from warming winters and is currently endangered in the state.

Baltimore Checkerspot caterpillar and adult butterfly
If there are warm spells during the winter, the Baltimore Checkerspot’s larvae leave their “winter sleep” too early, when their plant food is still unavailable to them, and are at high risk of dying from starvation. Photos: WikiCommons, S. Snyder.

Another way these changes in climate can affect pollination is through changes in the functioning of the interacting species. For instance, it has been recently shown that extreme rainfalls and heat are able to affect the quality and composition of nectar and pollen, the odor compounds present in flowers, and the ability of insects to move and reach the flowers for reward collection. This means that even if species were to still co-occur, these extreme climate events can affect their ability to encounter each other, which again, leads to their survival being harmed!

This is complicated! Can I do anything to help?

It’s true! Understanding all biological interactions and protecting species IS complex, but that doesn’t mean that there’s nothing one can do to help! Some ways to support pollination include providing a lot of resources for both the plants and the pollinators to survive. For example, planting many different native species and providing nesting resources in our green spaces supports pollinators that may be migrating to new areas, or ones that may be just under a lot of climatic stress.

Also, it has been thoroughly demonstrated that increased concentrations of carbon in our atmosphere are leading to the climate change patterns we are observing. The good news (if we react quickly) is that we may still be able to do something to revert it, and this does not have to be anything that affects our ability to survive. Even relatively simple behavioral changes like turning off unused lights at home, bringing the thermostat even 4 degrees higher in the summer, or reducing meat consumption make a huge difference in our carbon footprints.

If you would like to start helping pollinators by reducing your carbon footprint, I strongly recommend visiting this website to receive “personalized” free recommendations to successfully reduce your carbon footprints through simple (and also more complex) and very feasible actions. And if you would like to learn more, I also strongly recommend the webinar series by University of Maryland Professor Dr. Sara Via.

By Anahí Espíndola, Assistant 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!