If I look back at this summer in the vegetable garden objectively, I’d say it was an average success. My garden produced a fair number of tomatoes, peppers, squash and cucumbers. We ate well. But it felt like a really hard year, and I don’t think I’m alone in that experience. We had some nasty heat waves and dry spells, and the plants and produce seemed extra susceptible to damage. I had more cracking and insect damage on my tomatoes than usual, and the plants gave up early due to all the fungal disease. Squash collapsed from vine borers and cucumbers got all the blights. My peppers were the biggest disappointment, battling bacterial leaf spot both in my own beds and at the Derwood Demo Garden. I think some infected seed was to blame, since a few ‘Big Red’ plants were the first to show symptoms, but the disease spread quickly to all the rest.
I’m very invested in gardening, so I’m not going to give up even though I know the struggles are likely to continue; our climate issues aren’t going to get any better and the bugs and diseases are here to stay. I don’t think you should give up either! But I can see how a beginner might feel very daunted.
Here are a few ideas about making your garden less exhausting and more rewarding. I’m writing them down because I need to read them as much as anyone!
Having grown up in the plains of Argentina, surrounded by large rivers, swamps, hot summers and humidity, I can attest that I am pretty “heat tolerant.” While others complain of the heat, I just enjoy the “embrace” that a hot day gives me. The heat in the last few weeks, however, was even too hot for me! And while I was trying to cool down, I was also worrying about what I was seeing outside: the plants, the insects, the soil… all suffering like me. And because I happen to work on some of these topics, I also knew that it wasn’t just that some plants were drying out; this heat wave (and drought) is also affecting the whole network of interactions that happen around us. So, today let me tell you a bit about how these extreme heat waves affect one of those interactions – pollination – and how what we do in our green spaces can help reduce some of those effects to the benefit of all.
Pollination is affected by heat in more ways than we usually think
Extreme heat waves and droughts such as those we have been experiencing recently affect not only us but also the ecosystems that are exposed to the heat. One of the most evident effects we may see is how much plants suffer. Just look outside and you will see hanging leaves, tiny flowers (if any), and a lot of dry material. As with all organisms, plants also have optimal temperatures at which they can survive; if the temperatures and water availability change, important body functions will not be able to be performed, and even some central parts of their bodies will fail.
In plants, one of those functions is photosynthesis, the process by which plants can make sugar using the energy of the sun, carbon dioxide (CO2), and water. This process is the way the vast majority of plants make their food. If the process is disturbed, the plant will have less energy available to survive, grow, and reproduce. It turns out that extreme heat and water needs affect the ability of plants to photosynthesize. The consequence of this is that, suddenly, the plant has less energy available, needing to enter a sort of “survival mode.” Along with this, the heat affects several protection systems that the plant has, especially those that protect the DNA (the genetic material), as well as the functioning of the machinery that literally “builds” the different parts of the plant. This inefficient protection leads to the DNA being damaged and the plant being poorly “built”, making that part or the whole plant start malforming.
During the heat waves, these beebalm plants had a rough time, with almost no flowers produced and a lot of the plant material simply drying out. Photo: A. Espíndola
In relation to pollination, we know that these changes explain why, under heat and water stress, plants become smaller in size, have tiny or no flowers, lose a lot of leaves and biomass in general, and have parts that start to look “funky.” The changes in the energy availability make the composition of some secretions change as well, such as with nectar, which tends to be less rich in sugars and less abundant (especially when drought is experienced).
These black-eyed Susans were able to make flowers this year, but they are significantly smaller than usual! Photo: A. Espíndola
As said before, flowers tend to be small or absent, but even when they are present, the petals and reproductive organs are often misshapen, with the plant becoming unable to produce seeds and fruits. Finally, and super importantly for pollination, a major effect of this is that heat affects pollen quality, reducing the amount that is produced and often making the pollen inviable… meaning that even if the pollen was to land on a stigma, it would likely not germinate, and fertilization would not take place. This latter point is worrisome because it means that even plants that are not animal-pollinated (e.g., plants pollinated by wind or water) will be unable to produce seeds and fruits.
Pollinators suffer the heat, and that affects their survival and pollination
Pollinating insects are also affected by the heat, and some of these effects are related to the same facts we mentioned for plants. On the one hand, like plants, pollinators also have their own DNA and “body-building” machinery that is disturbed by heat. Some of the major consequences of this are that their development can be either interrupted (the larvae or pupae die off) or interfered with. If the development is interfered with, we see malformations in different organs, such as the wings, legs and mouth parts, and particularly in males, of reproductive organs and sperm. Further, extreme heat appears to affect bee neurological abilities, with their behaviors and memory affected, as well as changes in the way they visit and manipulate flowers, which in turn makes pollination more difficult.
Along with these issues, because of the changes in nectar quality and quantity associated with plant heat stress that we mentioned earlier, the pollinators’ nutrition is also negatively impacted, which further amplifies the developmental, behavioral, and neurological problems mentioned above. Although all insects experience these types of effects when they are exposed to excessive heat, some of them are a bit better at protecting themselves from it. For example, it seems that social bees suffer less from excessive heat than solitary bees, while bees that nest in the ground or in stems tolerate it better than those that nest in cavities.
Here’s what you can do to help mitigate the effects of heat and drought
Although we can’t instantaneously reduce the heat, we can assist plants and insects to better tolerate these conditions. A very effective strategy is diversifying our green spaces, which can lead to local reductions of heat, either through the shade created by the plants and/or the reduction of the excessive presence of bare soil. In particular, this same plant diversification can also increase the amount and quality of foods available to pollinators during these heat events: more diverse plants mean more different types of possible nectar sources available to pollinators, which in turn would increase their chances of survival and boost their health.
If possible, one can also water plants in our green spaces. By doing this, the water stress will be reduced and at least part of the symptoms displayed by plants will also be mitigated. If one were to do this, it is important to water with a slow flow and for a longer period of time, so the water can properly enter the soil. Along with this, using mulch or letting the fallen leaves cover the ground will also help retain some of the soil humidity, all while also providing shelter to insects.
And besides diversifying and supporting our green spaces, it is thoroughly accepted that the current extreme heat and drought events we are seeing are a consequence of climate change. Starting to reduce our and our communities’ emissions is another way to help plants and pollinators, pollination, and at the end of the day, the production of many of the foods we depend on. You can check out this awesome website by Dr. Sara Via and learn about what we can all do, and even sign up for super informative seminars that help you become familiar with and start acting on some of these topics.
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!
Persistent wildfire smoke is new for Maryland gardeners. Experts seem to agree that smoke and ash do not pose a health risk for garden produce. Smoke diffuses sunlight but will probably not significantly reduce the total amount of light for photosynthesis. We have not heard/seen any reports of gardeners picking up smoky flavors in harvested greens or other vegetables or fruits.
Wash all produce prior to eating it raw or cooking with it
Wear an N-95 quality mask when working outside on days when wildfire smoke worsens air quality
Hose off plants if a noticeable soot layer develops from prolonged, intense smoke
Wildfire smoke has been shown to boost the levels of ozone and other air pollutants which can injure plants. Watermelon, squash, pumpkin, beans, and potato are especially vulnerable to high ozone levels (above 75 ppb).
Drought and damaging storms
Wildfire smoke interfered with weather patterns and likely contributed to cooler and drier weather across much of the state.
Mid-May through June:
Lower average temperatures
75% of state in moderate drought on July 3rd
Slow start for warm-season crops
July:
High heat and humidity
Spotty rainfall
Insect and disease issues increasing
The Maryland Department of the Environment announced a Drought Watch on July 10, encouraging voluntary reduction in residential water use.
Farmers, gardeners, and scientists have known for some time that tomato (Solanum lycopersicum) is sensitive to heat stress at flowering and fruiting. Pollination and fruit formation can be disrupted when temperatures >90⁰ F. during the day and >70⁰ F. at night. Other fruit problems like yellow shoulders and white internal tissue are also caused in large part by heat stress, especially when determinate (self-topping) varieties are grown and pruned heavily.
If you feel that high temperatures are reducing tomato flowering and fruiting in your garden you can try moving crops to spots receiving late afternoon shade or you can cover plants with 30% shade cloth (a mesh material that blocks about 30% of sunlight). Another option is to try some of the many heat-tolerant tomato varieties. Heat tolerance is a major focus for tomato breeders around the world.
This year, some HGIC staff tried four determinate, hybrid varieties developed by Southern breeders (the first three are from the University of Florida) that I started from seed at home. They all have excellent disease resistance:
Florida 91 (F1) 72 days (transplant to harvest). 9 to 11 oz. red tomatoes
Photo credit: Jon Traunfeld
Heatmaster (F1) 75 days (transplant to harvest). 7 to 8 oz. red tomatoes
Photo credit: Jon Traunfeld
Jamestown (F1) 80 days (transplant to harvest). 9 to 10 oz. fruit. Purported to have a deep red crimson gene and high lycopene content
Photo credit: Jon Traunfeld
Phoenix (F1) 72 days (transplant to harvest). 8 oz. red tomatoes
Tender spring lettuce and spinach leaves are just a memory for many Maryland gardeners. As we move into the summer season the types and flavors of garden greens expands significantly. While some, like Swiss chard and kale, can be cut or torn and dropped into fresh salads and dishes, most will benefit from some level of cooking, like sautéing on their own or being added to stovetop or baked dishes. Most of the summer greens below grow quickly and have a long harvest period. They help us improve food security and adapt to climate change.
General growing tips for summer greens:
Water, water, water and fertilize to promote rapid, healthy growth and maintain leaf and stem succulence
No row cover! They can cause a heat build-up. Instead, use insect netting to exclude insect pests
Plant summer greens in containers and move them to shady spots close to your front or back door
Create some shade for lettuces and other marginal crops like cilantro … plant on the north side of taller crops or try 30% to 50% shade cloth material
Most leafy greens below can be treated as cut-and-come-again crops: they put on new growth below each harvesting cut. Older, stressed foliage is less palatable
Explore seed racks and online seed catalogs for heat-tolerant crops and varieties
Leafy amaranth
Two well-adapted species for Maryland gardens are Amaranthus viridis (callaloo, also known as slender amaranth) and Amaranthus tricolor (Chinese spinach; leaves somewhat smaller than A. viridis).
Several species are very popular in Central and South America, India, Southeast Asia, and Africa. Nutritionally, they compare favorably with spinach and Swiss chard. Plants in this family use a special C4 photosynthetic pathway, also present in corn and sugarcane, which allows for vigorous growth under hot, dry growing conditions.
Leafy amaranth is basically a tasty and productive pigweed. Flowering accelerates with shorter days after the summer solstice. Frequent harvesting delays flowering and promotes branching. Immediately remove any flower stalks that emerge to prevent re-seeding.
Callaloo growing in 3-gallon bags in a high tunnel. UME Small Farms Program. Photo credit: Jon TraunfeldCallaloo can quickly become a weed problem. Don’t let plants flower. Each plant can produce >100,000 tiny seeds dispersed by water, wind, tools, and animals. Photo credit: Jon TraunfeldTri-color amaranth. Photo credit: Jon Traunfeld
Other heat-tolerant greens in the Amaranthus family:
Swiss chard and Perpetual Spinach (a.k.a. leaf beet) fall within the beet species- Beta vulgaris- and will produce large amounts of leafy goodness from spring through early fall. Orach (Atriplex hortensis) is another family member that grows best in spring and fall but can tolerate summer heat.
Two varieties of Swiss chard in the UMD Community Learning Garden. Photo credit: Jon Traunfeld
Leafy Brassicas
Several crops in the Brassicaceae plant family tolerate Maryland summers. Collard plants produce reliable and abundant harvests from summer through fall. ‘Morris Heading’ is an heirloom “cabbage-collard” variety found in Baltimore City community gardens throughout the growing season. ‘Green Glaze’ is touted as being heat-tolerant but I am not aware of studies that looked at temperature effects on the productivity of collard varieties.
Collard plant in late July surrounded by common purslane, and edible weed. Photo credit: Jon Traunfeld
Mustard and kale are somewhat less heat-tolerant than collards. ‘Green Wave’ and ‘Red Giant’ mustards and ‘Lacinato’ kale are common varieties grown in summer gardens in Maryland. I’m very curious about Portuguese kale (Couve tronchuda). It resembles collard and is described as sweet and tender and more heat-tolerant than other kales. If you grow it please leave a comment about your experience.
‘Lacinato’ kale (a.k.a Tuscan kale, dinosaur kale, black kale) growing in Baltimore City in late July. Leaves are harvested from the bottom. Photo credit: Jon Traunfeld
Check seed catalogs for mild-flavored leafy Asian greens that hold up well in warm weather like Tokyo Bekana (Brassica rapa var. Chinensis), ‘Komatsuna’ (Brassica rapa var. perviridis), Vitamin Green and Tatsoi (Brassica rapa Napa group), and ‘Chijimisai’ (tatsoi x komatsuna).
Malabar spinach
Basella alba (green stem) and Basella rubra (red stem) below are “summer spinaches” that produces a vigorous leafy vine. Leaves and stems can be sautéed or used to thicken soups and stews.
New Zealand spinach
New Zealand spinach (Tetragonia tetragonoides) below is a low growing annual with a spreading habit that has somewhat fuzzy, arrow shaped leaves, and mild spinach flavor.
Photo credits: Jon Traunfeld
Molokhia (Corchorus olitorius), known as Egyptian spinach and jute leaf, is an important food plant in the Middle East, Africa, and Asia. It’s higher in vitamins and minerals than most other leafy greens. This is the jute plant, known for its strong stem fibers. Young leaves can be eaten fresh, sautéed, or used to thicken soups and stews.
Sweet potato (Ipomoea batatas) – shoot tips, young leaves, and tender stems are excellent in many top-of-the-stove dishes. Harvesting young foliage, even on a regular basis, will not reduce your harvest of sweet potato roots later in the season.
Sweet potato plants with a less typical cut-leaf shape. Photo credit: Jon Traunfeld
Hibiscus as a Leafy Green?
Sunset hibiscus (Abelmoschus manihot) and roselle hibiscus (Hibiscus sabdariffa) leaves have a compelling lemon-sour flavor similar to garden sorrel. These plants are in the Malvaceae family along with cotton and okra, planted throughout the tropics and sub-tropics. Roselle is also grown for its strong fibers and its fleshy calyx which farmers and gardeners use to make tea, juice, and preserves.
Green stem hibiscus plant harvested for its leaves used in many Indian foods. Photo credit: Jon Traunfeld
Don’t Dismiss the Lettuces!
Lettuces are generally a cool-season crop but these varieties have demonstrated some level of heat tolerance:
‘Merlot,’ ‘Speckled Bibb,’ ‘Adriana,’ ‘Jericho,’, ‘Coastal Star,’ ‘New Red Fire,’ ‘Starfighter,’ ‘Tropicana,’ ‘Red Cross,’ ‘Magenta,’ ‘Cherokee,’ ‘Green Star,’ ‘Summer Crisp,’ ‘Little Gem,’ ‘Muir,’ ‘Burgundy,’ ‘Bronze Beauty,’ ‘Forlina,’ and most oakleaf types of leaf lettuce. Asian sword leaf lettuces, (pointed lettuce) have long, thin leaves and are described as crisp and tender with a mild bitterness.
One of the sword lettuces growing mid-summer in a Howard Co. community garden. Photo credit: Jon Traunfeld
An Auburn University study found that ‘Aerostar’, ‘Monte Carlo’, ‘Nevada’, ‘Parris Island’, ‘Rex’, ‘Salvius’, and ‘Sparx’ grown in a “hot greenhouse” out-performed 10 other heat-tolerant lettuce cultivars and received the highest flavor and texture ratings.
Give some of these greens a try this summer. The investment in seed, space, and time is minimal and you may discover some surprising new textures and flavors.
Resources:
Callaloo recipes– Dr.Nadine Burton, Alternative Crops Specialist, UMES Extension
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.
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.
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.
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.
Benefits
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.
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
