Maryland Grows

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.

Warmer, wetter, wilder

Severe or unexpected weather has always been the biggest “beyond our control” challenge for farmers and gardeners around the world. Recent scientific reports show that climate change effects are “widespread, rapid, and intensifying” (IPCC- 6th Assessment Report). In the mid-Atlantic, the number of frost-free days is increasing, winters are warmer, “intense precipitation events” (>2 in. /24 hrs.) are becoming more frequent (warmer air holds more moisture), and coastal farmers are battling saltwater intrusion of cropland.

Here are highlights from the Capitol Weather Gang’s 2021 summary of Washington, D.C. weather:

  • 7 days of wind gusts >50 mph during March-May; some damaging >60 mph wind gusts
  • Numerous tornadoes from severe storms and Hurricane Ida
  • Coastal flooding partly from slow moving storms
  • 5th warmest year on record; Oct. and Dec. were each the 2nd warmest months on record
  • 48 days >90 ⁰F., 8 more days than the 1991-2020 average
  • 8 record-high minimum day temps which reflects the fact that nights are warming faster than days

It’s remarkable that the small, steady increases in average temperatures caused by humans over the past 200 years can produce such profound changes! 

Resilient crops and cultivars

Heatwaves, drought, hail, strong winds, and heavy downpours can all stress plants. Crops such as snap and lima bean, squash, pepper, and tomato are especially sensitive to heat stress at flowering and fruiting. Climate change resiliency in specific vegetable crops and cultivars often refers to heat tolerance, but can also be the ability to grow in low-moisture soil, or mature quickly before prolonged hot weather sets in. Selecting heat-tolerant crops and cultivars is one strategy for addressing warming temperatures. Other approaches include moving crops to shadier garden spots, planting earlier or later, and covering plants with shade cloth materials. Pay close attention to seed catalog descriptions. Some companies have a “heat-tolerant” page or section.

Heat-tolerant warm-season crops to try

Southern peas (cowpeas) and yardlong (asparagus) beans come in a variety of fruit and seed colors and patterns. They tolerate hot, dry weather and fix nitrogen from the air, providing your soil with “free” nitrogen after plants decompose. Look for cultivars that can be trellised to save space.

blackeye pea plants
Blackeye pea plants

Okra makes beautiful flowers and an abundance of fruit pods through frost. All parts are edible.

Sweet potato is a durable storage crop plus you can harvest and eat young leaves and shoot tips during the entire growing season. Save space by growing plants vertically. (Also, see the video: How to Start and Multiply Sweet Potato Plants.)

Sweet potato plants growing on a metal support structure in the
Master Gardener Learning Garden at the Maryland State Fair.

Heat-tolerant tomato cultivars

Hybrids: Summer Set, Sun Leaper, Solar Set, Sun Sugar, Red Bounty, Phoenix, Heatmaster, Solar Fire, Sanibel, Florida 91

Open-pollinated: Creole, Homestead, Roma, Arkansas Traveler, Porter

Some commercial tomato growers in the mid-Atlantic are observing reduced fruiting and fruits with yellow shoulders and white internal tissue caused in large part by heat stress. For home gardeners, this is probably more likely to occur in heavily pruned determinate cultivars grown in full sun, especially in urban/suburban locations with a pronounced heat-island effect. There is much research and breeding work underway to develop cultivars that can tolerate heat stress.

Quick-maturing tomato cultivars

Is your goal is to start harvesting long before sweltering summer weather? There are many fast-maturing (55-65 days from transplanting) cultivars that will typically produce a lot of fruit by late July. Early Girl, 4th of July, Moskvich, and cultivars with “Oregon” in their name are a few examples. Cherry and pear tomatoes are often fast maturing. Juliet is a 65-day, grape-shaped hybrid tomato that produces big crops of perfect fruits.

Heat-tolerant lettuces

Most lettuces will bolt when temperatures are >85 ⁰F. Crisphead (iceberg), oakleaf type lettuces, Merlot, Bronze Arrow, Bronze Beauty, and Jericho are more heat-tolerant. Dutch breeders developed the Salanova series that includes some heat-tolerant cultivars, such as Muir, Nevada, and Cherokee. Johnny’s Selected Seeds is the sole U.S. distributor.

Heat-tolerant broccoli

Cold weather can force spring-planted broccoli to bolt and high heat damages broccoli buds. The Eastern Broccoli Project is a decades-long effort to increase commercial broccoli production in the Eastern U.S. A number of heat-tolerant cultivars have been developed. University of Delaware researchers found good heat tolerance in Eastern Crown, Millennium, and Green Magic.

Heat-tolerant greens

Check seed catalogs for mild-flavored leafy Asian mustards like Vitamin Green that hold up well in warm weather. Callaloo (Amaranthus viridis) leaves and succulent stems grow abundantly throughout the summer and early fall and can be prepared and used like spinach.

Callaloo growing at the UMES Education and Demonstration Farm in Princess Anne.

Heat-tolerant beans

High temperatures are interfering with the pollination/fertilization of lima bean and snap bean flowers and reducing yields. University of Delaware researchers are finding that high night temperatures are more responsible than day-time warming for this problem. See research results in the references below.

Speaking of seeds…

January 29th is National Seed Swap Day! Some area seed swaps have already happened. There is one upcoming event, the seed swap hosted by Kathy Jentz and Washington Gardener Magazine, at Brookside Gardens on February 22. Find details and registration information here: http://seedswapday.blogspot.com/.

Past blog articles about vegetable seeds

Seeds and Seed Catalog Jargon
Are Cheaper Vegetable and Flower Seeds Just As Good As More Expensive Seeds?
Starting Vegetable Seeds Under Fluorescent Lights
Seeds to Die For

References

Climate Change in Maryland (UME)
D.C.’s second-warmest December on record caps fifth-warmest year
Mid-Atlantic Regional Climate Impacts Summary and Outlook: Fall 2021
NOAA State Climate Summaries
UDEL- Heat Stress Trial With Tomato
UDEL- Heat Tolerant Vegetable Varieties
Genetic and Molecular Mechanisms Conferring Heat Stress Tolerance in Tomato Plants

By Jon Traunfeld, Extension Specialist, University of Maryland Extension, Home & Garden Information Center. Read more posts by Jon.

Variety is the spice of life: creating a new garden with native plants

Nothing like starting out a blog with a cliché, right? But this perfectly sums up one reason to change from a monotypic lawn to a mix of native plants. Instead of looking out at a sea of sameness, the diversity of colors, sizes, and shapes of plants offer a more pleasing landscape to view. And, bonus points, more and different kinds of plants attract more and different kinds of butterflies, birds, and beneficial wildlife!

butterfly milkweed with monarch caterpillar
Butterflyweed planted in spring 2020 provides food for Monarch caterpillars later in the summertime.

A do-it-yourself garden is harder but more fulfilling

Once you figure out that you do want more variety of plants instead of lawn in your yard, the real planning begins. But, it can be hard to know where to start – do you just chop up the lawn and start planting? How much will it cost? What’s the maintenance on these plants? What about soil conditions? Don’t worry! There are some really good online tips for beginners. To sum mine up: start small, don’t overthink it, and stick to things you like looking at.

For example, my sister moved into a small house with a fenced backyard. She knew she wanted to avoid the pain of mowing. She knew she wanted low-maintenance, flowering plants. And since she’s a redhead, she knew what colors she liked (hint: little to no red flowers). The first thing we did was start tracking the sun, in both the front and back yards. Each month over the winter, we took a picture in the morning, at noon, and in the evening. We also got started on the paths needed through the garden areas.

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Houseplants – The Garden Thyme Podcast

two houseplants on a windowsill

Happy New Year! It is hard to believe that we are already in a new year. We are kicking off our third season by sitting down with Extension Educator Ginny Rosenkranz. Like many of you, during the pandemic our acquisition of houseplants increased exponentially. Ginny guides us on caring for all of our botanical beauties.

We also have our: 

  • Native Plant of the Month, Musclewood, Ironwood (Carpinus caroliniana) at ~24:55
  • Bug of the Month, Ice crawlers or ice bug family Grylloblattidea at ~29:05
  • Garden Tips of the Month at ~31:50

To listen to the podcast visit https://www.buzzsprout.com/687509.

podcast sound wave image

We hope you enjoy this month’s episode and tune in next month for more garden tips.

  1. If you have any garden related questions please email us at UMEGardenPodcast@gmail.com
    or look us up on Facebook at https://www.facebook.com/GardenThymePodcast.
  2. For more information about University of Maryland Extension and these topics, please check out the UME Home and Garden Information Center website at https://extension.umd.edu/hgic.

The Garden Thyme Podcast is a monthly podcast brought to you by the University of Maryland Extension. Hosts are Mikaela Boley- Senior Agent Associate (Talbot County) for Horticulture, Rachel Rhodes- Agent Associate for Horticulture (Queen Anne’s County), and Emily Zobel- Senior Agent Associate for Agriculture (Dorchester County). Theme Song:  By Jason Inc.

Planning your garden to support specialized pollinators

Looking out my window, as the ground is covered with snow and I am getting ready for another snowstorm coming tonight, it seems ironic that I have been spending many hours these days ordering seeds and planning my garden. While I am thankful that the winter brings some rest to the soil in my garden, planning this season brings me happy memories of the scents and buzzes in my yard during the growing days… which reminds me that I should also plan for my little buzzing pollinator friends when I plan what to grow this season. In today’s blog, I want to chat about how we can plan for many types of pollinators, with a special focus on planning for specialists and not just for generalist pollinators.

Specialist pollinators – never heard of them?

As we mentioned in a previous post, pollinators visit plants to feed on nectar and/or to collect pollen to feed themselves or their offspring. However, pollen is not just there for pollinators to feed on; pollen is central to plant reproduction, so plants tend to make it both attractive to pollinators but hard to digest. For this reason, and in order to be able to properly digest the pollen, pollinators are often specialized in their pollen choices. This is because being able to digest the compounds that plants add to their pollen to make them hard to eat requires some level of adaptation, which often involves a trade-off with the ability to eat anything. There are, of course, many levels of specialization, and, while many pollinators feed on many plant families, others are more specialized than that, and feed on only specific plant genera or even species! For us gardeners, this means that if we want to support many different pollinators, we need to make sure that we are also providing for those very specialized pollinators as well!

Luckily for us, the floral choices and pollen specialization is known to some extent for Maryland and Eastern USA bees (see this site to learn more). For this reason, we know that many specialized bees in our region are also rare or uncommon… another reason to try to provide resources for them!

Who are pollen specialists in our region?

Many known pollen specialist bees in our region belong to bee genera Andrena, Colletes, Osmia, and Melissodes, which have many species considered rare or uncommon in Maryland and Mid-Atlantic.

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Don’t grow these edible plants! (unless you really want to)

It’s seed catalog season! If you’re anything like me, you’re paging through them right now marking possible purchases for the 2022 growing season. (Happy New Year, by the way.) On my first pass, I always mark much more than I can plant in my own gardening space, and now that I’m no longer choosing what to grow in the Derwood Demo Garden, my selections are further limited. I have to make sensible choices, darn it. Nothing too big or aggressive, or that takes too long to produce, or is marginal in our climate, or that I’m not sure I like to eat. Good thing I’ve had all that practice trying and failing.

Now, I would never limit anyone else’s choices, or tell them they won’t succeed at what they’re attempting. I’m usually all for stretching the boundaries. So the spirit of the list below is not to discourage; it’s just to pass on what hasn’t worked for me. Maybe some of these plants have done great for you, or you’re convinced you can get past the challenges. But if your space and time is limited and you have to be realistic, feel free to make use of my what-not-to-grow advice.

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Why light levels are important for indoor plant growth

plants growing under artificial light indoors
Photo: Miri Talabac

Typically, insufficient lighting is the limiting factor for indoor plant growth and flowering, plus the reason for spindly seedlings. Most light fixtures in our homes and offices – especially those still using incandescent bulbs or those with energy-saving bulbs that mimic incandescents – don’t give off enough energy for plants to survive or thrive on long-term. In addition, windows block a surprising amount of sunlight intensity compared with the same spot just outside the glass. Insect screening outside a window reduces intensity even more.

Artificial lighting can either supplement natural light or be the sole light source for plants. Plants tolerate levels of light outside of their preferred range, but sensitivities vary from species to species. Over time, the consequences of inappropriate light levels may impact a plant’s health and alter its appearance, even if it isn’t immediately noticeable.

The importance of light to plants

For plants, light is food. We think of fertilizer as plant “food,” but in reality, it is more akin to a multivitamin than it is a meal – it supports how they use their food (carbohydrates from photosynthesis) and helps build tissues, pigments, hormones, defensive chemicals, and so forth – but it’s not providing the calories they need to survive and grow. They certainly can “fast,” so to speak, such as spending a few days in a box in transit or remaining semi-dormant in winter, but prolonged light deprivation from insufficient lighting will have negative impacts on plant health akin to slow starvation.

Plants may lack eyes, but they can still “see” light by detecting its colors, intensity, and duration. Coupled with temperature or precipitation, it can tell them what season it is for the purposes of growth and reproduction (flowering). Weather can fluctuate from year to year, but the patterns of daylength and general light intensity remain the same and are the most reliable environmental cues for the plant.

Plant reactions to light

As plants grow, their leaves develop in response to the environmental conditions they are experiencing at that time. This allows them to photosynthesize as efficiently as possible. However, this means they have limited ability to change their leaf physiology after the leaf has matured in order to deal with markedly different levels of light. This is one reason plants adjusting to a change in conditions (such as going from a greenhouse or patio to inside your home) may drop leaves or need to replace leaves in order to acclimate.

indoor plants growing under artificial light
Photo: Miri Talabac

How plants deal with too much or too little light

Plants cannot move very far when seeking more or less light. Instead, they adjust their physiology to try to adapt. While fully-developed and expanded leaves don’t change size, a plant can change a leaf’s position by tilting it to intercept more light or to avoid bright light. Plants can also change stem length as they grow, reaching or leaning towards light if they’re getting too little, or staying squat and somewhat stunted if getting too much.

The points on the stem where leaves attach are called nodes. The sections of stem between the nodes are called internodes. In bright light, internodes tend to be short so the leaves are held closer together, where they can shade each other. In dimmer light, internodes tend to be long, so each leaf collects more light and self-shading is minimized. Etiolation is the term for longer-than-usual internodes, when a plant is “stretched” or “leggy” and trying to get more light.

Other changes can occur as a plant reacts to increases or decreases in light while it’s growing.

  • In light that’s too bright:
    • new leaves mature smaller than average because they don’t need as much space to collect enough light
    • foliage that is normally deep green can “bleach” or “sunburn/scorch” as intense light damages tissues, or it can blush reddish as a means of protecting itself with pigments that act like sunscreen (sometimes referred to as “sun-stressed”)
  • In light that’s too dim:
    • new leaves mature larger than average because they need more space to collect enough light
    • foliage with rich colors – burgundy, red, yellow – become greener when light isn’t intense enough because the plant needs to use more chlorophyll
    • variegated plants may lose some of their multi-colored patterns in insufficient light
    • growth slows or becomes sparser overall and plants may refuse to bloom
intense light changes leaf color from green to reddish
Photo: Miri Talabac

What are your plants telling you?

If you’re already growing plants indoors, you may have noticed changes in their appearance, either since you brought them home or over the course of a year. Some of these changes may be due to differences in lighting, though other factors can play a role as well and complicate your evaluation. (Soil moisture, nutrition, humidity, temperature, and plant stage of maturity can all influence leaf appearance and plant growth.) If you think a particular plant has been declining or failing to thrive, see if key features – leaf color and size, stem length – suggest light levels are the reason.

Coming up: we’ll dive into some jargon! In our next installment, we’ll introduce indoor lighting options and some technical terms that are important to understanding what product specifications mean. Don’t be intimidated or skip over this – it’s very useful in helping you decide how suitable a light will be to give you the best performance.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Read the previous article in this series, An introduction to gardening under lights, and additional posts by Miri.

Q&A: Winter gardening tasks

Q: Is there any outdoor garden task this time of year that I may be forgetting to do? I’ve foregone a fall clean-up for the benefit of overwintering wildlife, and the lawn and veggie garden are “asleep” for the season.

A: There are a few things that are good to accomplish during the dormant season. Yard tools like pruners, loppers, shovels, spades, and mower blades are best stored clean, sharpened, and oiled. There may be local businesses that offer sharpening services, but you can also do it yourself with a metal file or sharpening stone or rod.

Ideally, sharpen mower blades annually so the turf doesn’t have the added stress of ragged, torn leaf blades which can be more vulnerable to infection. A steel wool scrubber or a wad of sandpaper can take off early stages of rust and caked-on sap before you focus on the blades of pruning tools and shovels. Good-quality hand pruners can usually be disassembled for easier maintenance, and lightly wiping with oil afterwards helps lubricate the metal and resist rust. Linseed oil (or vegetable oil in a pinch) can be rubbed into wooden tool handles to protect them from aging.

Check on the location of pesticide containers and protect them from extreme temperatures (including freezing). Always store them away from human and animal food and well-secured from children and pets. Products you rarely use should be dated (if you recall when you bought or opened them) since they may only have a useful shelf life of a couple of years. Old pesticides can be disposed of by looking for household hazardous waste collection sites near you.

If you have staked any new plantings, check their ties to make sure the plants still have wiggle-room and bark isn’t being abraded. Stakes that have been in place for six to twelve months can be removed; they’ve either done their job by now or weren’t working in the first place. (Staking is actually not often needed, but at the very least it’s key to let a staked plant’s trunk sway in the breeze so stabilizing root growth and trunk thickening are stimulated.)

Similarly, if you left ID tags tied to any plants, remove them and any other plastic or elastic nursery tags before they damage the stems. Otherwise, any material that gets embedded in expanding growth will be impossible to remove and could cause branch decline in the future if it interferes with sap flow. Alternatively, tags may disintegrate over time and fall off, which means you’ll have lost your plant name. Tags will be easier to spot now on deciduous plants. Keep a record of the plant ID another way – a garden diagram or journal, or written on a stake at the plant’s base – as variety-specific features might impact care advice or future troubleshooting.

Lastly, if you’re overwintering hardy plants in containers, consider using “pot feet” or “pot risers” to raise the pot’s base off decking or pavement by an inch or two. This lets excess moisture clear the drainage holes so it doesn’t freeze into an ice dam, which would risk flooding roots. Any sturdy material where you can find several pieces the same height would suffice, but you could also purchase them in an array of materials, often in packs of three or four “feet” per pot.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read additional articles by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension.