Editor’s Note: This is a reprint of an article by Jon Traunfeld, Extension Specialist, University of Maryland Extension, Home & Garden Information Center. As you peruse seed catalogs this winter, Mr. Traunfeld’s guidance will enable you to choose the most heat-resilient varieties.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. 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, black-eyed peas) and their relative, Yard-long beans (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.
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.)
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. The Batavia lettuces include some heat-tolerant varieties, including Muir, Nevada, Cherokee, Sierra, Pablo, Concept, Cardinale, and Loma.
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.
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.
References
Featured Photo: Hibiscus sabdariffa (roselle). Photo: Jon Traunfeld
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 SummariesUDEL- Heat Stress Trial With Tomato
UDEL- Heat Tolerant Vegetable Varieties
Genetic and Molecular Mechanisms Conferring Heat Stress Tolerance in Tomato Plants
University of Arkansas Cooperative Ext/www.uaex.uada.edu/southern-pea.aspx
University of Maryland Extension/Growing Beans in a Home Garden
University of Maryland Extension/Leafy Greens for the Summer Garden
University of Maryland Extension/Heat-tolerant greens
This is useful information, as being prepared is the best way to adapt when situations change.
I think you might have lost a line in the heat-tolerant lettuce section. Salonova is Johnnie’s range of multi-leaf lettuces, which I don’t think are particularly heat tolerant. Muir, Nevada and Cherokee are some of the Batavian heat-tolerant varieties. Others include Sierra, Pablo, Concept, Cardinale, and Loma. Many seed companies (especially in the South) sell some of these varieties. I grow lettuces all summer, using mostly Batavians.
Good catch, Pam Dawling. We have now fixed the error, and we’ve also added your list of other heat-tolerant Batavians. Thanks!