Tomato Talk: Wilts and Tips for a Big Harvest

Nothing causes that sinking feeling like walking into the garden and seeing one or more tomato plants wilting. Not just some lower leaves that are yellowing, curling, or drying up from leaf spot diseases. No, I’m talking about healthy green leaves and stems that start to go limp. Oftentimes, this spells the beginning of the end for the affected plant(s) so it’s important to figure out what’s causing the wilting symptom. Even if you lose one or more plants this year you’ll want to prevent a recurrence next year. UME’s Home & Garden Information Center seems to be getting more tomato wilt questions this year than usual.

Wilting may indicate that roots or stems are injured, soil moisture has been too high or too low, or that the vascular tissue directly below the epidermis (skin) of tomato stems is blocked up with fungal or bacterial pathogens. Plants with disease-caused wilt should be removed. Here are some possible causes for wilted tomato plants in Maryland.

Fusarium wilt– this disease is caused by a soil-dwelling fungus. Lower leaves turn yellow and leaves and stems begin to wilt, often on one side of the plant. Leaves may revive overnight. Cutting affected stems lengthwise with a razor blade (directly below the surface) will reveal brown discoloration or streaking. The disease rarely infects all of the tomato plants in a row or a bed.

This fungus can survive in the soil for years even if the tomato is not grown in that location. One solution is to grow resistant varieties- look for those that are resistant to at least two of the three known races of fusarium wilt. Example:

Nature’s Bites F1: Fusarium Wilt 1, Fusarium Wilt 2, Fusarium Crown & Root Rot, Leaf Mold, Root Knot Nematode, Tobacco Mosaic Virus

Another option is to grow tomato plants in containers filled with compost and soilless growing media. Don’t set the containers on the garden soil that had the fusarium wilt problem last year. 

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Heat-tolerant greens

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 Traunfeld

Callaloo 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 Traunfeld

Tri-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

The Difference Between C3 and C4 Plants– University of Illinois

The Heirloom Collard Project collects and increases collard seed and documents the history of many American South varieties 

Malabar spinach, Basella alba. University of Wisconsin

Lettuce All Year in a Changing Climate– Sustainable Market Farming- Pam Dawling

World Vegetables: Principles, Production, and Nutritive Values. V. Rubatzky, M. Yamaguchi. 1997

By Jon Traunfeld, Extension Specialist, University of Maryland Extension, Home & Garden Information Center.

Read more posts by Jon.

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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Comfy plant places and new garden spaces for vegetables

Every time we plant a seed or baby plant in our vegetable garden we are hoping for the best outcome- a healthy crop and big harvest. Gardening success comes from learning about the needs of our crops and doing all we can to meet those needs. Climate change is causing us to think a little more deeply and holistically about those plant needs and our gardening practices.

In addition to making sure that plants have enough space, water, and healthy soil, we can alter how and where we plant our crops (“comfy places”) to help them adapt to increasing summer temperatures. We can also consider ways to expand or shift our food garden spots (“new spaces”) to better manage growing conditions and produce more food.

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Peat-free potting mixes

Sphagnum peat moss is valuable in horticulture because its fibrous structure helps it retain a lot of water and air while draining excess water. This has made peat a primary ingredient of soilless growing media (potting mix) around the world. These stable, light-weight, and porous products have been filling the benches, flats, and containers of greenhouse and nursery operators and flower and vegetable growers for decades. You’d be hard-pressed to find a gardener who has not benefited from soilless potting mixes for starting and growing plants, inside and outside.

What’s the problem with peat?

Peat is an organic substance formed from mosses, reeds, and sedges that accumulates and decomposes very slowly in waterlogged soils (bogs). Peatlands hold 30% of the earth’s soil carbon and occur mostly in cold, temperate regions. “Peat moss” used in horticulture typically refers to mosses in the Sphagnum genus.

The problem with peat is three-fold: stripping off peat from peatlands disturbs complex ecosystems; excavation releases enormous amounts of CO2, a major greenhouse gas driving climate change; and demand for peat-based soilless media is growing.

For decades, there have been calls to conserve the U.K.’s dwindling peatlands. Timelines are in place for soon phasing out peat as a growing media for gardeners and commercial growers. Most sphagnum peat is from Canada and there are no indications that Canada, with its vast peat reserves, will follow suit. But public demand for peat-free alternatives will drive the industry to develop new products.

Reducing the use of peat in horticulture will mitigate climate change and increase reliance on local materials as peat substitutes.

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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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