Most North American gardeners continue to harvest vegetables in the middle of summer. But in tropical and subtropical regions, most of the traditional veggies have finished producing and have long ago expired from the heat and humidity. True, there’s a lot to be said for planting heat-tolerant okra, hot peppers and southern peas, but there are other options for veggie gardens in the hot zones: Plant cover crops and/or let the sun bake pests away through soil solarization.
Pigeon pea (Cajanus cajun) can be planted as a living mulch and is a great choice to use as a cover crop in hot weather.
Photo Credit: Carol Cloud Bailey
Whether you’re solarizing a large planting area or a small one, the plastic used to solarize soil should be clear and spread smoothly and tightly, with few wrinkles.
Photo Credit: Sunshine State Carnations, Inc., Hobe Sound, FL
Beautiful in the landscape, pearl millet is a valuable grain cover crop for home gardeners. It’s heat- and drought-tolerant; birds love the seed; and the grain is versatile in the kitchen, where it can be steamed or roasted like rice.
Photo Credit: James H. Schutte
Known as Southern peas, cowpeas or blackeyed peas, Vigna unguiculata is a heat-loving legume that can be grown during the hottest summers for its tasty peas, nitrogen-fixing ability and green manure value.
Photo Credit: Gerald L. Klingaman
Soil thrown over the edge will anchor the plastic in place and seal in the planting bed to work like a pressure cooker.
Photo Credit: Sunshine State Carnations, Inc., Hobe Sound, FL
Cover Crops. Cover crops are plants grown for the specific purpose of tilling them back into the soil for amendment. As these plants decompose, they add organic matter (OM) to the soil. OM helps soils hold on to water and nutrients. It’s often lacking in sandy, poor soils.
As a cultural garden practice, the planting of cover crops has been a standard for centuries. Besides increasing soil OM and thereby water-holding and nutrient capacity, cover crops can prevent soil erosion, reduce weed populations in future crops (by out-competing them during the off-season), provide habitat for wildlife, increase air space, improve soil structure and reduce soil-dwelling nematodes and other pests. If a legume is planted as a cover crop, nitrogen is fixed in the soil, reducing the need for fertilizer. Also known as a green manure, cover crops should be fast-growing, adapted to the growing season and climatic conditions and produce lots of lush top growth.
Since the main growing seasons in tropical and subtropical locals are fall, winter and early spring, cover crops are planted in the heat of summer. Like all things, each type of plant used for a cover crop has advantages and disadvantages and provides different benefits. Some of the plants good for planting as a green manure include legumes and grains.
Legumes good for summer cover in tropical and subtropical locations include Alyce clover (or white moneywort; Alysicarpus vaginalis), cowpeas (Vigna unguiculata), hairy indigo (Indigofera hirsuta), sunn hemp (Crotalaria juncea), pigeon peas (Cajanus cajun) and velvetbeans (Mucuna pruriens). Grain cover crops include pearl millet (Pennisteum glaucum) and Sorghum. French marigolds (Tagetes patula) are also a good choice for home gardens; they offer the advantage of adding OM to the soil as a cover crop, may confuse and/or repel pests naturally with their smell and have been proved by reliable research to reduce populations of some harmful nematodes when planted thickly.
Seeds for cover crop plants are not often found at local nursery or big box stores; check with local feed and seed stores, agricultural suppliers and online retailers for cover crop seeds. When planting annual cover crops (as those suggested here), the seed may be broadcast or planted in rows. Allow your crop to grow into full, lush plants, then turn those living plants under while they’re still growing. It’s acceptable to harvest a “mess” of cowpeas for the table before reaping the advantages of the plants as green manure.
Soil Solarization. Another common practice in the subtropical and tropical edible garden is soil solarization. Wherever plants grow, there will be pests. Common vegetable garden pests include weeds, fungi, insects, viruses and (the most difficult to control) nematodes. Whether trying to maintain an organic garden or not, one of the best ways to clean up the soil is solarization.
Soil solarization uses radiant heat from the sun, collected through clear plastic, to heat the soil to a temperature that kills pests. It’s been proved that soil temperatures may rise in excess of 130 degrees F down to 6 inches deep in a properly prepared bed. In temperate climates, the use of this tactic may mean taking the garden or portion of the garden out of production for a summer. In tropical or subtropical areas, this process can – and should – be employed every year or two.
Solarization is a simple process, one that requires sun and heat – two things gardens in hot climates have in abundance – and time. The best season for this process is during high and late summer, when the sun is at its highest angle and is most intense.
Preparation is important for success. The soil must be well-tilled to destroy clods and plant debris so heat conduction will be uniform through the soil. (If using a cover crop, allow several weeks between turning the crop under and solarizing to allow the crop to decompose.) Before covering the garden, you should basically prepare the soil as you would for planting: Be sure the soil is uniform without air pockets because such pockets could prevent heating of the soil in localized areas. The soil should be moist, too, either by self-irrigation or wait to cover after a good rain. Soil moisture should be high, as wet soil conducts heat better than dry.
Use clear polyethylene plastic to cover your planting beds, not black. Clear plastic allows soil temperatures to rise faster and higher because sunlight passes through clear plastic to heat the soil directly – the greenhouse effect at work for good! Thin plastic (l-2 mil) rather than thick (6 mil) has been reported to favor deeper, faster heating, although both eventually allow the soil to heat, and thicker plastic is less likely to tear. After stretching out the plastic so that it’s smooth, cover the edges with soil, sealing in the garden. This final step helps keep in that heat and moisture.
The soil should remain covered for at least 4-6 weeks. Leave the plastic in place until a week or two before planting time, then remove it and allow the soil to cool. Don’t till or disturb solarized soil before planting in it, as this would bring untreated soil to the surface. Avoid bringing contaminated plants or untreated soil into the treated bed; use sterile soil for starting seeds.
Clean garden soil that’s rich with organic matter and nutrients is a gardener’s dream! Lucky for us, such valuable soil is easy to achieve thanks to the use of simple cover crops and soil solarization!