Soybeans for Summer
By Glenn I. Teves, County Extension Agent, UH CTAHR
In a month, summer will be upon us and with it, longer and hotter days. Although most vegetables don’t enjoy this kind of weather, a few will respond favorably to heat and stress, which can enhance their nutrient content. According to research by U.S. Department of Agriculture, the Vitamin E or alpha-tocopherols content of early maturing varieties of soybeans can increase three-fold when under water and heat stress. Vitamin E is an important antioxidant, and most Americans are deficient. Soybeans are one of the most important food crops due to their protein content, in addition to other health benefits, including phytonutrients like phytosterols that lower the “bad” cholesterol that can lead to heart disease and stroke.
The raw material for many high vegetable-based protein products such as tofu and soymilk, the vegetable soybean, is known as edamame to distinguish it from the grain or industrial soybeans, most of which are genetically modified. Edamame means “beans on branches.” Grown in Southeast Asia for over 2000 years as an important protein source, many of us were raised on it just boiled with salt water and ready to eat, similar to boiled peanuts.
Edamame thrives in slightly acid soil of pH 5.5 to 6.5. Most edamame varieties are long-day plants and will only produce good yields when planted between March and August, including Beer Friend, Early Hakucho, Midori Giant, Mojo Green, Sunrise, Butterbeans, and Korean Black. Edible soybean varieties developed by University of Hawaii can be grown during winter months, including Kailua and Kahala soybeans, and are also resistant to root-knot nematodes.
Soybeans are planted directly into the garden at a depth of 1 to 1 ½ inches deep, 18 inches between rows, and 3 to 4 inches in rows. Birds can be a major headache, and will eat the tips of emerging seedlings. The best way to prevent injury is by covering rows with cheese cloth, Remay cloth or wire mesh raised slightly above the soil. Remove the protective covering soon after the seedlings have developed into the cotyledon or first leaf stage.
Apply a general garden fertilizer such as 10-30-10 at 2 to 3 pounds per 100 square feet at planting time. A second application in the same amount should be applied about four weeks later, when plants begin to flower. Organic sources can be substituted, along with compost, to reach a similar level of fertility.
Common pests of soybeans include the French bean fly, Chinese rose beetle, Southern green stink bug, and red spider mites. Of these, the French been fly is the most difficult to control, and may require a combinations of sprays, including neem with organic soaps such as Safers and Impede, while mites can be controlled with sulfur. Edamame has only a few disease problems. Heavy rain can create root rot from standing water, so plant in clean, well drained seed beds. Ideally, irrigate on a regular basis so there is an ample moisture supply at all times, although they can handle some stress.
Edamame is ready to eat in 65 to 70 days after planting, but there are also later maturing varieties. The whole plant is pulled out when the majority of the pods are well filled, but before the pods turn yellow. Cooking time will be influenced by the degree of tenderness. For more information on vegetable soybeans, check out the UH CTAHR website at ctahr.hawaii.edu/oc/freepubs/pdf/HGV-14.pdf.