How to Grow Cowpeas for More Pods: Practical Tips Explained
Cowpea (Vigna unguiculata), also called yardlong bean, is a vegetable abundant in summer. It belongs to the cultivated species of the cowpea species that can form long pods, an annual twining herbaceous plant. Also known as cowpea, long-horn bean, belt bean, and kelp bean. It contains various vitamins and minerals, etc. The tender pods are thick and fleshy, crisp and tender when stir-fried, and can also be blanched for cold salads or pickled. The pods are long and tube-like, crisp in texture yet soft, with common types including white cowpea, green cowpea, and purple cowpea. When selecting cowpeas, generally those with uniformly thick pods, bright color, translucent gloss, and plump seeds are best, while those with cracks, wrinkled skin, overly thin pods without seeds, or insect marks on the surface should not be purchased. Cowpea has excellent nutritional content and is the meat among vegetables.
The growing environment of cowpea
Cowpea has weak root regeneration, so direct sowing is mostly used. The suitable germination temperature is 25-30°C, and the air temperature at sowing should be above 20°C. ① Before sowing, the potting soil should be watered thoroughly, with 3-4 seeds per hole, covered with about 2-3 cm of soil. ② After germination, thin out diseased and weak seedlings, keeping 2-3 plants per hole; when there are 3-4 true leaves, thin again, keeping 1-2 plants per hole. If transplanting is needed, 3-4 weeks after germination, when 2 true leaves have grown and the first compound leaf has unfolded, they can be planted out, then watered thoroughly, and after surviving, normal management begins. Plant out after the last frost, with a seedling age of 20-25 days. The planting field should be given more decomposed organic fertilizer, 3000-5000 kg per mu, 25-30 kg superphosphate, 50-100 kg plant ash or 10-20 kg potassium sulfate. Planting density: row spacing 66 cm, hole spacing 10-20 cm, 3000-3500 holes per mu (when raising seedlings, the two-or-three-plant method can be used to facilitate later planting out). After planting out, water to help the seedlings recover, then cultivate deeply to control growth for 5-8 days to promote strong root development. When there are 5-6 true leaves, supports should be set up. In the early stage, the vines should be guided onto the supports counterclockwise and fixed with string, generally done at noon or in the afternoon on a sunny day; in the later stage, the twining ability is very strong and no manual assistance is needed.
Fertilization in the early stage should be light. After the plants survive planting out, apply 1 application of thin decomposed organic fertilizer. From bud appearance to the mature stage, fertilize once every 7-10 days, taking care to increase phosphorus and potassium fertilizer. For the proportion of potassium fertilizer, apply continuously 2-3 times. It is warm-loving, with an optimal growing temperature of 20-30°C; growth is slow below 15°C, and frost damage occurs below 5°C. It is heat-tolerant and can still flower and set pods at 35°C, but the quality is poor. It is relatively drought-tolerant but not waterlogging-tolerant. In the early stage, water should be properly controlled. When about half of the flower clusters on the main vine begin to set pods, water fully to keep the soil moist.
When the main vine grows its first flower cluster, all lateral branches below the cluster should be removed, and lateral branches above the cluster should be pinched, leaving 2 leaves at the base; when the main vine has climbed all over the supports, pinch the top to encourage flower buds to sprout on the lower lateral branches. The inflorescence is a raceme with 2-5 pairs of flowers, but often only 1 pair of pods is set; usually only after the first pair of pods is picked do the second pair of flower buds begin to develop or set fruit; if fertilizer and water are sufficient and care is appropriate, all flowers on the inflorescence can set pods. It sprouts easily, and seed soaking is generally not needed. The bottom soil for raising seedlings should be firm, best with 6 cm of loam spread on top, to prevent deep penetration into the soil, as root damage during transplanting would be great. Therefore, when the seedlings have one pair of true leaves, they can be transplanted with soil, and large seedlings are not suitable for transplanting. If conditions permit, nutrient pots or plug trays can be used for raising seedlings, with two or three seedlings per pot. Plant out after the last frost, with a seedling age of 20-25 days. The planting field should be given more organic fertilizer. Planting density per mu is 6 spacing 1 per mu; after planting out, water to help the seedlings recover, then cultivate deeply to control growth for 5-8 days to promote strong root development. After the last frost, the density for open-field varieties is row spacing 66-70 cm and plant spacing 25-30 cm. After sowing, firm the soil with your feet so that the soil and seeds are fully settled.
Cowpea is difficult to manage, as many vegetable growers know. It tends to grow excessively and set pods poorly, and even flower and pod drop often occur. So what exactly causes the difficulty in setting pods? How should it be managed to set more pods?
1. Planting density should be reasonable. The best seedling age for planting out cowpea is when the young leaves have just unfolded. A reasonable row spacing for cowpea is generally 60 cm for the small rows and 80 cm for the large rows, with support height 1.8-2 m. The taller the supports, the greater the row spacing should be, and plant spacing is about 45 cm, generally with two plants planted together. If the planting density is too high, it will cause excessive vegetative growth and make pod setting difficult.
2. Day-night temperature difference must be controlled. Cowpea is highly heat-tolerant but not cold-tolerant, with a suitable growing temperature of 20°C-25°C. During the flowering and pod-setting period of cowpea, the daytime temperature, nighttime temperature, and day-night temperature difference should be well controlled. The more suitable growing temperature during the flowering period of cowpea is that the daytime temperature should not exceed 30°C and the nighttime temperature should not exceed 18°C. Therefore, cowpea growers are reminded to manage the time of closing the greenhouse well, delaying the closing time as the temperature rises. The standard for closing the greenhouse during the flowering and pod-setting period of cowpea is when the greenhouse temperature reaches 17°C.
3. Light conditions should be suitable. Although the cowpea varieties suitable for greenhouse cultivation do not have strict requirements for light hours, they have relatively high requirements for light intensity. Especially during the flowering and pod-setting period, insufficient light will cause flower and pod drop in cowpea.
4. Soil moisture and nutrients should be appropriate. Watering time and amount should be flexibly controlled according to local soil moisture conditions. Throughout the entire growing period of cowpea, at the most basic level, three waterings should be done: the first watering after planting out, which must be thorough, otherwise the plants will be uneven; the second watering when the vines grow to 0.6 m high; the most critical point in cowpea production is to water the plant but not the pods, and watering is not suitable during the full flowering period of cowpea, so the third watering should be done before the initial flowering stage, and combined with watering, spray a flower-promoting and fruit-preserving agent, which is more conducive to cowpea flowering and pod setting. After pod setting, water lightly once more to promote pod expansion and elongation. In addition, nitrogen fertilizer should not be applied one-sidedly, otherwise it will cause excessive vine and leaf growth and delay flowering and pod setting. Phosphorus fertilizer should be increased to promote the formation of root nodules and enhance their nitrogen-fixing ability.