Management Techniques for Bitter Melon at Each Stage of Greenhouse Cultivation

Bitter melon, also known as bitter gourd, is a plant in the Cucurbitaceae family, an annual climbing herb, edible and of high value, with fruits containing charantin.

Growing environment of bitter melon

Temperature

Temperature control: bitter melon prefers warmth, is fairly heat-tolerant and not cold-tolerant. Seed germination is suited to 30-35°C; below 20°C germination is slow, and below 13°C germination is difficult. At around 25°C, seedlings with 4-5 true leaves can be raised in about 15 days, whereas at around 15°C it takes 20-30 days. At 10-15°C bitter melon plants grow slowly, and below 10°C growth is poor; when the temperature is below 5°C, plants suffer markedly. However, slightly lower temperatures and short-day conditions advance the node at which the first female flower appears. The flowering and fruiting period is suited to above 20°C, with around 25°C being optimal. Within the range of 15-30°C, the higher the temperature, the more favorable it is for bitter melon growth and development —— earlier fruiting, higher yield and better quality. Above 30°C and below 15°C are both unfavorable for bitter melon growth and fruiting.

Light

Bitter melon is a short-day plant, fond of sunlight and not shade-tolerant. However, after long-term cultivation and selection, its requirements for day length are no longer very strict; but if light is insufficient during the seedling stage, its resistance to low temperatures will be reduced. In northern Hainan, when winter-spring bitter melon encounters low-temperature overcast and rainy weather, seedlings grow spindly and have poor stress resistance, and are often prone to cold damage — this is the reason. The flowering and fruiting period requires relatively strong light; sufficient light is favorable for photosynthesis and increases the fruit-setting rate; otherwise, flower and fruit drop is easily induced.

Water

Suitable soil: bitter melon prefers moisture but is not waterlogging-tolerant. During the growing period it needs 85% relative air humidity and relative soil humidity. In dry weather with insufficient water, plant growth is hindered and fruit quality declines. But water should not accumulate either; waterlogging easily causes root rot and yellowing and wilting of leaves, affecting fruiting in mild cases and causing disease and death of the plant in severe cases.

Nutrients

Bitter melon has a wide adaptability to soil, and can grow in soils from sandy loam to light clay loam. Generally it grows well and yields high on fertile, loose loam with strong water- and fertilizer-retention capacity. Bitter melon has relatively high fertilizer requirements; if organic fertilizer is sufficient, plants grow stoutly with luxuriant stems and leaves, bear more flowers and fruits, and the fruits are plump and of good quality. Especially in the later growth stage, if fertilizer and water are insufficient, plants become weak, flowers and fruits are few, fruits are small, bitterness intensifies and quality declines. Bitter melon needs relatively more nitrogen fertilizer, but nitrogen fertilizer should not be applied exclusively; otherwise stress resistance decreases, making plants susceptible to infection by pathogens and damage from cold. In fertile, loose medium loam, applying additional phosphorus and potassium fertilizer can make plants grow robustly and bear fruit without decline over a long period.

Management of bitter melon at each stage of greenhouse cultivation

1 Temperature and humidity management

On the basis of watering enough at transplanting, generally no watering and no ventilation are done during the seedling recovery period, keeping the daytime temperature in the greenhouse at 25°C-30°C and the nighttime at 14°C-18°C. After seedling recovery, normal management begins; by uncovering and covering the plastic film, the daytime temperature is maintained at 25°C-28°C, not exceeding 30°C, and the nighttime at 13°C-17°C, not lower than 12°C.

Entering the fruiting period, temperatures gradually rise and light becomes stronger, so management should focus on ventilation and cooling. Gradually increase the amount of ventilation and extend the ventilation time. In the high-temperature season, the film on both sides of the greenhouse should be rolled up to allow ventilation day and night.

2 Fertilizer and water management

Bitter melon is fertilizer-tolerant and not barren-tolerant. To ensure vigorous plant growth and improve fruit yield and quality, fertilizer must be applied reasonably. In the early fruit-setting stage, plants are small, grow slowly and need little fertilizer, so on the basis of sufficient basal fertilizer, no topdressing is needed. Intertillage and loosening the soil can be done to conserve moisture.

Entering the flowering and fruiting period, temperatures are higher, plant growth speeds up, and fertilizer and water demand increases. Also, because bitter melon has a long growing period and bears many fruits, timely topdressing must be noted to promote vines and protect fruits. In the early fruit-setting stage, generally water once about every 15d, and apply urea or ammonium sulfate with the water; urea at 4-5kg per 667m2, and ammonium sulfate at 8-10kg. In the middle and late fruit-setting stages, plant growth increases further, fruits expand quickly, transpiration is strong and water demand increases. Water can be applied once every 7-10d, and with the water apply 7kg each of potassium sulfate and urea per 667m2. In the high-temperature season, watering and fertilizing can be done in the morning and evening. In the later stage, to protect leaves and delay senescence, foliar sprays such as photosynthetic micro-fertilizer, Yemianbao, potassium dihydrogen phosphate, etc. can be applied.

3 Pruning and trellising

Bitter melon stems and vines grow luxuriantly, so greenhouse cultivation requires strict pruning. Bitter melon stem nodes easily produce adventitious roots; to expand the root absorption area, vines can be pressed before going up the trellis. The method is to open a shallow ditch about 15cm long and 3-4cm deep in the ground, bury a 15cm section of the lower part of the main vine into the soil, being careful not to bury or press the leaves. When the vine reaches 40-50cm, begin trellising, generally an A-shaped trellis with a height of 1.8-2m, and guide the vines onto the trellis. Bitter melon has luxuriant stems and leaves and strong branching ability. To make the vines distribute reasonably and grow and fruit normally, timely pruning is needed. After the main vine reaches a certain height, leave 2-3 side vines to climb the trellis together with the main vine, and remove all other side vines and their tendrils. After going up the trellis, for side branches that emerge later, if they have a fruit, keep the branch and immediately pinch off the top; if they have no fruit, cut off the entire side branch from the base. If there are 2 female flowers on branches at any level, the first female flower can be removed and the second female flower kept, because the fruit formed from the second female flower is of better quality than that from the first female flower. In the later growth stage, pruning may be omitted and growth allowed freely, but care should be taken to remove female-flowerless side vines, tendrils, excess female flower buds and lower old yellow leaves, and to strengthen ventilation and light penetration.

4 Artificial pollination

There are no insects to pollinate in the greenhouse, and female flowers often drop because they are not pollinated. Artificial pollination can prevent flower drop. The method is, before 10:00 a.m., take male flowers that opened the same day, remove the corolla, and smear the pollen shed by the stamens onto the stigma of the female flower.