Bitter melon grown in greenhouses can achieve early maturity

Bitter melon, also known as balsam pear, is a plant of the Cucurbitaceae family and an annual climbing herb. The stems, branches, petioles and pedicels are covered with soft hairs, with axillary tendrils. The leaves reach 3 to 12 cm in diameter, with 5 to 7 palmate deep lobes, the lobes elliptical with serrated outer edges. It flowers at the turn of spring and summer, is monoecious, and yellow. The fruit is oblong-elliptical, with most of its surface covered in irregular wart-like protrusions. The seeds are hidden within the fleshy fruit, and when mature are wrapped in a red aril. Bitter melon is a vegetable people love to eat; its place of origin is unclear, but it is generally believed to be native to tropical regions. It is widely cultivated in South Asia, Southeast Asia, China, and the Caribbean islands.

Bitter melon likes warmth, is relatively heat-tolerant, and is not cold-tolerant. Seed germination is suited to 30-35°C; when the temperature is 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 grown 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, the plants are significantly damaged. However, slightly lower temperatures and short-day conditions cause the node of the first female flower to appear earlier. 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's growth and development——fruiting early, with high yield and good quality. Above 30°C and below 15°C are both unfavorable for bitter melon's growth and fruiting.

Bitter melon grown in open fields takes about 6-7 months to reach the market, while greenhouse cultivation can bring it to market more than 1 month earlier. So how can bitter melon be grown in greenhouses to achieve early maturity? Below we introduce exactly how to do it.

1) Variety selection. Excellent bitter melon varieties suitable for greenhouse cultivation include: Sichuan Changbai bitter melon, Hunan Lanshan bitter melon, Jiangxi Yangzizhou bitter melon, Ji'an white bitter melon, etc.

2) Raising strong seedlings. In early to mid-January, raise seedlings in electric heating beds inside the greenhouse, using nutrient pots to protect the roots. Bitter melon seeds have a hard, turtle-shell-like shell, so they need to be rinsed with boiling water or warm water; stir until it is no longer too hot to touch, then soak at room temperature (around 25°C) for 24-28 hours, remove, wash, wrap well, and germinate at 30-35°C for 7-10 days until sprouting. Each 667 sq m (1 mu) of greenhouse requires about 200 grams of seed.

3) Transplanting. In mid-to-late February, when the seedlings have 4-5 leaves, transplant them onto high ridges 1.2 m wide including the ditch, planting 1 row, with a plant spacing of 0.5 m, planting 1100 plants per 667 sq m.

4) Management after transplanting

① Temperature control and humidity adjustment in the greenhouse. After transplanting, during the seedling recovery period, keep the greenhouse closed to raise the temperature and promote recovery. Before the end of March, keep warm and prevent freezing, with appropriate ventilation during the day. Before the end of April, pay attention to keeping warm at night and ventilating to reduce humidity during the day. After May, focus on ventilation to cool down and remove moisture; start ventilation when the midday temperature reaches 30°C, and stop ventilation when the temperature inside the greenhouse drops to 25°C in the afternoon. In June, remove the bottom skirt film of the greenhouse, keeping the roof film to protect against rain.

② Fertilizer and water management. Bitter melon likes fertilizer and moisture; under conditions of sufficient water and fertilizer, yields are high and quality is good. On the basis of applying sufficient base fertilizer, fertilizer and water management must also be strengthened. Although bitter melon is tolerant of fertilizer, its tolerance is weak at the seedling stage, and slightly concentrated fertilizer will burn the seedlings, so topdressing should be light early and heavy later. During the seedling recovery period after transplanting, 10% dilute manure water is sufficient; during the vigorous growth period of stems, vines and leaves and during the flowering and fruiting period, apply 1-2 heavy fertilizer applications, each time applying 25-30 kg of compound fertilizer per 667 sq m, and thereafter, after each harvest, apply a topdressing of a mixture of 0.2% urea and 0.3% monopotassium phosphate once. The characteristics of water management are: after seedling recovery, during the early growth stage, water can be appropriately controlled to keep the soil moist. During the rainy season, clear the ditches in time for drainage.

③ Pruning and trellising. Bitter melon has strong branching; greenhouse cultivation with high density is even more prone to overly dense vines and leaves, poor ventilation and light penetration, wasted nutrients, and effects on yield and market quality. Therefore, pruning must be strengthened, and trellis cultivation should be used. When tendrils emerge from the vines, promptly set up A-shaped, arched, or trapezoidal trellises and guide the vines onto them. Bitter melon mainly sets fruit on the main vine, so side vines should be removed; under conditions of sufficient water and fertilizer, a few side vines can also be retained later to increase late-season yield. At the same time, during the mid-to-late production period, old leaves and diseased leaves should be removed at any time to facilitate ventilation.

④ Artificial supplementary pollination. Because early-maturing cultivation of bitter melon occurs at low temperatures, the greenhouse door is opened less, air movement inside the greenhouse is small, and there are few insects to pollinate, so natural pollination is difficult. Therefore, artificial pollination is needed, and 20-40 mg/L of 2,4-D should be applied to the female flower pedicel or young fruit to increase the fruit-setting rate of bitter melon, overcome fruit abortion, promote fruit expansion, and increase yield.

5) Harvesting. Bitter melon is eaten as a tender fruit, and should be harvested promptly 12-15 days after flowering. Generally, the appropriate harvest time is when the fruit has fully grown and the corolla begins to dry up. Greenhouse early-maturing cultivation begins to reach the market in mid-to-late April, with a yield of 2500 kg per 667 sq m, and considerable economic benefit.