Option 2. Transplanting
Sow seeds in small plastic pots or containers using a potting mix that has good water-holding capacity and good drainage such as peat moss, commercial potting soil, or a potting mix prepared from soil, compost, rice hull, and vermiculite or sand. Plant two or three seeds per container and thin to a single seedling when they have four to six true leaves. Water the seedlings thoroughly every morning to maintain a moist but not wet soil. Seedlings are ready for transplanting 15-20 days after sowing or when they are 10-15 cm tall.
Bare-root plants will not survive so pull seedlings with their root balls intact before transplanting.Transplant seedlings into the field at spacings similar to those used for the direct seeding method.
Staking and Trellising (Balag)
Bitter gourd grows very fast and vines elongate rapidly within two weeks after planting. Thereafter, the plant sends out lateral stems. Staking and trellising will increase fruit yield and size, reduce fruit rot, and make spraying and harvesting easier.
There are several methods of trellising bitter gourd. At AVRDC, bamboo poles, wood stakes, PVC pipes or other sturdy material are used to provide support and keep the fruit and foliage off the ground. The trellis is arranged either in a lean-to or tunnel structure. The trellis should be 1.8–2.0 m high, constructed from stakes 1.2–1.8 m apart, which is almost similar to the plant row spacing.
For the lean-to type, the stakes are joined between two adjoining beds forming an A-shape structure (Figs. 4, 5). Horizontal stakes are installed at the top joining all other beds. The stakes support the climbing vines and lateral stems. Strings are used to secure adjoining stakes. Plantings are easier to manage and more productive when 2-m-high rather than 1-m-high string trellises are used.
For the tunnel type, plants are grown inside an arch-shape structure made of either PVC or galvanized iron pipe (Fig. 6). Plants are supported by bamboo stakes where vines freely climb and reach the top. The vines and lateral stems will then grow along the structure.
Another type of trellising consists of a system of vertical strings running between top and bottom of horizontal wires, or horizontal wires running across all directions on top as shown in Fig. 7.
Bitter gourd develops many side branches that are not productive. To improve yield, remove lateral branches until the runner reaches the top of the trellis. Leave 4-6 laterals and cut the tip of the main runner to induce early cropping. Removal of lateral branches in the first 10 nodes has a positive effect on total yield. Without pruning, most of the female flowers occur between the loth and 40* nodes, or at a height of 0.5-2.0 m.
Bitter gourd requires a balance of nutrients from organic and chemical fertilizers. Fertilizer application rates depend on soil type, fertility level, and soil organic matter. In sandy soils at AVRDC, fertilizer application consists of a basal application followed by four sidedressings, providing a total of 184 kg N, 112 kg P2O5 and 124 kg K2O per ha (Table 1). In clay or heavy texture soils, the entire amount of P, and one-third of N and K is applied before planting, either by broadcasting and tilling or by banding a few cm deep and to the side of the plant row in the bed. The balance of N and K is applied in two or more sidedressings.
No matter the soil type, the first sidedressing is applied when plants have four to six true leaves. Subsequent sidedressings are applied at two-week intervals. Compost or manure can be used to satisfy the basal application of organic fertilizer.
Bitter gourd will not tolerate drought. Maintain good soil moisture in the upper 50 cm of soil where the majority of roots are located. At AVRDC, fields are furrow-irrigated every 10 days during the cooldry season, and weekly during the hot-dry season. During the rainy season, drainage is essential for plant survival and growth. In water-limited environment, trickle or drip irrigation is an efficient method of supplying water and nutrients to bitter gourd plantings.