Melon - Transplant Production & Transplanting
For areas of Utah with shorter growing seasons, we recommend transplanting early melons. Mainseason melons are also seeded for mid- to latesummer production. Very few growers direct-seed triploid watermelon because seeds are expensive and germination and early growth is slow, particularly under cooler soil conditions. Transplants can be started on-farm or purchased.
For starting transplants, sow melon seeds into plastic plug trays with 50, 72, or 128 cells per tray filled with a good soilless mix. Adequate light and temperature management are both essential to produce a quality plant. Greenhouse temperatures should be approximately 75°F during the day and 65°F at night. After approximately 4-5 weeks, melon transplants should have 2-3 mature leaves and a well-developed root system before setting in the field.
Growing seedless watermelon transplants requires a bit more finesse. Since seedless types are less vigorous, slow to germinate, and emerge erratically, early temperature management after seeding helps improve establishment and uniformity. After seeding and watering the plug trays, expose the seeds to 85-90°F temperature conditions for 36-40 hours, but no longer. You can do this in a dark room with the trays stacked on top of each other, or use heating pads if only a few trays are needed. Move seeds to cooler growing temperatures after emergence. Longer exposure to high temperatures results in elongated hypocotyls which make the plants grow tall and leggy. These seedlings are then difficult to handle and transplant.
Water regularly and feed twice weekly with a soluble complete fertilizer diluted to 100 ppm nitrogen after the seedlings emerge. Brushing the plants each day one week before planting helps strengthen the stem. Brushing should be done when the leaves are dry to minimize disease transfer. Transplants can also be hardened or conditioned by exposing them to wind and cooler temperature to make the plants stocky and strong. Condition or “hardened off” transplants for a short time each day by exposing them to cool temperatures (60-65 °F) starting one week before transplanting
Melons can be transplanted in bare soil or through plastic mulch. Transplants are used for early production, when market prices are high, and to decrease seed costs for expensive hybrid or seedless melons. It is best to use high quality, uniform, clean plants. Transplant size is critical to establishment and plants should have no more than three leaves at planting. Plants should be handled and planted carefully, as melons are sensitive to transplant shock. Root replacement in melons is slow, so don’t crush the root ball. Plants can be hand or machine planted. Water the plants before and after planting. Starter fertilizers with high phosphorus concentrations helps to stimulate root re-growth. Newly transplanted fields should be watched closely and watered if needed. This ensures good root growth out of the root ball and uniform plant growth.
To produce seedless watermelon, it is important to understand that triploid (seedless) watermelon flowers do not produce enough pollen to adequately pollinate themselves. Therefore, another source of pollen must be available to achieve acceptable levels of fruit set. A diploid (seeded) cultivar planted within the crop can serve as the pollenizer (Variety Suggestion Melon Table).
Research suggests that 25-33% of the plants in the field should be diploid (seeded) to produce enough pollen for good fruit set in the seedless crop. You can accomplish this by planting the pollenizer between every third and fourth triploid plant within the row. First plant your seedless crop at your normal in-row spacing, then come back and plant the pollinizer periodically down the row. By planting the pollinators in-row rather than having a dedicated pollen row in the field, you increase the number of triploid plants and the yield of seedless watermelons harvested per acre. These pollenizer cultivars commonly have non-marketable fruits, may be all male plants (pollen producing only), or may produce mini- or palm-sized fruits. If you have a market for the seeded fruits, make sure the seeded and seedless watermelons look different from each other at harvest so they are not mixed before going to market.