Transplant Production

Cucumber, Pumpkin, and Squash

Some growers transplant cucumbers and summer squash, particularly, for early production or when planting in high tunnels. Transplants work well in most areas of Utah with shorter growing seasons. Most cucumbers, winter squash, and pumpkins are directseeded for mid-to-late summer production periods. Growers can produce their own transplants, or plants can be purchased from a local greenhouse operation. Sow cucumber seeds into plastic plug trays with 72 or 128 cells per tray filled with a good soilless mix. Sow summer squash seeds into larger plastic plug trays with 50 or 72 cells per tray filled with a good soilless mix. Adequate light is essential to produce a quality plant but temperature management is critical if quality transplants are to be produced.

Greenhouse growth temperatures for cucurbits should be approximately 75 °F during the day and 65 °F at night. Allow 4-5 weeks to grow transplants depending on greenhouse growing temperatures. All cucurbit transplants should have 2-3 mature leaves and a welldeveloped root system before transplanting to the field. After seeding and watering the trays, expose the seeds to 85-90 °F temperature conditions for 30-40 hours. 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. Higher tray temperatures after seeding helps create conditions for more uniform germination and plant stands. However, do not allow the seeds to emerge in high heat conditions. Longer exposures times (+48 hrs.) to high temperatures result in elongated hypocotyls which make the plants grow tall and leggy. These seedlings are then difficult to handle and transplant.

Once seedlings emerge, water regularly and feed twice weekly with a soluble complete fertilizer diluted to 100 ppm nitrogen. Brushing the plants each day, 1 week before planting, helps strengthen the stem. Brushing should be done when the leaves are dry to minimize disease transfer. Transplant can also be hardened or conditioned by exposing them to wind and cooler temperature to make the plants stocky and strong. Condition or “harden off” transplants for a short time each day by exposing them to cool temperatures (60-65 °F) starting 1 week before transplanting. Avoid exposing plants to temperatures that are less than 55 °F. Don’t over-condition or overharden the plants as this will delay establishment and plants will be slow to start growing again. For more details on growing high quality plants, refer to the USU extension publication “Vegetable Transplant Production.”

Melons

For areas of Utah with shorter growing seasons, we recommend transplanting early melons. Main-season melons are also seeded for mid- to late-summer 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 1 week before transplanting.