Cucumber, Pumpkin, Squash -Transplant Production & Transplanting
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 direct seeded 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 well developed 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, one 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 one 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”.
Transplanting cucurbits, plants can be grown 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 seed. It is best to use high quality, uniform, disease and insect free plants. Transplant size is critical to establishment success and plants should have no more than 2-3 true leaves at planting. Plants should be handled and planted carefully as all of the cucurbits are sensitive to transplant shock. Root replacement is slow so don’t crush or root prune plants. Plants can be hand or machine planted. Water the plant trays before planting and then water the field as quickly as possible after planting. Starter fertilizers with high phosphorus concentrations help to stimulate root re-growth. Newly transplanted fields should be watched closely and additional water should be provided to the plants if needed. This ensures good root growth out of the root-ball and more uniform establishment and plant growth.