Early-Spring Low-Tunnel Cultivation of Zucchini: High Yield and High Quality

Zucchini, also called American pumpkin, originated in the tropical regions of the Americas. It is a warm-season vegetable that also tolerates low temperatures and has strong adaptability to temperature, making it one of the main cultivated vegetables in northern China. Did you know? Cultivate early-spring low-tunnel zucchini this way for high yield and high quality!

1. Sowing Time for Early-Spring Greenhouse Zucchini

For early-spring greenhouse cultivation of zucchini, the suitable sowing period depends on the air temperature at transplanting time, the degree of low-temperature tolerance of the zucchini variety, and the heat-retention performance of the greenhouse. Zucchini must be transplanted when the soil temperature inside the greenhouse is stably above 11°C and the nighttime air temperature is above 0°C. Once the safe transplanting period is determined, counting back 30——35 days from the transplanting date gives the suitable local sowing period for zucchini. In the Yangtze River basin, when cold beds are used for seedling raising, the sowing period for zucchini is generally from late January to early February. When plastic greenhouses with inner low tunnels are used as seedling-raising facilities, sowing can be advanced to December to early January, with seedlings raised on electric heating beds or fermented manure heating beds.

2. Preparation of Nutrient Soil

Mix 6 parts fertile, loose garden soil with 4 parts decomposed organic fertilizer, leave the mixture piled for more than one month, then sieve it, and add 5——10 kg of nitrogen-phosphorus-potassium compound fertilizer per cubic meter of nutrient soil. The nutrient soil should be disinfected with formaldehyde or carbendazim, etc. After thorough mixing, fill it into plastic nutrient pots or paper bags.

3. Seed Treatment

Before sowing, first select the seeds with clean water (soak for about 20——30 minutes), remove the inferior seeds floating on the surface, then soak them in hot water at 55°C for 5——10 minutes. After natural cooling, continue soaking for 2——4 hours. Remove, air-dry, and then either sprout them before sowing or sow directly.

4. Sprouting and Sowing

For seeds that need sprouting, wrap the treated seeds in a wet towel and place them in a 25——30°C environment to sprout. During sprouting, rinse the seeds once a day in warm water, drain the water, and continue sprouting. Generally after 2——3 days, when the sprouts are 0.2——0.4 cm long, they can be sown. Before sowing, first check the moisture of the nutrient pots. If they are rather dry, water appropriately. Place the sprouted seeds flat in the nutrient pots that have been pre-punched with small holes, 1 seed per pot, and never insert them upright. After sowing, cover with fine soil 1——2 cm deep, cover with plastic film, set up low tunnels, and close the greenhouse to retain heat and moisture.

5. Seedling-Stage Management

After sowing and before emergence, the temperature inside the shed should be maintained at 25——30°C during the day and 18——20°C at night. Be careful to cover with plastic film, straw curtains, and other coverings to retain heat. After 3——4 days, the seedlings emerge one after another; remove the plastic film and lower the temperature appropriately. Keep the seedbed temperature at 20——25°C during the day and 10——15°C at night, with appropriate ventilation. From the unfolding of the first true leaf until 10 days before transplanting, raise the daytime temperature to 22——28°C, lower the nighttime temperature to 8——13°C, and keep the soil temperature above 15°C. Begin ventilation hardening 10 days before transplanting, maintaining 15——22°C during the day and 8——15°C at night.

Generally no watering is done before emergence. If the seedbed is too dry after emergence, water appropriately on sunny days. When the first true leaf unfolds, apply one foliar topdressing of monopotassium phosphate at a concentration of 0.3%——0.5%. After watering, pay attention to ventilation to reduce air humidity.

When the seedling age is about 30 days, with 4——5 true leaves, a seedling height of 25 cm, and a stem diameter of 0.5 cm, they can be transplanted. Zucchini seedling raising can also use grafting, with Yunnan black-seed pumpkin or “901” as the rootstock. Rootstock seeds are sown 2——3 days earlier than scion seeds, and the approach grafting method is used.

6. Land Preparation and Base Fertilizer Application

Choose a loose, fertile plot that has not previously grown crops of the same family as zucchini to build the shed, and apply sufficient base fertilizer. Generally, apply 3000——3500 kg of decomposed organic fertilizer per mu. After deep plowing and land preparation, apply 150——200 kg of bio-organic fertilizer or 100 kg of cake fertilizer in furrows. Cover the shed about 15 days before transplanting, and keep it sealed after covering to raise the soil temperature. At 3——5 days before transplanting, prepare the land and make beds. For double-row planting, the bed width is 1.5 m (including the ditch); for single-row planting, the bed width is 1.0 m (including the ditch).

7. Transplanting

When the temperature inside the shed is stably above 12°C, the 10 cm soil temperature is 12——15°C and has remained stable for about 1 week, transplant on a sunny morning at the end of a cold spell and the beginning of a warm one. In the Yangtze River basin, when transplanting with a large shed over a small tunnel, the transplanting period can be mid-to-late February; when using a medium shed or low tunnel, the transplanting period is early March. If the soil in the greenhouse is rather dry, water the holes first before transplanting. After the water infiltrates, gently move the seedlings into the holes, then fill with soil so that the surface of the nutrient pot is level with the bed surface. If the soil moisture is suitable, transplant directly into the holes. For double-row transplanting, the plant spacing is 0.7——0.8 m; for single-row transplanting, the plant spacing is 0.6——0.7 m. After transplanting, immediately cover with plastic film. Cut a small opening with a blade at the planting spot, gently pull the seedling out, and seal the film opening with soil. Where low tunnels are added, set up the tunnel frame and cover with film immediately after transplanting, and add straw curtains and other insulation at night.

8. Field Management

1. Temperature management: Immediately after transplanting, seal the greenhouse to retain heat, maintaining 28——30°C during the day and 15——20°C at night, preventing low temperatures below 0°C. In case of low temperatures, add straw curtains or use multi-layer plastic film covering. Where low tunnels are set up inside the greenhouse, uncover the low-tunnel film during the day and cover it tightly again at night. After the seedlings recover, lower the temperature appropriately, maintaining 22——25°C during the day and 12——18°C at night. At 4——7 days after transplanting, maintain 25——28°C during the day and about 15°C at night. When the temperature rises above 30°C, ventilate. At noon on sunny days, uncover the skirt edges for ventilation, and open the vents gradually from small to large. After late April, the low tunnels inside the greenhouse can be removed, and even the greenhouse skirt edges can be removed.

2. Fertilizer and water management: For zucchini transplanted with plastic film mulching, there is generally no need to water for seedling recovery. Where no plastic film is laid, water once within 2——3 days after transplanting to help the seedlings recover, with the amount of water just enough to soak through the nutrient soil, not too much. Afterward, water according to plant growth and soil moisture. For cultivation with plastic film mulching, furrow irrigation can be used, but drip irrigation is best, combined with topdressing.

Generally, the first topdressing is applied during the fruit-swelling stage of the first batch of fruit, with 15——20 kg of compound fertilizer per mu. The second topdressing is after the first batch of fruit is harvested and during the fruit-setting stage of the second to third batches of fruit, with 8——10 kg of compound fertilizer or 6——7 kg of urea per mu. Afterward, topdress according to plant growth.

3. Flower and fruit retention: Early-spring greenhouse cultivation of zucchini must use artificial supplementary pollination or treatment with plant growth regulators. For artificial supplementary pollination, at 8——9 a.m. each day, pick freshly opened male flowers, remove the petals, and gently dab the pollen from the stamens onto the stigma of the female flowers. If plant growth regulators are used, when the female flowers open, spray the whole plant foliage with zucchini fruit-setting essence without pollination.

4. Other management: Timely remove diseased leaves, old leaves, side branches, and tendrils. Where no plastic film is used, after the seedlings recover, cultivate and loosen the soil in time, and after watering for seedling recovery, cultivate 2 more times in succession. After cultivation, begin seedling hardening, that is, appropriately controlling water.

9. Harvest

Zucchini should be harvested as young fruit. Generally, fruit can be harvested 10——12 days after flowering. The first fruit at the base should be harvested early to supply young fruit to the market. After entering the peak fruiting period, harvesting can be appropriately delayed. The most suitable harvest time is after the morning dew has dried, and harvesting around noon should be avoided.