When is the best time to sow greenhouse watermelons?

Greenhouse watermelon is a commonly used method of growing watermelons, and many growers use this method to grow watermelons, so when should greenhouse watermelons be sown?

1. Planting time of greenhouse watermelons

The sowing time of greenhouse watermelons is related to the growing technique and the watermelon variety. For three-film seedling raising, sowing generally starts on January 10; for four-film mulching, sowing generally starts on December 20; for open-field watermelons, seedling raising generally starts on March 10.

Before sowing, the seeds also need to be soaked and sprouted. Sun the seeds for 2 days, then disinfect the seeds. Soak the seeds in 55°C warm water, stirring while soaking for about 30 minutes; after cooling, continue soaking for 2 hours.

For chemical treatment, usually soak the seeds in 100-fold formalin solution for 30 minutes, or soak them in 500-fold 50% carbendazim solution for 1 hour, then rinse them clean with water and soak for 3-4 hours. Wash the treated seeds clean, place them in a constant-temperature chamber at 40°C for 6 hours of high-temperature sprouting, then sprout them at a constant 33°C. When the radicle grows to 0.5 cm, they can be sown.

2. Growing techniques for greenhouse watermelons

1. Land management

Greenhouse watermelons are generally planted at a relatively high density, so the land should be prepared carefully. For greenhouses left idle in winter, deep plow 25 cm before winter and allow the soil to freeze into clods, making the soil loose.

Generally, apply 4000-5000 kg of high-quality barnyard manure or 3000-4000 kg of fully decomposed chicken manure, 50 kg of superphosphate, 15-20 kg of potassium sulfate, and 100 kg of fully decomposed cake fertilizer per mu as base fertilizer.

Spread half of the base fertilizer evenly over the whole area and then plow it into the soil. After leveling the land, open furrows and apply the other half of the base fertilizer. Generally, small high ridges and high beds are used for cultivation, making beds at a row spacing of 1-1.2 m. Under the conditions of dense planting with supports, grafted cultivation, two-vine pruning, and leaving 1 fruit per plant, make small high ridges at a row spacing of 1 m. When using horizontal ground cultivation, beds can be made in a north-south direction (parallel to the longitudinal direction of the greenhouse).

2. Transplanting

When covered with 3 layers of film, greenhouse watermelons should be planted about 10 days earlier than double-film arch shed cultivation, at a density somewhat greater than that of double-film arch shed cultivation, and careful pruning is required. Cultivation with dense planting and supports should be denser than horizontal ground cultivation.

3. Temperature and light

Temperature: 5-7 days after transplanting greenhouse watermelons, pay attention to raising the ground temperature. If the daytime temperature inside the greenhouse is higher than 35°C, measures should be taken to shade and cool it. After the seedlings recover, ventilation can begin to regulate the temperature inside the greenhouse. Generally at this time, the daytime temperature inside the greenhouse should not be higher than 32°C, and the nighttime temperature should not be lower than 15°C.

When the vines grow to about 31 cm, the small arch shed inside the greenhouse can be removed. During the full flowering period of greenhouse watermelons, sufficient light and a relatively high nighttime temperature should be maintained, because if the nighttime temperature is relatively low after artificial pollination, it will affect watermelon expansion and cause fruit drop. When the outside temperature exceeds 18°C, ventilation should be increased, opening the skylights and both sides of the greenhouse at the same time for ventilation, so that the daytime temperature inside the greenhouse is not higher than 30°C, preventing too large a day-night temperature difference, which would cause the watermelon flesh to become poor in texture and reduce quality.

Light: regulation of gas composition inside the greenhouse. Under closed greenhouse conditions, the carbon dioxide content in the air is seriously insufficient, affecting the normal progress of photosynthesis and the accumulation of assimilates. Applying carbon dioxide gas fertilizer can increase the carbon dioxide concentration inside the greenhouse and supplement the carbon dioxide content inside the greenhouse.

Increase the amount of light received. Watermelons require relatively strong light. However, due to condensation or dirt on the surface of the greenhouse film, the light intensity inside the greenhouse is often reduced, especially under multi-layer covering. Therefore, care should be taken to keep the greenhouse film clean, and old films with poor light transmittance should not be used.

4. Pruning and pollination

When watermelons grow to a certain extent, pruning, trellising, and vine tying should be carried out, and then artificial pollination should also be done, so that the watermelons can grow healthily.

5. Topdressing and watering

During the watermelon growing period, topdressing and watering should be carried out reasonably. In the early stage of greenhouse watermelons, the amount of watering should not be too large. After the seedlings recover, if the soil is not dry, watering can be skipped; if it is too dry, water thoroughly once along the furrows.