How big should tomato seedlings be before transplanting them?

Tomato seedlings at a seedling age of 20—25 days, when the seedlings have 3—4 leaves, can be transplanted, and this is the suitable period for planting out. It should be noted that tomatoes are not moved during the seedling-raising period; planting out large seedlings causes severe root damage, and if leggy growth occurs during the seedling stage, 1-2 sprays of chlormequat should be applied in time. Below is an introduction to the transplanting and planting-out management methods for greenhouse tomato seedlings.

1. Land preparation and planting out

Before transplanting, install shade-type greenhouse film, open it around the sides and leave only the upper part to prevent rain and strong light. After installing the film, make the planting beds into high, level beds 100 cm wide or ridges 50 cm wide, apply base fertilizer well while making the beds, and irrigate to full moisture content. When two fruit trusses are to be retained, the planting spacing is 25 cm; when 3 fruit trusses are retained, the spacing is 30 cm, planting about 4,500 plants per 667 m.

2. Management after planting out

After planting out, ventilate heavily day and night, ventilate from the bottom, close the sides of the greenhouse, and ventilate only from the upper middle part. When the outside temperature drops below 15°C, stop ventilating at night, keep the daytime temperature at 25—30°C and the nighttime temperature at 15—17°C; 2—3 days after planting out, when soil moisture is suitable, cultivate and loosen the soil in time, and build up the ridges while loosening the soil. After the seedlings recover, water once, and thereafter water sparingly to prevent leggy growth; use single-stem pruning, keep 3—4 well-shaped fruits per fruit truss, and for small-fruited varieties keep 4—5 fruits, removing the remaining fruits.