Seedlings can be transplanted when they have 5-6 leaves. Water the rows the day before transplanting.
Transplant at the 5-6 leaf stage allowing a minimum of 25x38cm (10x15in) between plants. The soil should be firm and contain plenty of well rotted compost etc, preferably from a previous crop, it should also be well limed. Just before planting, rake in 3oz/sq yd of a balanced fertiliser.