If you wait for the soil to warm up before sowing tender crops, the plants will just produce leafy growth and little or no crop, so they must be started off under protection. Most tender vegetables hate root disturbance, so sow them in individual small pots. Plants that start growing in a greenhouse, polythene tunnel or on a kitchen windowsill must have two to three weeks of hardening off before being transplanted into the garden soil. If you buy your young plants from a garden center or nursery, they should have already been hardened off, but it is worth checking. Here are some plants and their requirements:
- Aubergines, peppers and tomatoes can be moved outside to grow successfully when the soil temperature reaches 50°F (10°C).
- Courgettes, marrows and squashes can all be grown outside, but generally tend to do better in a cold-frame or polythene tunnel. They prefer high humidity and may suffer from mildew if grown outside in dry conditions. Transplant them with minimum root disturbance, as even slight damage to the roots can result in rotting and, eventually, the loss of the plant.
- Young plants of sweetcorn should be about 6 to 8 inches (15–20cm) high before they are planted out. Transplant them in their moist peat pots into square or rectangular blocks (as they are pollinated by wind), with the plants spaced 14 inches (35cm) apart, with 14 inches (35cm) between rows.
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Vegetables started in greenhouses need two or three weeks before going into garden soil.
