Lettuces are often grown during winter and early spring to complete the chrysanthemum-tomato cycle, and they are a useful crop when a temperature of 10 to 16°C. (50 to 60°F.) can be maintained. One of the best varieties is Kordaat; another is May Queen and a third, the longer-established Cheshunt Early Giant.
Sow the seed in late autumn or early winter in boxes or pots in a temperature of 13°C. (55°F.) and when the seedlings have formed their second pair of leaves pot them up separately into 2-in. peat pots. When the roots show through the sides of the pots they can be planted out in the greenhouse border. A rich, well-drainedis best, for this is a crop which must grow and mature quickly. Space the plants 9 in. apart each way, and place them so that the top of the soil ball or the pot is slightly above the level of the surrounding soil. This helps to keep the leaves off the soil and the plants are less likely to be affected by botrytis. Water the plants in carefully to settle the soil around the roots, and afterwards at weekly intervals except when the weather is very dull or damp. Avoid wetting the leaves as this can lead to infection.
Lettuces can be started in the greenhouse and then planted out in a heated frame, successional sowings making it possible to harvest from December right through to when the earliest plants are ready in the garden. In a greenhouse when a border is maintained for, lettuce can normally be grown in this area until late March or early April.
In a greenhouse without a border, lettuces can be grown in pots – one to a 5-in. pot – but this is not a way in which many gardeners choose to use valuable space on the staging.