It is possible to grow your own lettuces throughout the year by careful planning and selection of the right varieties.
Classification is by the season of harvesting and not that of sowing.
These can be first sown outdoors in early spring followed by a succession of sowings every two weeks. This will give a supply of lettuce from early summer through to the end of autumn. Select either cabbage, cos or American varieties or have a mixture to give a varied crop this also has the advantage of varying speeds of germination and growth, leading to an extended harvesting period
However, this routine of successional sowing does always give an uninterrupted supply. The varying weather conditions give rise to problems if the temperature drops then the crop is checked and growth is slowed down and in hot conditions the plants race to see which one can bolt first (bolting is the term used for “running to seed”). More modern varieties are less prone to bolting in hot weather providing they are kept well watered.
It is best to sow lettuce where they are to grow as transplanting can cause a check in growth or cause the plant to be more likely to bolt. Lettuce seeds should be sown in rows 1.5 cm (½¨) deep and about 30 cm (1’) apart, the rows should be short and seed sown thinly. Germination takes between 4 to 12 days and you should thin the plants out once the first pair of true leaves have formed. Depending on the variety the spacing between the plants should be 23 – 30 cm (9 – 12”).
If you must transplant, gently lever the plants out of the ground with a spatula, when the first true leaves have formed. Handled the plants gently by the leaves using your thumb and finger. Place carefully into prepared holes and firm the ground down and water well to ensure that the roots are in contact with the soil. Care should be taken not to transplant with the leaves to high off the ground as this will cause the lettuce not to heart. Likewise planting too low will give rise to mould infections.
For autumn harvesting choose either a cos or cabbage variety bred for autumn harvesting. Again sow the seeds in short rows where the lettuces are to grow, this time in succession from mid-summer to late summer. Once the plants are 5 cm (2“) thin out to leave 23 cm (9”) between the plants. The first sowing should be ready for harvesting in early autumn and the last in late autumn. Now the later sowings may be so slow to grow that they are not ready by early winter, however, if you protect them with cloches or polytunnels they will have a good chance of surviving the winter and will be ready by early spring
For successful winter lettuce you need to be able to provide a temperature of at least 15°C (60°F), in the UK this can only really be done in a well-constructed greenhouse, that is heated throughout the winter. Now unless you have other crops or plants that need this heating the cost of heating the greenhouse for the lettuce makes them very expensive.
If you do want to grow winter lettuce choose a cabbage variety that was bred for winter harvesting. This time sow the seeds in trays filled with good quality compost from early to mid autumn. To ensure germination the temperature should be maintained between 10 and 15°C. Once the first true pair of leaves have formed gently lift the seedlings using a spatula and plant into boxes 23 cm apart. It is important that the temperature is maintained, and that the humidity is also controlled by watering and ventilation.
Growing spring lettuce outdoors unprotected is really only achievable in areas where the winters are mild, and you choose a hardy type. For spring lettuce the ground must be open and sunny and ideally well manure for a previous crop. Sow the seeds in a seedbed in late summer planting out in late autumn. Again the rows should be 30 cm (1’) apart with 23cm (9”) between the plants. Just before the winter sets in give the rows one last hoe and then leave alone until early spring when growth restarts.
To be more successful with spring lettuce you are better off providing some protection over winter, this should be in the form of barn cloches. Follow the instructions above. Once early spring arrives and growth restarts remove the cloches a few at a time. The lettuce plants that are uncovered first are the first to be harvested and this should start in mid-spring.