With very careful planning, growing your own lettuce can give you a crop throughout the year, they are among the most popular of the salad vegetables and are easily grown.
There are many types of lettuce but the three main ones are; cabbage varieties, which because they are hearted look like cabbages hence the name, The Cos varieties which are taller and crisper and then the frizzy-headed loose leaf American varieties.
The cabbage varieties can be sub-divided into butterheads and crispheads. Butterhead varieties have hearts that are butter-coloured and are tender. While the crispheads have much crisper hearts that tend to be white in colour. The taller Cos varieties are also blanched with many varieties having leaves that fold in on themselves to self blanch. The American varieties do not have hearts as such and are picked as single leaves as and when required.
Since the 1960’s there have been many developments in producing varieties of lettuce that will grow at different times of the year, so it is now possible with care to grow them all year round. Furthermore, there are dwarf varieties that can be grown in single pots on a sunny windowsill. It is therefore very important that you select the correct variety if you intend to grow outside of the “normal” growing season.
Although they prefer a rich light soil that is well-drained, they will grow well on most garden soils. In the autumn an application of farmyard manure, green manure or rich compost, at the rate of 6kg per sq m (13 lb per sq yd) is an absolute must, as this increases the humus content of the soil and helps to retain water, which is very important as lettuces are 90% water. They also need a soil pH of about 7.5 so a soil test before sowing is a good idea and if necessary apply lime to adjust the pH. If the soil is poor or ill-prepared then they will produce floppy leaves and will not heart-up.
Providing the soil has been properly prepared then lettuces are a good vegetable to intercrop between rows of other vegetables that take longer to grow, an example would be between tall varieties of peas.
Planning your crop
As already stated it is possible to grow them throughout the year, this is done by successional sowings different varieties, i.e. sowing a small number of seeds at fortnightly (every two weeks) intervals. It will also be necessary to have the ability to maintain a temperature of 15°C (60°F) during the winter. Lettuce is classified by the season it is harvested, and not by the season of sowing, so pick your variety according to your needs at harvest time. The classification is really simple, basically the four seasons, summer, autumn, winter and spring. I have given more details here on growing throughout the year.
I can't say this enough the soil must be well prepared and have plenty of humus to retain water. Lettuces also need warmth, moisture and a weed-free environment, they also need protection for garden pests. Do not try to force the growth by overwatering. It is a good idea to place a mulch of well-rotted organic matter to help keep moisture in the soil, or placing strips of black plastic near the plants will do the same thing especially if put down after it has rained. It is important to keep weeds down so regular hoeing between rows is needed to stop any weeds from taking hold.
If you are growing a cos variety that is not self-blanching it may be that you would like to blanch the plants to increase their crispness. If this is the case then about two weeks before you are ready to harvest place a rubber band around the thickest part of the plant, then a week later put another one 15cm (6¨) further up.
Once they are ready for harvesting they need to be cut as the quality will very quickly fall away. If the heart starts to form a point and push upwards the plant is beginning to bolt (go to seed). A lettuce is ready to harvest when the heart feels firm, test this by pressing with the back of your hand and not your fingers to avoid bruising.
Cut the lettuce with a sharp knife just above the lowest leaves, or pull it out by the roots. If you are going to store the lettuce it is best to pull the whole plant and leave the roots on, cover the roots in a plastic bag and chill it will then keep fresh for about a week.
The American varieties are harvested in a different manner by pulling off individual leaves from the outside of the plant. These leaves should be firm but still young and tender.