There are three types of lettuce, the cabbage, cos and loose leaf. Choice may be determined by personal taste, some people liking the crispness of the cos, while others prefer the softness of the cabbage and loosetleaf types. Soil must be rich and well prepared to encourage quick growth. Manure or compost should be worked in prior to planting at the rate of 1 cwt. to 10 sq. yd. Just prior to seed sowing, the soil should be dressed with a mixture of 5 parts of superphosphate, 2 parts of sulphate of ammonia, and 2 parts of sulphate of potash at the rate of 3 oz. per square yard.
Seed should be sown thinly in drills 1 in. deep and 1 ft. apart for the bigger varieties or 9 in. for small kinds such as Tom Thumb. Small successional sowings should be made about once every three weeks from the end of March to the middle of August. Earlier supplies can be obtained by sowing in February in a greenhouse or in a frame or cloche on a hotbed. Sow broadcast in shallow boxes; prick seedlings out 2 in. apart each way into similar boxes as soon as they can be handled. Then the plants can be gradually accustomed to outdoor conditions in readiness for planting out in mid-April. Winter supplies can be obtained by sowing in a frame during the first week in October and transplanting the seedlings to another frame or greenhouse when they can be handled. It is very important with all lettuces grown under glass to plant shallowly. The lowest leaves must be above soil level or damping off may occur.
Thinning out of seedlings raised in the open should be done as soon as they have two or three true leaves each. Leave the plants standing 6-9 in. apart in the rows. The thinnings can be replanted in another bed.
An occasional dusting of soot (1 oz. to 4 ft.) or of nitrate of soda, Nitro-chalk, or sulphate of ammonia (1 oz. to 12 ft.) may .be given between the rows. Discontinue application of fertilizers as hearts form.
Reliable kinds are — Cabbage type: Continuity, All the Year Round, Trocadero, Webb’s Wonderful, and Tom Thumb; Cos type: Little Gem and Paris White. For autumn and winter use, Arctic King and Imperial (cabbage) and Winter Density (cos) are reliable. For frame or greenhouse culture the cabbage varieties May Queen, Delta and Cheshunt Early Giant are recommended. Salad Bowl is a good loosetleaf (heartless) variety. Buttercrunch is intermediate and semi-hearted.
Aphids on leaf and root, cutworms, and slugs are the pests most to be feared. Grey mould, mildew and damping off, the worst fungal diseases.
Sowing to harvest time: 10 to 14 weeks.
Yield: 10 to 30 heads, depending on the variety, to a 3 m (10 ft) row.
Ideal growing conditions: Cool temperate.
Position: Open and sunny, but in summer lettuces are better in partial shade.
Soil: Well-drained and rich in humus.
There are two distinct types of lettuce: cabbage, and cos. The cabbage kinds can in turn be subdivided into butterheads, with soft floppy leaves, and crisp hearts, which have crisper leaves than the butterheads and are more resistant to summer heat and less liable to run to seed. Cos lettuces are upright and have crisp self-folding leaves. The cos type of lettuce does not run readily to seed and its leaves remain much cleaner in wet weather. There are several dwarf varieties of lettuce which are a good choice for growing in tubs and window boxes. Such small lettuces generally provide enough leaves for two people for one meal.
Sowing and planting
The soil for lettuces should be enriched if necessary with some well-rotted compost. About two weeks before sowing or planting out, the soil should be given a top dressing of vegetable fertilizer at the rate of 70gm per sq m (2oz per sq yd). For a summer crop, sow outdoors from the end of early spring to late midsummer to produce lettuces from early summer until the end of mid-autumn. For an early winter crop, sow a forcing variety in late summer and cover with cloches from early autumn to provide lettuces in late autumn and early winter. Forcing varieties can also be sown in the greenhouse from late summer to mid-autumn to provide lettuces from late autumn to mid-spring. For a spring crop outdoors, sow a hardy winter variety at the end of late summer or in early autumn and harvest in late spring. For lettuces in mid-spring, sow a forcing variety at the beginning of mid-autumn and cover with cloches.
Pests and diseases
Aphids, birds, millepedes, root aphids, slugs and botrytis (grey mould).
Lift from the garden in the early morning while the leaves are crisp and fresh.