When To Sow: February-March (under protection); March-August (direct seed) Harvest: June-October
Germination: 4-10 days Full Sun
Lettuce is a cool season crop that prefers a rich, well-drained soil and a pH above 6.5. It germinates best at temperatures from 4-16°C (40-60°F). Germination rates decline above 20°C (68°F).
Choose a location in full sun that has been well-manured (unless sowing in late spring/early summer when partial shade will help keep the plants cool).
Sow at a seed depth of 6 to 12mm (¼ to ½”) in short rows about 30cm (12”) apart. Cover lightly, as the seeds need light to germinate (7-14 days). Thin to a spacing of 15 to 20cm (6-8”) once the seedlings are 2cm (1”) tall. For a continual harvest, make successional sowings every two weeks from spring to mid-summer.
Although most lettuce prefers growing temperatures from 16-18°C (60-65°F), Salad Bowl lettuce is slow to bolt, so there is a longer window of opportunity for both sowing and harvesting.
Keep lettuce plants consistently moist (but not water logged), particularly when the plants are around 2 weeks away from harvesting. Dry soil at this point will cause the plants to bolt, turning the leaves bitter. Applying mulch (grass clippings, straw, leaves, etc.) will help both to suppress weeds and keep the soil moist and cool.
The tastiest lettuce comes from rapid growth, but since lettuce has very shallow roots, it does best with a side dressing of compost a week or so after seedlings appear. Applying compost tea every few weeks will also help to give it its best flavour.
Harvest as soon as they are big enough for the salad bowl. In fact, the earlier the harvest, the more tender the crop. Make sure to harvest before the central stem begins to form. Once this happens the lettuce is going to seed and the leaves will become bitter. Alternatively, pick individual leaves throughout the plant’s growth for a continual supply.