Michael Michaud on growing and harvesting lettuce
PUBLISHED: 16:54 26 March 2014 | UPDATED: 16:56 26 March 2014
At their best lettuces are refreshingly crisp and slightly sweet, and when matched with garden-fresh cucumbers and tomatoes, they make a summer salad that is as close to heaven on earth that a gardener can get
Lettuces come in all shades of green - from pale olive to bright lime and with a dazzling variety of leaf types from smooth-edged to frilly. The more exotic looking ones have leaves overlaid with red - ranging from small freckles dotting the leaves to large swaths covering almost the whole surface, making them suitable for inclusion in an ornamental border.
Though colour adds visual appeal and distinguishes one variety from another, it is not the most important feature of lettuces. The plant is defined more by its growth habit and the physical form it takes at maturity. On this basis, lettuces fall into distinct types, which affect both eating quality and the management of the crop.
These have leaves packed close together to form a head in the centre of the plant. They divide into the following;
Elongated, upright leaves form compact, torpedo-shaped heads. The smaller-framed varieties produce firm, dense heads, while the heads of the taller varieties tend to be looser and more open. The texture is crisp and crunchy, and the plants – especially the smaller ones – mature quite quickly.
Examples: ‘Little Gem’ and ‘Lobjoit’s Green Cos’
Produce large, firm and roundish heads made of crisp leaves that are blanched in the middle. With their spreading outer leaves removed, they are sometimes sold as ‘icebergs’ in the shops and supermarkets.
Examples: ‘Saladin’ and ‘Lakeland’
Generally refers to varieties that produce smaller, less dense heads compared to the crispheads, though some are non-heading. Popular in France, Batavia have a reputation for their excellent flavour.
Leaves are soft and have an oily mouth feel. The outer leaves are prostrate, while those in the center form a small, loose head. Plants are quite quick to mature.
Examples: ‘Tom Thumb’ and ‘Clarion’
These are quick-growing varieties that don’t form a head. These can be picked as individual leaves when required, or cut as a full lettuce.
Examples: ‘Red Salad Bowl’ and ‘Ashbrook’
Growing and harvesting
Though some varieties can be overwintered in an unheated greenhouse or tunnel, the majority of lettuces have been bred for growing outdoors from spring to autumn. Starting a crop is a cinch (see box) – it’s just a matter of deciding which method to use. You could, for example, produce transplants in module trays filled with a fine-textured commercial compost. Sow some seed in each cell and give the seedlings time to grow and develop – at least four weeks. Once the roots of the plants fill the cells, transplant them either to a well-worked spot in the garden or a large, compost-filled container. If you’re not equipped for transplant production, simply direct sow the seed where the crop will remain until it is harvested, either in the ground or containers.
For lettuces grown in the ground, mix in some pelleted chicken manure to supply the crop with nutrients. In contrast, container plants grown in compost can be given a liquid feed once a week to keep them going until harvest. The plants must be kept moist so that they don’t suffer a check in growth. Be especially careful with those in containers as they dry out quickly on hot, windy days.
Although lettuces are often used in a cut-and-grow-again system for baby leaves, individual plants are traditionally cut once, after they reach full size. It’s easy to tell when to harvest heading lettuces as they form a head, but it is less easy with the loose-leafed types. In principle, cut the plants after they have filled out with leaves, but before they go to seed and start to deteriorate – experience will teach the best practice.
Lettuces are best eaten straight from the garden, before they get a chance to wilt. If you need to store them for any length of time, do the harvesting in the morning, when the temperature is still cool. Then store in a sealed plastic bag in the refrigerator – they should keep fresh for up to a week.
Pests and diseases
Slugs, rabbits and other grazing animals can devastate a crop and must be controlled, particularly early in a crop’s life. Mildew is a fungal disease that becomes a problem when the weather turns cool and moist. Many lettuce varieties have been bred for varying degrees of resistance, so grow one of those to reduce the chances of infection.
Quick tips for starting outdoor lettuces
Distance between plants: In order to reach their full size, lettuces must not be crowded too close together. Space the plants equidistant from each other, preferably in a triangular pattern. Leave about 30cm each way, reducing this distance to about 23 or 24cm for smaller varieties like ‘Little Gem’ and ‘Tom Thumb’.
Sowing depth: 3mm to 6mm
Sowing strategy: Lettuces can be grown in the ground or in compost-filled containers. Start a crop as transplants in module trays, or direct sow where the plants will remain until harvest. Place two or three seeds in each cell (for module trays) or at each ‘post’ (if direct sowing), thinning down to one seedling after germination is complete. Sow every 2 or 3 weeks for a continuous harvest, remembering that the exact timing varies according to the variety grown and time of the year. Avoid temperatures above 25ºC – otherwise thermodormancy will inhibit germination of some varieties.
Sowing date: Sow seeds outdoors from mid-March to late July. For an earlier crop (either started as transplants or grown in containers) begin sowing undercover from mid-February.
About Michael Michaud
Michael and Joy Michaud run Sea Spring Seeds, a Dorset-based company specialising in the production and sale of vegetable seeds and chilli plants. They also breed chillies and have developed several new varieties, including the world’s hottest chilli the Dorset Naga. For more details visit their website seaspringseeds.co.uk.