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Organic Gardening:

How to grow organic Lettuce

by Frann Leach

Crisphead lettuce

Lettuce

Lactuca sativa

Family: Compositae (Group 4)

There are 4 types of lettuce: butterhead, crisphead, cos and loose-leaf (salad bowl):

Butterhead: the traditional floppy-leaved lettuce. Mainly grown in summer but some hardy cultivars are available, suitable for winter cultivation in unheated greenhouses.

Crisphead: usually larger than butterheads, with crisp, wrinkled leaves. Includes Iceberg types (with large white hearts, usually sold with all outer leaves removed) and Webbs Wonderful types. Mainly grown in summer, but some cultivars are suitable for winter cultivation in unheated greenhouses.

Cos: upright, thick-leaved, with a fairly loose heart. Slower to develop than other lettuces, they grow better in cool weather and are quite hardy. Some are even suitable for overwintering outdoors.

Loose leaf (salad bowl): forming a loose rosette of leaves with no heart. Leaves can be picked individually or heads cut off across the stem and left to resprout. Slow to bolt; heat and cold tolerant. Can be grown outside most of the year and in unheated tunnels or frames in winter.

By careful selection of varieties and use of heated facilities, it is possible to produce fresh lettuce for at least 11 months of the year, though why one would want to, with the variety of other salad greens available, is beyond me.

Summer lettuce matures in about 12 weeks, butterheads first, followed by crispheads, and then cos. Butterheads will only stand for a few days before they start to bolt, crispheads about a week longer, while cos stand reasonably well so long as the weather is cool. For this reason, many gardeners make successive sowings of small quantities every 2 weeks throughout the season, or you may prefer to rely on the loose leaf types, which can usually be picked over several months.

Recommended cultivars

Early sowings under cover:

Hilde¹, Jaguar ², Little Gem³, Winter Density³

Main outdoor sowings:

All the Year Round¹, Avondefiance¹, Windermere², Avoncrisp², Jaguar², Bubbles³, Lobjoit's Green³, Winter Density³, Lollo Rossa⁴, Lolla Bionda⁴, Frisby⁴, Cocarde (oak leaf)⁴, Samantha (oak leaf)⁴

Protected winter crop:

Kwiek¹, Marmer², Marvel of Four seasons⁴

Outdoor overwintering:

Valdor¹, Winter Density³

Autumn sowing for early crop in heated greenhouse:

Kloek¹, Kordaat¹

¹ Butterhead

² Crisphead

³ Cos/semi-cos

⁴ Loose leaf

Site/soil

Lettuces need an open site and light, fertile, moisture retaining soil. They do not do well in poor soil or soil which dries out in hot weather. Ideal pH is 6.8-7.5.

Dig over the ground the previous autumn and apply plenty of compost or manure. A base dressing of 1oz fish, blood and bone and 1oz rock potash per square yard can be applied 10 days before sowing or planting. Liquid feeds of seaweed fertiliser may also be applied during the growing season if growth seems slow.

The smaller lettuce cultivars and lettuce grown as cut and come again seedlings can be used for intercropping. Loose leaf types also make attractive edging for vegetable or flower beds, especially the oakleaf varieties.

Sow 1-2cm (½-¾") deep either in situ (which is best in hot weather), in seed trays or modules. In cool weather lettuce can also be sown in seedbeds and transplanted. Thin as soon as possible after germination to the correct spacing as follows: small cultivars (e.g. Little Gem) 15-20cm (6-8") each way, standard butterhead: about 28cm (11") each way, crispheads 30x42cm (12"x15") or 42cm (15") each way for larger heads, cos and loose leaf: 40cm (14") each way.

Water regularly in dry weather at a rate of 4 gallons per sq yard per week. If water is in short supply concentrate on the period 7-10 days before maturity.

High temperature dormancy

Lettuce seed often fails to germinate at soil temperatures above 77ª F (25ª C), especially during the first few hours after sowing. To overcome this:

Water after sowing to reduce soil temperature
Use a white reflector to cover the seedbed until the following day, e.g. newspaper
Sow between 2 and 4pm, when the soil is starting to cool down

Alternatively, seed can be sown in trays or modules kept somewhere cool to germinate, or jelly sown.

Cultivation table for a year-round supply of lettuce

Cultivar

Sowing notes

Harvest

Kloek¹

Sept-Oct in situ in heated greenhouse

Jan-March

Marmer²

Oct in cold greenhouse/frame

April

Winter Density³

end Aug-early Sept, thin to 3", liquid feed in March

May-June

Little Gem³

mid-Feb under cloches. Remove covers 3 weeks before maturity or in hot weather

late May-early June

Jaguar²

mid-Feb under cover, transplant into divided tray at 7 days, planted out mid-April

end May to end June

All the Year Round¹, Avoncrisp²

successively late March-early July supply cloches in Autumn

June-Oct

Lolla Rossa⁴,
Lolla Bionda⁴

April-May

July-Oct

Avondefiance¹, Avoncrisp²

early August, cloche in Sept

Nov-Dec

¹ Butterhead

² Crisphead

³ Cos/semi-cos

⁴ Loose leaf

Special commercial cultivation method for early spring lettuce

Preparation:

Lettuce will be grown in polytunnels or cold frames, which should be prepared in advance of planting. Polytunnels are left well-ventilated, cold frames left open to obtain full benefit of rain.

Apply lime as necessary to adjust pH to 6.8 (6.0 for peat soils).

Apply a base fertiliser dressing of 2oz bone meal and 4oz rock phosphate* per square yard (or 3oz/square yard Growmore 100% organic).

*Apply rock phosphate once every 4 years only.

Sow in soil blocks 4cm (1½") square in polytunnel or cold frame. Seed can also be sown broadcast and pricked out to 5cm each way (2"x2") before finally transplanting, or 150 seeds to a seed tray, transplanted 40 per tray or into soil blocks.

Prior to planting, cover frames to allow the soil surface to dry out. Prepare soil to a fine tilth. It is important that the soil is not walked on subsequently. Plant out in January 22cm each way (8"x8") or 22cm by 13cm (8"x5"). Plants are planted shallowly, not very firmly. Soil blocks are merely placed into a depression made by a planting machine so that two thirds of the block is above the soil surface, which keeps leaves off the soil, aiding against botrytis and keeping the leaves clean. This should avoid the need to trim plants prior to packing for market or consumption, maximising yield.

Cover frames, but give ventilation in warm spells and towards maturity. A liquid feed of comfrey liquid in March is useful if the soil is not over-rich.

Watering should not be necessary on heavy soils, but may be needed on light soils. Do not water in bright sunshine.

Test hearts gently with the back of the hand and cut those which are ready, handling with care. Best time is in the cooler part of the early morning.

If you're interested in healthy food, you may also be interested in our sister site, The Health Site, Your Online Health Channel.

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