Botanical Name: Latuca sativa
Plant Type: Hardy Annual
Lettuce is no longer just lettuce. Thanks to pioneers like Joy Larkcom, we are becoming used to a huge diversity in the flavours, textures, and colours of lettuce, where lettuce is now used to colour the garden, and not just the salad bowl. Perfect for pots, window boxes and garden beds, lettuce will grow just about anywhere with full sun in winter and spring, and a little shade during hot, dry summers. Lettuce is a member of the milk thistle family producing a milky sap that can make the leaves taste bitter, especially when they are about to bolt up to seed. By selecting the right varieties for the right season, and with regularly watering, this problem can be eliminated. Grow different varieties to boost biodiversity, confuse pests, and for the best-looking salads
A regular addition to our modern diet, cultivated lettuce is derived from wild lettuce, Lactuca serriola,an annual plant related to milk thistle with bitter milky white sap. Varieties grown today have been selected due to their delayed production of bitterness, which leads to a variety of colours, flavours and forms. Originally from the old world, cultivated lettuce dates back to the Egyptians, who selected varieties that were slow to bolt (run to seed) which delays the bitter flavour, and extends the harvest period.
As with other vegetables, numerous varieties of lettuce have been developed through selection over many generations, and today, it is possible to identify distinctive types based on their appearance.
- Crisphead or cabbage types have very compact heads, composed of very light green leaves, and are the familiar long-storage supermarket types.
- Butterheadtypes also have very compact heads, differing mainly from crispheads in leaf texture, by being softer and more supple. They exhibit fast growth and are highly favoured in Europe.
- Costypes derive from the Greek island of Cos, and are identified by a far more open head, which produces elongated, heavily ribbed leaves.
- Loose leaf or cutting types have a very open structure without heads and are notable for a diverse range of leaf colours and a prolonged season.
Grow as many different varieties as possible to experience the range of leaf shapes, colours, textures and subtlety of flavours across this immense range of heirlooms.
Lettuce is a hardy plant that in temperate areas without severe frosts can be grown year around. Plants can be established through direct sowing or transplantation. Sow successively to extend your season and harvest.
Sun: Full Sun – Part Shade
Water: 3 Drip
Soil: For best results, lettuce prefers well-drained soil that is slightly acidic to slightly alkaline. Gardeners with very heavy, clay type soils should consider improving the structure through the addition of gypsum and sand and by hilling up beds to improve drainage.
Lettuce enjoys manure rich in nitrogen, and has a great need for potassium, so adding potash to beds is prudent.
Growing from Seed
Sow: sow direct into well prepared soil in rows
Ease of Germination: Easy
Germination Temperature: 4-26°C (note: seed will not germinate above 30°C)
Germination Time: 2-14 Days
Spacing: 20-30cm apart
Harvest: 50-80 days
Seeds will germinate over a wide temperature range, but are sensitive to high temperatures and moisture stress, so establishing crops during the hotter part of the year is best done by transplanting. Varieties that don’t enjoy the heat can be grown in partial shade during the summer to alleviate the problem.
Most varieties can be transplanted at a spacing of about 30 cm, with the larger varieties at 40 cm. Mini varieties, such as Tom Thumb, can be spaced at 10 cm to 15 cm, or can be conveniently used to fill in the gaps between plants of larger varieties.
Lettuce needs some care during transplanting, for excessive stress can induce them to run up to seed prematurely. Always transplant in the cool morning, preferably on mild overcast days in the warmer weather.
Lettuce has comparatively shallow roots, resulting in a number of consequences for gardeners. For soil preparation, avoid placing fertilizers or manure too deep and out of reach of the plants. The shallow root system is easily damaged during weeding.
Maintenance and Additional Care
The plants can rapidly stress if moisture levels drop, in which case the growth will be checked, and they will tend to develop bitter flavours.
Mulching to control weeds and retain soil moisture is strongly recommended. Drippers are preferable to spray watering because they discourage the growth of a number of rots and downy mildew.
Good companions: Beans, beetroot, capsicum, carrot, cherry, chervil, chilli, cucumber, dill, marjoram, onion, passionfruit, peas, radish, and strawberry.
Bad companions: Broccoli, Brussels sprouts, cabbage, cauliflower, celery, kale, and parsley.
Beneficial flowers: Achillea, coreopsis, French marigold, and zinnia.
Pests and diseases
A number of diseases and pests can severely affect lettuce. Young plants can be devastated by slugs and snails, but this can be alleviated using snail baits. An organic method of control is to set up shallow trays containing beer, which attracts the slugs, which then become intoxicated and drown. There are no arguments among slugs about the brands of beer because all seem to work!
Both young and established plants can die from the damping-off fungus, so setting up well-drained beds and avoiding over-watering is necessary to reduce losses. Similarly, lettuce can be affected by the fungus Sclerotinia. If it appears, it is best to move the bed for a few seasons.
If present in large numbers, insect pests, such as aphids and leafhoppers, can severely debilitate lettuce and also introduce several diseases. Both are easily controlled with organic insecticides. Aphids transmit the virus known as necrotic yellows, which results in stunted plants with distorted green and yellow blotches, highlighted by dirty brown veins. Infected plants should be destroyed, and prevention can be achieved through spraying for aphids and destroying milk thistles, which are an intermediate host for the virus.
Planting edible flowers with your lettuces attracts predators such as ladybugs and lacewings that will control pest numbers.
Lettuce grows well in pots and containers. Select loose leaf varieties to maximize your space and harvest. Always use a premium potting mix when growing in containers. Water morning and night to maintain adequate soil moisture and liquid feed regularly for quick growth and to avoid bitterness.
To avoid bitterness in varieties producing heads, always harvest before the
central portion of the head becomes conical (in preparation for running up to seed).
Leaf lettuce varieties can be harvested leaf by leaf, almost to the ground, and they then resprout or are left to produce heads. They are the preferred choice of cooks.
Cos lettuce varieties are tolerant of extremes of temperatures and have tall upright stems that do particularly well throughout winter. These can be harvested from outer leaves first, or as an entire head.
Head lettuce, like those typically found in the supermarket, are crisp head types with little flavour but longer storage.
Seed Longevity: 5 years
Isolation Distance: 3m with a tall barrier of other vegetables in-between or 6m in an open situation.
How to Save Seed: When left too long in the garden, lettuce regularly runs to seed (grows tall, flowers, and sets seed). Many gardeners are happy to leave these to self-sow and grow where they fall, but if you hope to save seed, you will need to harvest the entire plant after flowering, when the flowers start to become fluffy.
Be quick, as these will readily dislodge. Hang the entire plant upside down over a large bucket or tub or place in a large paper bag to catch the seed. Once dry, rub the seed heads to collect as much seed as possible. The seed will separate from the chaff and can be sieved to produce clean seed, ready for saving. Store in a seed saving envelope in a dry, cool, dark place.
Tips and Tricks for Success
- climate plays an important role in variety selection, especially as lettuce is generally considered to be a cool-climate vegetable. In warm climates, select slow-growing crisp head varieties that show bolt resistance to lengthen your harvest, while in cool climates select fast-growing varieties.
- use shade, especially in warmer areas and seasons, to help extend the life of your lettuce.