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How to Grow Lettuce: A very simple guide

By chadchaffin | Gardening

Dec 17

This familiar crop has been the main ingredient of salads for centuries. But over the years the humble lettuce has changed, offering gardeners a wider choice of colours and textures, creating the perfect salad accompaniment to any meal.

When to sow

Early sowings can be made from February to April for summer lettuce; these are sown into pots and pricked out into trays and grown on under glass until large enough for transplanting out on the plot after being hardened off in a cold frame. From April to August sowings can be made either direct into the plot or sown in pots and then transplanted to the plot. From early September through to mid October winter lettuces can be sown direct under cloches or raised in modules and transplanted out.
These will grow outside all winter and will mature from March-May the following year depending on the harshness of the winter. Gardeners with a cold greenhouse or polytunnel can grow lettuces throughout the winter.These are sown from September to November and will mature from January-April depending on how cool the greenhouse gets. When growing this type of lettuce try to keep the temperature under glass just above freezing for the best results. It is also important to give the greenhouse some ventilation on warmer dry days of winter to help avoid any grey mould problems.

Sowing the seed

Many gardeners sow their lettuces direct into the vegetable plot in shallow drills approximately 1cm (½in) deep.Then once they have germinated and the seedlings are large enough to handle they are thinned out or even transplanted into other rows. I find this method okay for early spring sowings, but as soon as the weather gets warmer the results can often be quite poor. Over the past 20 years I have rarely sown any lettuce direct outdoors, changing instead to sowing little and often all through the year in pots, often only growing 12 plants per variety. Sow a few seeds every two weeks under glass into flowerpots filled with moist seed-sowing compost, and then lightly cover the seeds with vermiculite.

Lettuces germinate better when sown cooler, so there is no need for a heated propagator, the pots can be stood on the greenhouse staging where the temperature will be between 10-15ºC (50-59ºF) and they will start germinating after seven to 10 days. When sowing lettuce during the summer and with the days getting hotter, gardeners often find it difficult to get lettuces to germinate, especially if there are several days where the temperature exceeds 21ºC (70ºF), as high temperatures will inhibit germination. To overcome this problem place the seed packets in the fridge the night before they are to be sown. This overnight pre-chilling seems to be enough to help the seeds cool down and then, once sown, they will germinate very well during these hot spells.

Growing on

Once the seedlings have germinated in the pots, prick them out (transplant) into cell trays (modules) and grow them on until they are ready for planting out. Before planting out, however, early sowings should be moved into a cold frame for a couple of weeks to gradually harden off. Lettuces will grow in any good soil that has been winter dug and enriched with organic matter. Before sowing or planting, give the soil a dressing of growmore fertiliser added at a rate of 60g per sqare metre (2oz per square yard), lightly raked into the surface of the soil. Seedlings sown direct should be thinned before the plants become too large to 15-30cm (6-12in) apart, depending on the size of the variety being grown.
The best time to thin out and transplant seedlings is in the evening when the temperature is cooler. After thinning, plants should be watered along the row straight away to help settle them back into their positions and recover overnight.

If using the thinnings as transplants to get another slightly later maturing row, this is best done straight away, removing a few plants at a time, planting before they wilt and thoroughly watering them afterwards so the roots are cool and wet. This will help them to recover quickly. Over the next week, water these transplants as necessary each evening to keep them turgid. Plants raised under glass and transplanted from modules get away a lot quicker with no root disturbance and producing a far superior lettuce.
Plant out each lettuce with a trowel at the required distance, water them in straightaway and you will see them grow away almost immediately.Throughout the growing season, fill up vacant spaces with later sown modular raised plants to keep the plot full and productive.

Early in the year, if the weather is changeable or very wet, windy and there is a risk of hail, cover the plants with a cloche made from Enviromesh or fleece for added protection. As plants grow, keep the weeds down by hoeing at regular intervals.
Two weeks after transplanting the plants are usually well established and watering can be stopped unless the weather is very hot and they begin to wilt; watering larger plants too much can encourage botrytis (grey mould) and mildew diseases.

Pests and Diseases

Occasionally, young seedlings or freshly planted out modules can be attacked by birds pecking the leaves; these can easily be deterred by covering the rows with some netting. Lettuces also make a tasty meal for slugs and snails, so it is best to protect these with whichever slug control you prefer to use to help combat this troublesome pest.
Lettuce root aphid and leaf aphid (greenfly) can be controlled by using a suitable insecticide, but always check the label before spraying to see how long after treatment you can safely harvest the crop.

Alternatively, grow one of the lettuce aphid resistant varieties. Occasionally, downy mildew disease can be a problem, but these days this is less so since the introduction of mildew resistant varieties. Grey mould is normally only a problem during very cool, damp weather conditions or on lettuces that are grown under glass through the winter with insufficient air circulation. If this is seen, plants should be destroyed to avoid the disease spreading to other plants.

Harvesting

Always try to cut lettuces one to two hours before you need them, wash immediately and place the leaves in the fridge to crisp up for that perfect salad. When preparing, either tear away the leaves
from the stem or cut using a plastic knife to help stop the leaves browning at the base while in the fridge for a few days.
When choosing a lettuce that produces a firm heart, always feel along the row and cut the one that feels the fullest; this way you will always be using the most mature lettuce first and helping to avoid wastage and stopping older lettuces running to seed. When selecting a loose leaf variety, this is easier because you can either cut the whole lettuce or pick the required amount of leaves from the plant needed to garnish your meal.

Pictures: Andrew Tokely and Kings Seeds

Credit: Kitchen Garden Magazine

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