HOW TO GROW LETTUCE IN THE UK
By David Marks
Lettuce forms the basis of almost all salads with the gardening books and online articles making out that they are relatively easy to grow, one of the simpler vegetables. In truth there are several rules you need to follow, none of them complicated but together essential, that must be followed for a good crop of lettuce.We aim to simplify the process but at the same time clearly identify the key essential steps to grow perfect lettuce in plain and simple language.
There are several different types of lettuce and it’s a matter of personal preference which you prefer. All are capable of being grown in the UK but we have yet to see iceberg types of lettuce being grown successfully in the UK by amateur gardeners. This article restricts itself to the following types of lettuce for the amateur gardener, Cos (sometimes called Romaine), butterhead and loose leaf lettuces. For more information on the different types of lettuce click here.
CALENDAR FOR GROWING LETTUCE IN THE
- Sow seed in pots indoors – The last week of February
- Sow seeds under cloches – The second week of March
- Sow seed outside – The last week of March
- Plant out indoor sown lettuce – The third week of March
- Begin to harvest The fourth week of July
The soil needs to water retentive above all because lettuce require a constant supply of water if they are to grow evenly and avoid bolting. A fairly neutral soil is good for lettuce and they prefer a good supply of nutrients. A sprinkling of blood, fish and bone at the rate of a good handful per square metre will suit lettuces well – do this a couple of weeks before seed is sown / seedling are planted.
At the start of the growing season, up to mid-June, lettuce will do best in full sun. Past this, and up to the end of August, they would prefer some partial shade because lettuces prefer cool conditions. These conditions are not always easy to achieve however and lettuce are in general very tolerant of both sun and partial shade at any time of the year.
Some lettuce seeds are sold as “split-pill” seeds and this often confuses. A split-pill seed is one where the outer casing is slightly broken open to allow quicker and easier germination. It does not affect the “when” and “how to” sow as far as seeds are concerned.We can find no independent data to indicate that “split-pill” seeds are any better at germination compared to standard seeds.
The germination temperature for lettuce seeds is anything in the range of 2°C / 35°F, the optimum temperature range is 15°C / 59°F to 19°C / 67°F. Although lettuce seed have an amazing ability to germinate at low temperatures, the lower the temperature outside of the optimum range. the slower and more erratic the germination will be. Above 20°C / 69°F the germination rate of lettuce seed will also deteriorate.
When considering the germination temperature of lettuce seed, it is only important for the first couple of days after the seeds have been sown. The minute the seed sprouts (the little initial sprout is called the radicle) the temperature, as far as germination is concerned, is unimportant. So, this means that if you sow lettuce seeds in pots and keep them at 15°C / 59°F to 19°C / 67°F for three days they can then be moved to cooler or warmer conditions depending on your situation.
It’s very important to prepare the soil before sowing seed or planting seedlings. The soil should be well dug and the surface should be raked over to a fine tilth and be reasonably even. Only if the soil surface is even and a fine tilth will you be able to sow the seeds at the correct depth.
The individual sowing and planting methods described below can be used for sowing lettuce seeds in spring and harvesting from late spring onwards. If you are sowing in autumn for an early winter crop (common with several butterhead varieties) then sow only directly in the soil outside.
SOWING LETTUCE SEED DIRECTLY IN THE SOIL OUTSIDE
This is the simplest method and will have a very good success rate if the soil is prepared as described above. If slug and snail damage is a known problem in your garden / allotment then you might be better off sowing the seed in pots and only transplanting to their final position when they are large enough to avoid serious damage by slugs and snails. Don’t sow all the seeds at the same time, sow some every week or so to ensure a good supply of lettuces over a long period of time. Start sowing in seed in and continue to sow small amounts of seeds weekly or fortnightly over the next 10 weeks.
Sowing seed directly in the soil during July and August will result in poor seed germination because the soil temperature is likely to be too high. However sowing can resume for a couple of weeks in September when the weather is cooler.
Draw a shallow line in the soil with a pencil / dibber or similar to a depth of about 1.5cm / ½in. Lightly sprinkle the seed into the soil line at the rate of about 1 seed per centimetre. With such fine seed it’s difficult to sow at the correct rate but it’s not crucial. Cover the seeds gently with soil and then water in using a watering can with a fine rose.
SOWING LETTUCE DIRECTLY IN THE SOIL UNDER CLOCHES
For earlier crops compared to the sowing method above the seeds can sown with cloche protection. Place the cloches over the soil for a couple of weeks before the first sowing in. The method of sowing the seed is exactly as described above. Remove the cloches when the weather warms up, normally in about five weeks time.
SOWING LETTUCE SEED IN POTS INDOORS
The aim behind this method of sowing lettuce seeds is to grow the earliest crop of lettuces possible. The seed is sown in pots indoors, then transferred outside with cloche protection and then the cloches are removed. The process can omit the cloche stage if there is lots of space indoors / in a greenhouse.
In fill pots or seed modules nearly to the top with general purpose multi-compost. Sow three lettuce seeds per pot and cover lightly with more compost. Water if the compost is dry and then place the pots in a temperature of 15°C / 59°F to 19°C / 67°F. the seedlings should appear after five days or so and the pots can then be moved to somewhere cool but frost free. Keep the seedlings growing on in a light position but not in direct sunlight.
Around plant outside in their final positions under cloches (a couple of weeks later if no cloches). Remove the cloches in three weeks time.
WHY GROW YOUR OWN LETTUCE?
Finding out exactly how commercial lettuce is produced can prove very difficult, the producers seem unwilling to publicise exactly how that bag of supermarket mixed salad, for example, has been treated before it reaches you. The following seems clear:
- It has been sprayed multiple times with various chemicals during the growing process.
- In all likelihood it has been packed in a nitrogen / carbon dioxide enhanced atmosphere. Ever wondered why bagged lettuce leaves are sold in pumped up bags? It’s because the “air” in the bag is not real air but is modified to prevent the contents discolouring as it ages. This enables the supermarkets to sell old lettuce which just looks fresh.
- Unless the pack says differently, and not many do, the lettuce in the bag will have been washed in a chlorine solution far more concentrated than the water in a public swimming pool and they don’t rinse the chlorine off before it reaches you!
- The whole process ensures that bagged lettuce is several days old before you eat it. It may look good in the bag but much of the nutrient value and taste has disappeared long before you eat it.
Here are a couple of articles on bagged lettuce production; Countryfile, Healthy Food. They all come to the same conclusion, eating chlorine is not good for you and eating four or more day old salad is also a waste of time whatever has been pumped into the bag to preserve the contents well after its natural life.