Lettuce Are A Relatively Varied, Quick Growing And Easy Crop To Grow, Which For Many Of Us Can Be Sown And Harvested 365 Days A Year. Learn How to Grow Lettuce Now.
But before sowing it’s probably best to get to understand a few lettuce basics.
Types of Lettuce
Butterhead are the first type I ever grew commercially. They are normally grown to cut as a hearted lettuce and not as a “cut and come again” type. The growth is generally softer than most other varieties with thinner leaves and a ground-hugging type of growth. Sometimes called roundhead lettuce this perhaps describes them best. They come in all shades of green and when I grew them commercially I found the lighter greens were favoured in the south and darker greens in the north of the country. Why? I’ve no idea.
Cos lettuce have a more upright growth and look a bit like London’s iconic Gherkin … but much smaller of course, they tend to be around 25 cm high. That’s not to say they can’t grow into a heavy lettuce. They can and do.
Lakeland lettuce preceded crisp/iceberg lettuce. They formed a good heavy heart, were crisper than both butterhead and cos lettuce, but not as crisp as modern crisp lettuce. In my opinion they had more flavour than today’s crisp lettuce, but were more prone to mildew.
Crisp/Iceberg lettuce are an advancement on the old fashioned Lakeland type lettuce. They are more compact and have excellent keeping quality.
The above lettuce all form dense hearts if grown correctly. However, in recent years there has been a tendency for amateurs to grow loose-leaf varieties of lettuce. These are sown densely and harvested as leaves rather than hearts. They can be either snipped off with scissors and the plant then discarded, or they can have individual leaves harvested. The latter method allows the plant to continue growing and able to be harvested every few days. This prolongs the season and can result in large weights of lettuce being harvested per unit area.
Loose leaf varieties tend to be grown as mixed varieties with different leaf shapes and colours. The flavour varies very little in most cases but colours can go from pale greens to deep reds. As the lettuce gets older they tend to become more bitter. Some people prefer this and others dislike it.
Lettuce Sowing In-situ
Lettuce can be sown in situ or in plugs/modules/blocks for later transplanting.
When grown in situ the soil needs to be finely cultivated and fertile. Adding a base dressing of general purpose fertiliser, as per manufacturer’s recommendation, before drilling/sowing is generally recommended.
Where large quantities are being grown, seeds can be drilled by tractor mounted machine or a brush drill. But most amateurs find sowing small quantities by hand the ideal method.
Scrape a shallow drill (groove) in the soil. Drizzle a small amount of evenly spaced seed into the drill and rake the soil back over them. The depth of the drill should be about 5–8 mm (quarter an inch) deep. And the seed needs to be spread thinly. A seed every inch is ideal in normal growing conditions.
Once the seeds have germinated thin them to one strong plant every 8–12 inches (20–30 mm).
Leave the same distance between the rows.
Spacing isn’t that critical in garden situations. Roundhead lettuce are about 8 inches in diameter, with cos and crisp about 10 inches in diameter. So if you aim for this sort of spacing they will fill the space and swamp out most weeds. Give them too much space and they will get splashed with mud if it rains heavily.
If plants are spaced too close together they tend to grow smaller … and growers tend to use this fact to determine the head size when growing some crops.
Lettuce Sowing in Modules/Blocks etc.
Lettuce are an ideal crop to start in blocks or modules as they happily transplant.
Commercially we started lettuce as single plants in a peat block (produced by a machine it turns damp peat into a series of individual growing blacks joined like a chocolate bar, and so needs no container as such). Each block was sown with a single seed and this was germinated in the block and then grown on until planting size.
The commercial peat block system demonstrates how flexible lettuce are and how easy it is to grow them. Because germination rates are close to 100% there is no need to sow more than one seed per black. Hence I recommend that as gardeners we follow the same principles, though in modules, plugs or pots as you prefer.
Depending on the size of the growing medium the lettuce plants can be planted at quite a late stage and hence are ideal as plants to fill in gaps in beds. Plus being grown like this means we can plant late and get more crops into each area when grown successional.
If grown close together in smallish blocks or modules for too long the plants sometimes go a bit leggy. Planted outdoors in this condition they would soon get damaged by the wind and “screw off”. The solution is to “give them a haircut”. Use shears to cut the leaves back shorter before planting. Provided the growing point isn’t damaged the plants survive this treatment very well, certainly better than being battered by the wind.
Block/module grown plants can be pushed into recently cultivated or rotavated ground with ease. There’s no need to use a trowel to dig a planting hole. Just push them into the soil.
And, if like me, you favour No Dig gardening then use a dibber to make holes in your compost and drop a plant in each hole.
Lettuce crops greatly benefit from a good watering soon after planting. It beds them into the soil and encourages root growth and establishment. Commercially I used a raingun that would water a half acre block overnight. But on a garden scale I find a watering can and rose works very well.
Barerooted Lettuce
There is another way to plant lettuce. It’s very low cost but is a bit fiddly. It’s to grow the seedlings in a seed tray and then dib them into the soil when at the cotyledon stage.
Commercially I used to do this when planting in the winter as I had more time and space was not at such a premium.
Between 500–1000 seedlings can be grown in a seed tray, These are teased out of the compost when it is fairly dry and each seedling is individually placed in a small hole in the greenhouse bed. We would rotovate first, then put scaffolding boards on the soil to work from. This slightly formed the soil and made it easy to make a shallow hole in the soil with a finger tip and drop a lettuce in each hole. The trick is to drop the roots in and flick the soil back into the hole and cover the roots in one easy movement. It’s a knack soon picked up when planting up to 100.000 lettuce per year this way! Spacing is achieved by using a string the full length of each greenhouse bay (ours was 120 foot long) and a spacing stick.
The spacing stick is made by cutting a piece of wood about a metre long and gutting grooves in it at the required spacing.
The above sounds cumbersome but is actually quick and easy when you get used to it. Using it we would plant tens of thousand plants a day. And best of all it can be done on a small scale by gardeners. It saves a lot of space in the propagation house, there are no bulky modules to carry around and planting is quite therapeutic. It’s ideal for a lazy gardener like me.
When planting bare root seedlings there is a need to be careful not to damage the seedlings. The stems are easily bruised so hold them between fingertips by the seed leaf.
Promoting Rapid Healthy Growth
Once planted in the soil and given its first watering the lettuce soons settles in and starts to make growth once the conditions are right. In winter, with low light levels and colder conditions it seems slow but still takes place. Smallish lettuce are tolerant of extremely cold weather and under glass I’ve had lettuce frozen solid for weeks at a time only to “resurrect” once the weather turns warmer.
Before planting in the soil I like to add a good base dressing of fertilizer. Personally I prefer an organic fertilizer because it is slow acting and lasts longer. I have a personal favourite, Vitax Q4, but use whatever you wish and follow the instructions on the pack.
Once the lettuce grow away and form a roseate, i.e. the leaves start to adopt a flower-like structure to their shape, growth will speed if conditions are ideal.
Once they start to “meet across the rows” .. and there is little bare soil between the plants they can benefit from some extra nitrogen. Commercially we would add it in the irrigation water or, preferably, we would trickle it between the plants in granular form. In my case I used Nitram, which is 35%N, and would put it in a plastic watering can and trickle it out the sprout, up and down the rows, as I moved almost at a run from one end of the greenhouse to the other.
The above practice has a garden application. On a small scale we can boost growth with nitrogen fertilisers if we wish. They need not all be fed at once. We can feed a few plants each week and this will increase growth rates and reduce the need to sow successive batches of seeds quite as often.
In the No Dig garden there is no need to add extra nitrogen. The compost supplies enough to support all growth. But you might wish to experiment with a little additional nitrogen to control maturity dates!
How to Grow Lettuce: Harvesting Lettuce
Traditionally lettuce were grown to be cut once and once only. Today, in the garden, they are often harvested of a few leaves at a time over many weeks or even months. This practice gives a long season of succulent leaves until such time as the lettuce decides it’s time to go to seed. And go to seed it eventually will. But it’s still a good way to prolong the harvest period and one I’ve adopted since becoming an “amateur”.
Cut and come again lettuce are also grown over a long season and harvested as needed. The seed sold for this purpose tends to be comp[osed of varieties that do not “heart up” and can be grown quite densely.
When to cut is a question I’m often asked. The answer is when they are ready! In the garden that’s whenever we want it to be. Commercially there are however regulations on lettuce size. When I grew them commercially the minimum weight was 6 ounces for a buttehead.
Plant Spacing
The closer plants are grown together the smaller they tend to be. This can be a good thing, especially where we are harvesting leaves over a long period. They require less water and swamp out the weeds. No weeds is something I appreciate as a lazy gardener.
The traditional plant spacings are as follows .. and being traditional I give them in inches!
Lakeland varieties 12×12 inches outdoors.
Crisp .. 10×10 inches outdoors but can be down to 8×8 inches for compact varieties when grown under glass.
Roundhead 9×9 inches under glass or outdoors, In summer I used to decrease the spacing to 8.5 x 8.5 inches under glass. It sounds little different but commercially it increases yield and profit whilst still growing a very heavy lettuce.
Cos 9×9 inches will give a good heavy cos lettuce but if you want them extra big give them 10×10 inches. A full-size cos can weigh 16 ounces (450g) or more.
Growing in Containers
Most of the above advice has applied to growing lettuce, indoors or outdoors, in the soil. But lettuce grow very well in pots, bags etc. Provided there is enough soil, compost or whatever and you can give them enough water they will prosper. I’ve seen lettuce grown at table top level in recycled supermarket plastic bags .. and they’ve been very good crops.
Experiment, Try things for yourself. Lettuce are very resilient and survive most things we throw at them.
Lettuce Problems .. or at least the main ones
Botrytis (Grey mould) is a fungal disease of lettuce. It usually gets into the crop via damaged leaves or stems and is worse in wet conditions and when growth is slow.
The best way to present it is to maintain good air movement, don’t crowd the plants together too much and not damage the crop. Remove infected plants.
There’s no good organic cure but if you are prepared to use chemicals there are fungicides that can be used.
Slugs and snails love succulent lettuce! The only cure is not to have slugs and snails.
Slug Control Methods .. That Don’t Work!
There’s a lot more on slug and snail control on our control page
Aphid also love lettuce. And whereas it’s easy to wash them off of crops such as tomatoes with a jet of soapy water, that’s much harder when they are under the leaves of a densely growing lettuce.
A few aphid aren’t going to hurt the lettuce and can be washed off once harvested. But they have a habit of breeding very fast on lettuce.
Natural predators destroy a lot of aphid but the numbers of aphid need to build up before the predator numbers increase. That’s not great news for lettuce growers.
There are some organic sprays, such as natural pyrethrum, that will kill aphid. However most pyrethrum based insecticides are actually manufactured and hence not natural. They often say based on natural pyrethrum, but that’s not the same thing.
When I grew lettuce commercially I had to take a pragmatic approach and use aphicides. I chose pyrethroids that were of low persistence. The real;ity is that though you and I may tolerate a few aphids on our plates, the supermarkets will reject whole lorry loads of lettuce if they see a single aphid. They blame us, the consumers, and say we will not tolerate it.
More on How to Grow Lettuce
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*In English, according to the dictionary, the plural of lettuce is lettuces. But I’ve never met a lettuce grower that uses the word lettuces. They all say lettuce in both the singular and plural form. As an ex-commercial grower, I use the word lettuce in both the singular and plural form.
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