Lettuces may appear easy, but it can be tricky to get lettuces throughout the year, because they will not germinate once temperatures rise.
When to sow lettuce seeds
Summer sowings can be tricky and the seeds must be sown in the late afternoon and placed in the coolest position you have.
Different lettuces mature at different rates. The fastest are the loose-leaf lettuces such as 'Salad Bowl'. Next come the smaller hearting lettuces such as ‘Little Gem’ and its red-leaved brother ‘Dazzle’. These little lettuces stand well.
The slowest to mature are the upright Cos or Romaine lettuces and these can take a couple of months.
If you have a greenhouse you should sow more seeds at the beginning of September and bed them out for winter picking. No heat is required, but you may have to fleece in cold weather.
How to sow lettuce seeds
- Use small seed trays and sprinkle the seeds lightly on top of ready-watered compost.
- Water again once the seedlings appear. Prick out once the seedlings have four true leaves.
- You can also sow seed straight into modular trays with small compartments. This saves pricking out.
Sow three varieties of lettuce
Select three different types of lettuce to extend the picking season.
- Choose a loose-leaf ‘pick and come again’ variety like ‘Salad Bowl Mixed’ and this soft mixture of red and green oak-leaves will be ready to pick after eight weeks.
- Sow a small, hearting lettuce like ‘Little Gem’ or its red-leaved equivalent, ‘Dazzler’, and it will be ready to cut two to three weeks later.
- Finally sow a slower-maturing Cos variety like ‘Lobjoits Green’ as these often take ten to twelve weeks to fill out.
- Always use fresh packets of seeds with the correct date because lettuce has a short period of viability - three years at most.
- Write out the labels before you start and fill the trays to within half an inch of the rim.
- Water well before sowing using tap water. Ideally the water should stand in a watering can with a fine rose for at least half a day to warm up and release some of its chlorine. Using tap water (ie not from a water-butt) prevents damping off - a fungal disease.
- Sprinkle the large seeds very thinly and lightly cover with a fine layer of compost.
- Place in a cold frame, or in an unheated greenhouse, or on a cool window sill. Ideally seeds will germinate within 6 - 14 days in reasonable temperatures.
- Prick out when two proper leaves show and then plant outside once large enough.
- Repeat the process every 4 weeks until late July to ensure a long supply of salad leaves.
- Lettuce plants make attractive edgings to the vegetable bed and they are also useful decoy plants, or slug magnets, planted close to runner beans.
Best varieties of lettuce to grow in the UK
‘Little Gem’ AGM
The best early small lettuce - hearts up well. If you've only room for one or two, opt for this.
‘Salad Bowl Mixed’ AGM
An early cropper, this decorative green and red oak-leafed variety is a loose leaf variety. Another must for the vegetable garden.
‘Lobjoit’s Cos’ AGM
Large, crisp green-leaved cos suitable for spring and autumn sowing.
Similar in shape to ‘Little Gem’ but with burgundy leaves.
A medium-sized, shiny-leaved red cos lettuce - slow to bolt.
Survives hot summers and produces crisp, dark-green solid hearts - traditionally used in Caesar salads.
Growing lettuce: top tips for success
- Lettuce is a cool-season crop and most varieties struggle to germinate and grow in hot conditions.
- Sow on cooler days or in the evenings if the weather’s hot. Plant out in cooler positions if possible.
- Grow a selection - they mature at different rates and some varieties are much less likely to bolt.
- Once planted out always water in dry weather to prevent bolting (running to seed).
Bolting and mildew in lettuces
Bolting (or running to seed) tends to happen in hot weather and the whole plant becomes bitter and inedible. It’s a lot less likely to happen after midsummer’s day (June 21st) but exceptionally dry summers can still send every lettuce into seed.
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