May has turned chilly and wet, so today I’ve been looking for excuses not to do all the gardening I need to do, hence this article!
One of the things that does love cool weather is lettuce: it won’t even germinate above 21°C (70F), so it’s best to start it off whilst it’s still cool.
When I first started gardening, I tried growing lettuce in the ground, in traditional neat rows like I saw in books. It was a bit of a disaster: all the green leaves (Cos) got eaten by slugs, whilst the slugs avoided the red leaves (Batavia), but then so did we, since they were really quite bitter!
Subsequently, I’ve discovered the secret to growing enough lettuce to keep you in interesting leaves all year is to plant a mix of varieties in containers.
Planting in containers means you can put them out of the reach of slugs, perhaps applying a bit of copper tape to the sides, or placing on a window-sill, door-step, or just paying them more attention and picking off slugs and snails at night, to avoid too much damage. You can also move containers around the garden with the season, seeking the shade during hot periods, and you can also efficiently water and harvest them. If you haven’t got much outside space, then of course, containers are your go-to solution.
For your container, you want something that’s going to be big enough to supply you with enough leaves to make it worth while, and to not dry out too easily: the sort of ‘live lettuce’ trays you buy in a supermarket is about a tenth of the surface area and a quarter of the depth you want! I usually grow in a trough about 30cm wide and deep, and 60cm long.
You can, of course, grow in containers less deep, such as seed trays or re-used trays from packaging, but be aware that you will need to water much more often, as salad leaves soon go to seed and stop growing nice leaves if they are stressed by drying out. Equally, ensure that your container has sufficient drain-holes in the bottom, since otherwise the roots will rot if the British summer delivers its normal quantity of rain, or you accidentally over-water.
Sowing a mix of varieties, as a ‘cut and come again’ crop means that you never get bored of a single variety, and gives a chance to try out some interesting leaves, without ending up with a crop nobody wants to eat. Retailers sell traditional ready-mixed ‘salad bowl’ leaves, and themed mixes such as Italian (usually with Salad Rocket) or Oriental (usually with Pak Choi and Mizuna), or you can buy a couple of varieties you know you like, and mix them yourself.
Be aware that some varieties are more vigorous than others, and this will affect the productivity of the less vigorous varieties: for instance, I’ve found it’s best to grow Mizuna (Brassica rapa var. nipposinica) on it’s own, since it will out-compete anything else (it also crops longer than anything else, and resists slugs, though is a bit too coarse on its own).
For sowing, choose a good, reasonably fine compost (I prefer a peat-free composts), fill your container to about an inch off the top, and gently firm the surface before watering with a fine spray.
Scatter your seeds reasonably densely: you are looking for something like two or three seeds per square inch; then cover with just enough compost that you can’t see any seeds – don’t bury them too deep.
For best germination, put the container outside, in a shaded spot, and make sure it never dries out, without making it soggy. You should see germination in about a week.
Once the seedlings have grown several leaves each, and are starting to jostle for space, you can start harvesting. To maximise your crop, try not to damage the centre ‘growing tip’ of the plant – the bit where the baby leaves grow from, as the plant will stop growing without it. Cut individual leaves, or carefully trim a block with scissors if you’re in a hurry. Aim to thin-out the leaves and allow more to grow in their place.
With careful harvesting, and regular watering, you should be able to have fresh leaves for up to three weeks. Once the plants start getting weak, or if they start flowering, it’s time to move on: for a continual supply, try sowing another container about three weeks after the first.
If the plants do start flowering, remember that you can eat the buds, flowers, or indeed the whole plant, so make the most of it!
You should be able to sow lettuce all through Spring and into Summer, and then again once mid-summer has passed. Lettuce is one of the earliest, and the latest, crops you can grow, and you can even over-winter some the oriental ones in a cold-frame, unheated green house or conservatory.