Growing leeks is easier than growing onions, plus they’re extremely space-efficient and hardy (mostly!) through the winter. Leeks should be on everyone’s ‘what to grow’ list. They’re ideal for gardens that aren’t quite as big as you’d like them to be – and, if you get several varieties, you can harvest them from late summer right through winter and into May the following year.
As with many vegetables, there are a few tips and tricks which could make the results even better – read on!
Sow leek seeds in mid- to late March in a 20cm pot in a light, well-drained loam. Leek seeds should be sown shallow, 5mm deep at the most, and kept moist and cool. It’s difficult to sow the seeds evenly and some thinning will almost certainly be required later. This is best done by carefully cutting through the stems at soil level with fine scissors when the seedlings are quite small, as pulling them out will disturb those nearby. This may mean that enough of the plant survives to continue to grow, but if so it will be much smaller than the ones you plan to keep and is not likely to be a problem. Thin so that roughly 1cm of space exists around each plant. Yes, that’s crowded – but it doesn’t matter. Leeks are tall and thin and don’t spread out, so they really don’t need very much space at this stage.
A liquid feed every few days will help keep growing leeks strong and healthy. Keep them moist, and don’t leave the pot sitting in the sun where it may get too hot.
By early June they should be sturdy little ‘pencils’ and can be planted out.
But first, use scissors to cut off roughly half the height of the plant. Then carefully tease the root ball apart – at which point the advantages of using a light sowing medium become clear. Gently pull the leeks from the root ball and then snip off about half the length of the roots. Weird, yes: this is called the ‘top and tail’ method, and while seeming both odd and counter-productive – after all, you just clipped a load of growth off your seedling – it really works. Check this yourself: leave a few with leaves and roots intact and then compare the results later. You’ll be amazed.
Use a stick to make a hole where the leek will be planted. Push the stick into the earth to about 15cms and rotate it a bit to make the hole bigger. Doing this also firms up the sides. If lots of bits fall into the hole – which will make planting at depth impossible – gently flatten out the surface with your hand first.
Drop the leek into the hole – you shouldn’t need to push. The hole should be deep enough to allow good stem growth but not so deep that the leaves completely vanish from sight! At least 5 cm of the plants should poke out to get the light.
Next, don’t fill in the hole! This is very important. Instead, water the leek in with a small watering can, so that a little earth is washed down onto the roots – and that’s all there is to it.
Growing leeks at least 12-15cms apart in rows at least 12-15cms apart should give you high plant density without high disease risk. Add a top dressing of compost while they are still small enough to reach between them. Keep the bed well weeded, as not only will weeds take valuable nutrients they may also create a humid environment which could promote leek rust (see below) and provide habitat for slugs. Oddly enough, slugs can be a real pest on growing leeks and other alliums.
Leek rust is caused by a fungus. Orange, raised spots appear on the leaves. Affected plants should not be composted but burned, and alliums should not be grown in the same bed for at least one year, or two if possible. There is no known cure, but it will really help if your planting is spacious enough to provide good ventilation. Also, try to avoid a high nitrogen / low potassium mix in the earth. Watering every week or so with tomato feed is ideal.
Leeks can generally survive light frosts without too much trouble, but if it’s cold enough for the outer layers to actually freeze then when the thaw happens they’ll not recover. Instead, they turn to a slimy mass inside which your leek is trying to survive. A straw mulch will help, as will horticultural fleece – which should be supported to avoid frosted contact points where it touches the plants.
If you are worried about the coming weather and have a polytunnel or greenhouse, leeks can be dug from the outside bed before the frost hits and ‘heeled-in’ under cover. This simply means digging a shallow trench and putting the leeks into it, with almost no space between them, before back filling the trench to cover the roots and watering them in. They don’t actually grow at this time of year, and this method is enough to keep them fresh enough for use.
Early varieties can be harvested in late August and September, while late varieties can continue the harvest into spring and even into May. However, by June even the latest varieties will be bolting.