Written by Lars Lund 24 Feb 2023 14:05

Growing leeks

Have you ever bought a tray of leeks and gotten too many? You can always find an available space in your garden, perhaps in your perennial bed?

You can choose from autumn leeks and winter leeks. As the names imply, autumn leeks are harvested in autumn, while winter leeks are more tough and can easily withstand frost. Autumn leeks can withstand some frost too, but not over a longer period of time. Autumn leeks are typically longer, while winter leeks are fatter and a little rougher looking.

Inside or outside

Leeks can be sown in your greenhouse in late March. If you are sure there will be no frost, you can already start in January. If you are sowing inside and they are placed in a chilly spot, you can also start in January. Remember that they have to get used to the cold later on, so before permanently planting them outside, put them outside during the day but move them back inside during the night for about two weeks.

It is a good idea to use a seed tray with a plastic lid. It keeps the moisture and protects the seeds against the cold. Alternatively, you can use a box made of polystyrene and cover it with clear plastic.

Leeks love compost. If you have any converted compost, use it as a bottom layer and place 4 inches of sowing soil on top. If you don’t have compost, sowing soil by itself is also fine. Gently press the seeds into the soil and sprinkle a thin layer of soil on top. The soil must be a little moist.

Planting out

If you are sowing outdoors, wait until May, but be aware that the leeks probably won’t grow as big. May is also the time to plant your pre-germinated leeks from the greenhouse or from your home in the garden. Some wait until the beginning of June to avoid the first generation of moths or flies, that can harm the leeks.


Keep your distance.

You can thin out your leeks while they are in seed trays in the greenhouse or when you plant them outside. Dig a trench, approx. 4 ft deep and plant the leeks in the middle of it.

If you prefer the white part of the leek, you can pile up some soil around the leeks as they grow. Alternatively, you can buy sorts, which have a sturdy white shank to begin with. The whole leek is edible, however, most prefer the white shank, even though it contains less vitamins.

The soil must be loose and contain a high pH-level. For that you can add a little chalk to the soil.

A little trick

An old trick I learned many years ago from one of my readers, was to take a toilet roll and place it around the leeks. This way, everything inside the roll becomes white.


As opposed to onions, leeks need a lot of fertilizer in the form of compost or organic fertilizer. To get the most out of it, the fertilizer should be worked into the soil before the leeks are planted out. Grass clippings are an excellent fertilizer as well. However, in the beginning the leeks grow slowly and don’t need fertilizer until June or the beginning of July.

When planting the leeks outside, make sure they are watered properly. Later they require less water, but of course they still need to be looked after. It is also important to remove any weed.   



Autumn leeks are harvested in autumn and winter leeks in the winter months. You can replant the winter leeks in your greenhouse to avoid frost. They can withstand frost, but they get a little chewier. Are the leeks placed outside, put a layer of leaves around them.


Leek moths can harm the leeks. Avoid the first generation by waiting to plant the leeks outside until June. By that time the first generation will be gone. Alternatively, you can use plant netting as protection. You can take the netting off in the beginning of June, but you should put it back on in August and October when the next generation of moths is born.

Leek moths ruin the plant tissue by feeding on the leaves. There is an organic insect repellent that you can pray on the leaves when you spot the first larvae. The larvae lose their desire to eat when they get in contact with the insect repellent.

The leaves can also get red spots, called rust. However, they only occur on the outer leaves and the rest of the leek remains eatable.

Leeks thrive with carrots, beans, celeriac, and broccoli and preferably calendula.