Leeks take a long time to grow and need a fair bit of space but what would winter be without leek on the menu?
Leeks are a traditional winter veg and are ‘in season’ from October to March. They can be sown from February to May for full-size leeks, a little later if you are happy with baby leeks. When choosing varieties check the harvest time because some are hardier than others and better able to stand the winter in the ground. If you are aiming to grow show leeks then you need to sow early and you have a choice of blanch leeks and pot leeks. Blanch leeks have a long, lower white part, which can be extended by growing in tubes and pot leeks have a broad, stumpy white part. But these are specialist crops.
Leeks are easy to grow but there are some issues and some tricks. Firstly, they are prone to white rot, a soil fungus that also affects onions. It causes the plants to rot at the base and makes it impossible to grow leeks. If you want to, you could grow some in pots or a raised bed that is not in contact with the infected soil. Leeks also get the fungal infection rust. This causes brown spots on the leaves. It is tricky to control, though some strains are resistant. It does not affect the eating quality of the plants if the rust is not severe but in wet weather it can kill the leaves. A more recent problem in the UK is leek moth which destroys the plants as the grubs bore into them. In areas where it is common leeks should be grown under fleece or mesh.
Having got the problems out of the way, back to growing. The soil in which leeks are grown must be well dug and ideally well manured the previous year. Soil pH is not critical but I have always had the best crops when the soil had been recently limed. Clay soils are not a problem but bear in mind you will be digging them out of the soil in January.
I usually do not sow very early because I don’t need leeks while I am picking runner beans, though I have just sown a small amount just for the hell of it. I prefer to sow in a row in the garden in late March or April. Take out a drill (shallow trench) and sow the seeds thinly along this. Cover and water and keep moist until the seedlings appear. The seedlings should be left to grow unless they are too crowded in which case you can transplant them into gaps in the row when they are small. When the plants are about 25cm high and some are as thick as a pencil (they will never all be that size) you are ready to transplant them. If you do not transplant them and leave them to grow where sown they will not have a long blanched (white) stem section.
Get the ground ready for planting by forking it over, firming and raking and scattering a general fertiliser over the surface. Water the leek seedlings the night before and you are ready. Dig up the seedlings and pull them apart. Trim the roots so they are about 5cm long (not essential) and trim off the top of the foliage. Then make the planting holes. These should be about 20cm apart in rows 40cm apart. To avoid compacting the soil I use a board to tread on, which also makes a line to work along. Make holes about 15cm deep. I do this with the end of a rake or hoe handle. You can wrap masking tape around the handle to help gauge the depth of the holes. Avoid planting in very dry soil of the holes will not ‘stand’. After making the holes, drop a plant into each (the root trimming helps make this easier). Then pour some water into each planted hole to puddle them in. And then off they will grow. A second watering may be needed in very dry weather but otherwise they need little extra care apart from keeping them free of weeds.
Seeds can also be sown in trays, early, and either left to grow big enough or transplanted twice.