Blanching Leeks and Harvesting
Blanchingincreases the proportion of plant which is edible, and improves the flavour, which would otherwise be strong and fairly harsh. Begin blanching in early mid-autumn; it is a gradual process and should be done in several stages, rather than all at once. There are several methods of blanching, depending on the way in which the leeks are growing.
If your leeks are growing in a trench, blanching consists of gradually filling the trench withto the bottom of the lowest leaves each time, until the plants have ceased to grow, which will probably be mid to late autumn, depending on the weather. This should give you 10-15 cm (4-6”) of blanched stem at least. One word of advice, however: the soil used for earthing-up must be dry, friable and very fine textured. If it is wet when earthed-up, rot is liable to set in. If the soil is lumpy, it will be difficult to handle and will not exclude light properly.
If grown on the flat, push the soil up around the plants, increasing the soil depth by about 5 cm (2”) each time. You can keep the stems free of soil by using collars, which are secured around the leeks up to the base of the leaves. Various materials can be used for the collar: lengths sawn from plastic piping, clay drain pipes, or, at virtually no cost, pieces of strong brown paper secured with string or rubber bands. If you use paper tubes, support them with bamboo canes. Whatever form of collar you use, the minimum diameter should be 7.5 cm (3”); they should be 30-37.5 cm (12-15”) long.
Attach the collars before carrying out the earthing-up process. As the plants grow, draw up more and more soil with a hoe, fitting another collar above the first one.
Although it is not strictly necessary, you can put planks of wood, on edge, along both sides of the row instead of using collars. This forms a sort of box into which the soil is put, until the desired height of soil is reached. With this system, you can use silver sand, leafmould or peat instead of soil.
Harvesting and aftercare
Leeks may be harvested from mid-autumn through to the end of late spring, depending on time of sowing and variety. The hardier varieties are left where they grow until needed. Never pull leeks out of the ground by brute force, or they will more than likely break in two, leaving you with a handful of leaves. Instead, lever them out of the ground with a spade or fork. Take the largest first; the smallest, if left until the spring, will put on some weight before running to flower. If the ground is, likely to be frozen for long periods of time, it is a good idea to lift any leeks which are ready and store them in sand in a cool place, where they will keep for about a month. If, towards the end of the season, you have a few leeks still in the ground, but need the plot cleared for new planting, you can dig the leeks up and heel them in a shaded place, until needed. Lay them on their sides in shallow trench with the top part of the leaf stalk projecting above the ground, covering the rest of the stalk with soil. This also helps to stop them bolting.
You can, by leaving leeks in the ground and nipping out the flower stems, get a bonus crop: leek bulbs. These small white bulbs will form at the base of the plant; harvest them in early summer and use asor .
If you grow prize-winning leeks and want to keep a particular strain for future show work, allow one or two leeks to flower. Tiny, complete plants, or ‘pods’, will form among the seeds on the seed pod; these can be detached and potted on in the greenhouse.