Plant Description
Leeks are part of the same family as onions and while they share some of the same production practices as onions, they are a more sensitive crop to handle and market effectively. Leeks originated in central Asia and later moved westward into Europe where their popularity as a vegetable grew and spread to the rest of the world.
Leeks have the advantage over onions that there is no ball or bulb that has to form or ripen and therefore leeks can be harvested and consumed from very early in their growth cycle.
Uses
The part of the leek that is the favoured part of the plant is the white stem or shank. When the plant is growing, this is situated just below the soil surface where the leek leaves are bunched into a tight roll of tender leaf. As they mature leaves grow out, they become tougher and are less palatable.
The young baby leeks can be eaten whole as the leaves are still soft and tasty. The leek is boiled, steamed or fried and consumed on its own or together with other vegetables or proteins. The young tender leeks can also be eaten raw in salads. Leeks are very healthy and a good source of vitamin A, C, E, K and calcium.
Soil Requirements and Preparation
Leeks are grown most successfully in a medium textured loam soil that drains well and is rich in organic material and nutrients. Rough sandy soils are not suitable as grains of sand can get trapped in the white overlapping leaves below ground making them less palatable and thus less marketable.
Also, dark heavily textured clay loam soils tend to stain the white leek stems so should be avoided. The first action when setting out to plant any crop is to take a representative soil sample of the area that is to be cultivated and to have it analysed by a reputable soil testing laboratory.
When the results of the soil samples are received they will show what is required in the form of lime for pH and other nutrients and trace elements that will be required to make the crop a success. The pH of the soil should be between 6.5 and 7 and if the soil is too acidic or below 6 pH, then the required amount of lime can be broadcast and ploughed into the soil to raise the pH of the soil.
This should be done at least eight weeks before planting. This ploughing process also incorporates the previous crop residue and any green cover crops that may have been planted. Four weeks prior to planting add trace element requirements like Boron, Zinc and Manganese and any additional organic manures or compost and work this into the top 400 mm of soil.
Follow with a disc harrow to further chop up and till the topsoil to prepare a clean, level area for planting. In the final week before planting seedlings, apply the pre-plant fertilizer and disc harrow this into the top 20 cm of soil to prepare for the planting.
This final tillage will also get rid of any weeds that may have started to grow. Lightly irrigate the area before planting the seedlings. For direct seeding also disc plough the plant area in the final week before planting to clear weeds and prepare seedbed but without a pre-plant fertilizer and plant seeds onto dry soil and irrigate lightly after seeds have been planted.
Climate
Leeks are a cool weather crop and grow well in a temperature range of from 12°C to 25°C. They are not suited to growing in temperatures higher than this. When temperatures exceed this, leeks will mature and harden rapidly, making them unsuitable to harvest.
Leeks are frost resistant but excessively cold weather will also slow growth and affect the production and quality of the leek.
Varieties
In the past, only a few main varieties of leek were produced commercially. More recently there are many new varieties including new hybrid varieties that grow faster and stronger and these are replacing the traditional varieties.
There are well over 100 varieties and the best way to decide what to plant is to seek the advice of the local extension officer and seed merchant for the best variety for the particular growing conditions.
It is also imperative to get the market-related advice from the buyer of the product. Some popular varieties are: American Flag, Armore, Atal F1, Bulgarian Giant, Carentan, Dawn Giant, Italian Giant and Musselburg.
By Louise Brodie