Leeks have been cultivated in Egypt for over 3000 years. They are known scientifically as Allium porrum, are related to garlic, onions, shallots and have a more delicate, mild and sweeter flavour than onions.
Growth habits and planting needs
Leeks prefer to be grown in full sun but will tolerate some shade.
The soil should be well drained and enriched with well rotted compost and aged cow manure. Leeks prefer a sightly alkaline soil between 6-7 so amend with lime if your soil is acidic. Dig the soil over well removing any clods or stones, to a depth of 40 cm.
Leeks should follow fruit groups in the crop rotation system because they need potassium but not so much nitrogen.
In Sydney, sow the seeds into trays in February/March or August/September.
Sow the seeds 12 mm deep in seedling trays or punnets, using a good seed raising mix and keep moist. They should germinate in 10 -14 days. Continue to keep moist. Make successive sowings every few weeks to ensure a constant supply over the growing season.
Transplant the seedlings when they are 20 cm in height, about 8 weeks from germination. In Sydney this is April/May or October to December.
Prepare the site for planting by digging trenches 20 cm deep. Gently place the leek seedlings into the trench being careful not to damage the young roots, spacing them at least 15 cm apart in rows that are at least 30 cm apart. Leeks have root systems that spread more than onions and so need the extra space. Gently fill the trench and water gently.
Mound the stem with soil as the leeks grow to increase the white part of the leek.
Keep well watered to allow plant to grow evenly and mulch around the plants away from the stem to conserve moisture as the root system of the leeks is just below the soil level.
This diagram from Root Development of Vegetable Crops by John E. Weaver and William E. Bruner shows the root development (grid in ft) under optimal conditions. It also shows the importance of keeping weeds away to prevent competition with surface roots.
Feed the leeks monthly with fish emulsion until ready to harvest.
The leeks will be fully matured and ready to harvest 12-14 weeks from germination and the stems are 2.5 cm in diameter. You can however, choose to harvest at any time they are thicker than your thumb. In fact, leeks can be left in the ground for some time if needed in temperate climates.
Seedlings transplanted in early Spring will be ready to be harvested in late Summer and those transplanted in late Spring will be ready in Winter.
Loosen the soil around the leeks to make harvesting easier and preventing damage to the leeks. Pull out by gripping firmly and shake off the dirt from the roots.
Do not trim the roots but trim the leaves back.
Store the leeks unwashed and not trimmed in loose bags in the refrigerator for up to 2 weeks. They are at their best if harvested as required and used soon after harvesting.
When cooking, wash thoroughly, then slice in half and rinse between the leaves well to remove any dirt.