How To Grow Leeks

LEEKS (Allium porrum)

Leeks are related to garlic, chives and onions. Leeks produce a long cylinder of bundled leaf sheaths. The green leaves and the white elongated bulb are both used in cooking. Leeks are a good source of vitamins A, B6,C and K. They also have calcium, manganese and magnesium which gives them antibiotic and anti-cancer properties among other benefits.

Ecology

Altitude: Grows well in altitudes of upto 2500m above sea level.

Annual rainfall: 650-800mm

Temperature: 15-25 degrees celsius

Soil Type: Fertile, loose, well draining soil

Soil pH: 5.0-6.8 

Sowing Method

Varieties: Italian giant, Bulgarian giant, American flag, Carentan, Giant musselburgh, Swiss bluveta

Seed Rate: 1.2 kg per acre

Sowing Depth: Sow seeds about 2 cm apart in shallow furrows and cover lightly with soil.

Germination Period: 7-10 days

Transplanting Period: Seedlings are ready for transplanting 8-10 weeks after sowing when they are at least 15-20cm  tall.

Spacing: Plant to plant 10 cm

Row spacing 20cm

Depth 15 cm

Light Requirement: Full sun

Water: Leeks have shallow root systems therefore require consistent moisture. Regular watering should be done at least 1 inch of water per week.

Feeding:

Seedlings

Prepare the nursery bed by adding well decomposed manure or compost and mixing it with the soil. After sowing, the nursery should be drenched with a seaweed fertiliser to break seed dormancy and ensure uniform germination. Subsequent applications of seaweed should be done every 14 days at a rate of 5ml per 20 litre of water until transplanting.

Transplants

Apply manure at the rate of 2-3 tonnes per acre into the final planting beds/field at least 1 month before planting. Add bone meal fertiliser at the rate of 2kg/10 square metre. Apply humic powder into the beds/field at the rate of 5kg/acre or mix it with manure at the rate of 1kg humic powder into 1 ton of manure before application.

Compost can be used as an alternative to manure. Apply a thick layer of compost about 1-3 inches before planting. Compost should also be added as a topdress throughout the growing season.

Seaweed fertiliser should be sprayed as a foliar feed at the rate of 10ml per 20 litres of water at 15 day intervals throughout the growing season.

Harvest period: 90 days

Harvesting and Storage:

Harvesting can begin 90 days after planting and can continue until the harvest is complete or the weather makes further harvesting impossible. Leeks can tolerate standing in the field for an extended harvest which can take place upto 6 months from planting. Leeks are best enjoyed fresh therefore only the needed leeks should be picked and the rest can continue growing. The unharvested leeks grow larger and more flavourful.

Harvested leeks should be placed in boxes or containers that allow free circulation of air inside. The boxes or containers should not be overloaded.

Leeks need to be pre cooled immediately after harvesting. This involves bringing the crop to about 2 degrees celsius and a humidity of about 100%. When the leeks are kept under these conditions they can be stored for between 2-3 months.

Common Challenges:

Pests

Onion fly– The adult fly looks like a small grey house fly. The larvae, which are creamish white maggots feed on the lateral roots, then tunnel into the taproot and sometimes bore into the base of the stem. Infested leaves turn bluish and eventually wilt. The plant becomes shrivelled and dies. The maggots are also found inside developing onion bulbs. Their feeding exposes the plant to infection by diseases like soft rot.

Leek moth (onion leafminer)– the young, pale green caterpillars tunnel through the leaves to feed, which are disfigured with whitish brown streaks. As more and more tunnels are made, the leeks lose their strength and may collapse and die. Older caterpillars tunnel down into the stem of the leek causing extensive damage, which may cause the leek to collapse or rot from within.

Cutworms– These are brown or black caterpillars which live in the soil. They cut and eat the stems of young seedlings and transplants. Heavy infestations can cause total crop loss.

Onion thrips– these are the major insect pests of leeks which cause white flecking on the leaf surface and a drastic reduction in foliage quality as they feed.

Diseases

Damping off– this is a soil borne disease which attacks the seeds and seedlings. Infected seedlings may fall over and die due to rotting of plant tissues at the soil level, while affected  seeds do not germinate.

Downy mildew-the infected leaves turn pale-green, then yellow, and collapse and eventually die. The pale-green and yellow stage is characterised by oval-shaped lesions that often become infected with other diseases. This disease is favoured by cool and humid weather.

Purple blotch– infection causes formation of small water soaked lesions with whitish centres, mostly on the older leaves. These lesions enlarge as infection progresses and become purplish with light yellow concentric rings on the margins. If the disease is not controlled, leaves may turn yellowish-brown, lose erectness and eventually wilt.

White rot– infection is most noticeable in hot, dry conditions and plants grown in overcrowded conditions are more vulnerable. The infected leeks have yellow leaves, with a white or grey fungus covering the underground base of the plant, looking like strands of white thread.

Leek rust– leeks growing in wet soil which is rich in nitrogen but lacks potassium are particularly vulnerable. The symptoms of leek rust are orange, powdery spots on older leaves, which later turn yellow.

Botrytis leaf blight– symptoms on the leaves initially appear as greyish-white, oval-shaped spots which are usually surrounded by a silvery white halo with uneven margins. The centres of most of the spots become sunken and straw- colored. In severe cases, tips of the leaves begin to die back.

Tips:

• Seedling roots should be trimmed to about 5cm long and the tips chopped off while transplanting.
• Leeks are poor competitors with weeds and therefore the field should be kept weed free. Weeds also harbour pests and diseases. Mulch can be applied to suppress weeds.
• Planting leeks in deep holes helps  in getting longer stems. This can also be achieved by hilling soil around the stems or by covering the stems to keep the area dark and keep out sunlight thus producing longer stems. This process is called blanching.