Leeks: Direct Sow Vegetable or Seedling Plants
How to Sow and Plant
Leeks may be grown from seed or from seedling plants.
Sowing Directly in the Garden
- Sow in average soil in early to late spring for a fall crop. In the Deep South, Gulf and Pacific Coast areas, sow from fall to early spring.
- Choose a location in loose, well-drained soil in full sun where you did not plant members of the onion family the previous year.
- Work organic matter into your soil at least 6-8 inches deep, removing stones, then level and smooth.
- Sow seeds ¼ inch deep in rows 18 inches apart.
- Firm lightly and keep evenly moist.
- Seeds emerge in 14-21 days.
- Thin to 6 inches apart when seedlings are 1-2 inches high.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. Avoid disturbing the soil around the plants when weeding.
- Keep plants well watered during dry periods to promote rapid, uninterrupted growth. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It’s best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated.
- When the plants are about the size of a pencil, wrap the base of the stalks with paper or mound up the soil to blanch them.
- Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
Harvest and Preserving Tips
- Harvest leeks when the bases of the stalks reach ¾-2 inches in diameter, about 90 days after sowing.
- Sever the roots under the stalks and twist the stalks back and forth to loosen them and ease them out of the ground. Cut off remaining roots and all but 2 inches of the leaves.
- Harvest as many leeks as you will use and leave the rest to harvest later in winter.
- Mulch leeks heavily in cold winters.
- Leeks may be frozen after blanching.
Common Disease Problems
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Onion White Rot: This soil-borne fungus causes yellowing and wilting of foliage above ground. Below ground, the roots rot and the fungus also infects the bulb. At the base of the bulb, a white fluffy fungus will appear with black fungal bodies. Burpee Recommends: Remove infected bulbs. Practice crop rotation with members of the onion family.
Pink Root Rot: A fungus that attacks roots causing them to turn a light pink, then red and eventually purple-brown and causing them to shrivel. Infected plants show signs of nutrient deficiencies and drought because the roots cannot take up water and nutrients. Plants are stunted. The disease lives in the soil for several years and thrives in warm temperatures. Burpee Recommends: Plant as early as possible so the bulk of the plant growth will be in cooler temperatures. Rotate crops and plant resistant varieties.
Rust: A number of fungus diseases that cause rust colored spots on foliage, stalks and husks. Burpee Recommends: Plant early as these diseases tend to be worse later in the season. Plant resistant varieties. Practice crop rotation. Remove infected plants.
Common Pest and Cultural Problems
Leafminers: These insects bore just under the leaf surface causing irregular serpentine lines. The larvae are yellow cylindrical maggots and the adults are small black and yellow flies. They do not usually kill plants, but disfigure the foliage. Burpee Recommends: Remove affected foliage.
Leek Moth: These insects feed on the leek plants, and may cause secondary damage as fungal and bacterial infections can cause the bulbs to rot. The adults are ¼ inch long brown moths, and the caterpillars are ½ inch long, creamy white with a brown head and small legs. The caterpillars tunnel into the leaves causing yellow and brown patches, and eventually bore into the stems. They emerge and spin a silky net on the foliage. Burpee Recommends: Use floating row covers. Hand pick caterpillars. Rotate crops. Remove plant debris.
Onion Maggot: This insect causes stunted or wilted seedlings and damaged roots and bulbs. The adult is a greyish colored fly which lays its eggs around the base of the plant. The maggots bore into the roots. Burpee Recommends: Remove all bulbs at the end of the season and remove all volunteer wild onion plants. Floating row covers can prevent the females from laying eggs. Check with your Cooperative Extension Service for pest controls.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls.
What is blanching? Blanching is to turn something white. In the case of leeks, it is covering the lower stem to keep it as white and tender as possible.
Can I grow leeks in containers? Yes, leeks are fine in containers. Be sure to use a commercial potting mix rather than garden soil.
Are leeks perennial? No, leeks are biennial, but we grow them as annuals. Once they produce a flower the second year they are not good for eating.
How can I use leeks as companion plants? Plant leeks with carrots, radishes, onions, celery and beets. Do NOT plant near legumes such as beans and peas.
How many leeks will I get from each plant? Each leek plant produces one leek. Be sure to separate the seedlings when planting.