Leeks

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Leeks are part of the large onion family (Alliaceae) but are much quicker and easier to grow than onions. They are ready to harvest from 14 weeks from seed.

Leeks have thick, white, onion-flavoured ‘stems’ (actually leaf bases) that are usually prepared by being sliced. They are used to add a gentle onion flavour to foods or can be turned into their very own dish of potato and leek soup.

Leeks can be substituted for onion. They are low in calories but high in magnesium and vitamins A, C, and K.

Follow our seven easy steps to successful leek harvest including tips along the way.

Seven handy tips on how to grow yummy leeks for your favourite recipe

When to plant

Like onions, leeks are cool-season crops that grow best between 13°C — 24°C.

  1. In cool and temperate areas sow seed from late spring to autumn. Seedlings are planted through autumn and winter.
  2. In tropical zones, leeks are grown as a dry season crop, sown in autumn and early winter.
Seven handy tips on how to grow yummy leeks for your favourite recipe

Location

Leeks can be grown in most parts of Australia. Check with garden centres and hardware stores for varieties available in your local area.

  • Plants grow best in a full sun position in soil that holds moisture well.
  • Too much shade, especially as days shorten in winter, can cause leeks to become spindly with thin stems that may be prone to pests such as aphids.
  • Leeks can also be grown in pots; ensure they are given enough space between each seedling for proper stem development.
Tips for spring soil care - understand soil fertility

Soil

Get the soil right to harvest a bumper crop of tasty leeks

Follow our steps for easy soil preparation.

How to grow vegetables - Broccoli

Step 1 – Sowing seeds

  • Seeds can be sown directly into the ground or seed trays.
  • In the ground, grow from seed sown directly in well-prepared, moist soil at a depth of 6mm. Space 15- 30cm apart.
  • In seed trays, sow into individual seed cells or punnets to then transplant in around six weeks.
  • Water in well with Seasol or Seasol GOLD to help increase seed germination rates. Mix 30mL of concentration per 9 litres of water (standard watering can).

Note: These are not leek seeds, it’s just an illustration to show the process.

Step 2 – Germination

  • Seeds will take 10-14 days to germinate depending on temperature. Watch as the tiny leaves come through the soil.
  • Thin the tiny seedlings to 5cm apart when they are about 5cm high to reduce overcrowding and poor root development.
  • To avoid root disturbance, use scissors or tweezers when thinning seedlings.
  • Liquid feed with PowerFeed PRO Series for Tomatoes & Vegetables every 2 weeks for strong healthy growth. Mix 20mL of concentrate per 9 litres of water.

Step 3 – Leek seedlings ready for transplant.

  • Transplant your own seedlings when they are large enough to handle (around 12cm high) around 10 weeks after sowing seed.
  • Space seedlings 15-30cm apart and firm into the ground.
  • If planting from a purchased punnet, follow the directions on the plant tag and push the soil firmly around the roots of the seedlings.
  • Water your newly transplanted seedlings in with Seasol to get them over the transplant shock and for strong root development and healthy growth.
Seven handy tips on how to grow yummy leeks for your favourite recipe

Step 4 – Blanching seedlings

  •  For white or ‘blanched’ stems follow these alternative growing methods. Plant seedlings in trenches around 15-20cm deep. Cover the roots so the plants are stable but not buried.
  • Gentle watering washes soil in around the stem. As the seedlings grow, earth up soil around the stem.
  • Other methods of blanching include growing leeks in tubes made from piping or recycled milk cartons.
  •  Place these items around the plant to exclude light from the base of the stem so it stays white.
Seven handy tips on how to grow yummy leeks for your favourite recipe

Step 5 – Leek growth

  • As leeks grow, keep the soil around the developing plants hand weeded or hoed.
  • Spread pea straw or sugar cane mulch around each plant to suppress weeds.
  • Leeks like to stay moist so check soil moisture daily. If possible, water early in the morning.
  •  Every 6-8 weeks apply another application of PowerFeed Controlled Release for Tomatoes & Vegetables to produce plump stems.
Seven handy tips on how to grow yummy leeks for your favourite recipe

Step 6 – Ongoing leek growth

  • Liquid feed to encourage fast growth and plump leeks using PowerFeed PRO Series for Tomatoes & Vegetables applied every 1 to 2 weeks.
  • Leeks that are water stressed may be tough and can bolt to flower so continue to water regularly.
  • Check mulch and increase the depth as the leeks grow. This also limits the amount of dirt that can find its way into the stem.
  • Check for pests daily as the leeks mature. Carefully examine stems as there are many layers where pests can hide.
  • Leave the leeks in the ground and pick them on the day you plan to eat them. Remember the quality will start to deteriorate around the flowering stage.
Seven handy tips on how to grow yummy leeks for your favourite recipe

Step 7 – Leek harvest

  • Leeks are ready to harvest when they are 2-2.5cm thick or around 12-18 weeks from transplanting.
  • Harvest stems as needed (but before flowering). Wash then chop off roots and tough leaf tops.
  • Leeks can be gritty if soil has worked its way between the leaf sheaths.
  • To remove dirt, pull away the tough outer leaves, make vertical cuts in the stalk then wash well.

Things to watch out for…

Well-grown leeks have few pest problems. Diseases are generally kept at bay by correct spacing at planting and keeping the growing area weed free. Some problems that can occur include:

  • Aphids These tiny black or green pests cluster under leaves. Squash or hose off.
  • Onion thrips Minute insects that cause white flecking on the leaves. Remove worst affected leaves and increase watering to compensate for feeding damage.
  • Slugs and snails These pests can destroy young plants. Snails and slugs are active at night; squash those that are seen. Use iron-based, non-toxic baits to control them.