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Kohlrabi

Kohlrabi is an oddball in the vegie garden. It is a curious looking white or purple vegetable with a round bulbous base which is actually the thickened stem base spiked with leaves.

Stripped of its leaves it looks like a space ship. It is part of the huge brassica family and unlike its close relatives such as kale and broccoli, has not yet become trendy as a ‘superfood’. However, if you want to grow something completely different, this is one for you.

Kohlrabi is well worth growing. It has a swollen stem base, which may be purple or white, and tufts of green leaves. The stem is crisp and sweet can be eaten in many ways. It is rich in vitamins (especially vitamin C) and potassium. It is also a good source of dietary fibre

The main varieties offered in Australia are white or purple. The white form is usually sold as ‘White’ or ‘White Vienna’ and has greeny white skin and white flesh. The purple form is known as ‘Purple’ or ‘Purple Vienna’. It has purple skin and white flesh. Both are heirloom varieties that date back to 1859.

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

When to plant

Like other brassicas, kohlrabi does best in a cool climate but is also worth growing through winter and early spring in warm temperate, subtropical and tropical climates. Check with hardware and garden centres for advice on your local conditions.

  1. It can be slow to germinate in very cold or very hot conditions.
  2. Protect young seedlings from heavy frost. In the cooler parts of southern Australia delay planting until August.
  3. In warm zones, plant in autumn or winter; avoid planting in the middle of summer.

Location

  • Plants grow best in full sun or with light afternoon shade in hotter temperatures.
  • They will flourish in soil that holds moisture well.
  • In crop rotation, kohlrabi and other brassicas can follow legumes.
  • They can also be grown in large containers if space is limited.
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Soil

Get the soil right to harvest a bumper crop of kohlrabi

Follow our steps for easy soil preparation

  • Kohlrabi does best in a neutral to slightly alkaline soil so adding lime before planting is beneficial and ensures good growth.
  • Dig in extra well-rotted organic matter such as compost, well-rotted manure and/or Seasol Super Compost to a depth of 30cm before planting.
  • A soil rich in nutrients helps build strong plants, so add Seasol Plant + Soil Booster (100g per square metre) and a fertiliser such as PowerFeed Controlled Release for Tomatoes & Vegetables.
  • Water in well and let the soil rest for a week or two.

Step 1 – Sowing seeds

  • Grow from seed sown directly into moist, well-prepared soil or seed raising mix such as Seasol Seed Raising & Cutting Potting Mix.
  • Sow at a depth of 6mm and space 15-20cm apart in rows 30-45cm apart.
  • Water in well with Seasol GOLD or Seasol (mix 30mL concentrate per 9 litres of water – standard watering can) as this will help to increase seed germination rates.
  • Soil should be moist but not wet, so check soil moisture daily to ensure kohlrabi seeds have the right conditions to germinate.

Note: These are not kohlrabi seeds, it’s an example of sowing seeds

Step 2 – Germination

  • Expect germination in 6-10 days (although it may be slower in very hot or cold conditions). Watch for the tiny leaves to come through the soil.
  • When kohlrabi sprout, they only have two leaves. These seedlings leaves look like two narrow leaves on either side of the stem.
  • Gently thin the tiny seedlings to 15-20cm apart when they are about 5cm high to reduce overcrowding and poor root development.
  • Water gently and apply Seasol GOLD or Seasol weekly for strong healthy root development and growth.

Step 3 – Baby kohlrabi seedlings

  • Transplant seedlings growing in cells or trays into small individual pots when they are big enough to handle. Allow them to grow on until they are ready to be planted out into the garden.
  • Keep young kohlrabi seedlings moist as inadequate watering can lead to poor bulb formation.
  • Protect emerging seedlings from snails and slugs who like to eat on the juicy, young foliage and destroy crops. (See ‘Things to watch out for’ below for more advice.)
  • Apply a liquid fertiliser such as PowerFeed PRO SERIES for Tomatoes & Vegetables for strong healthy growth in preparation for bulbs to develop as plants mature. Mix 20mL of concentrate per 9 litres of water (standard watering can).

Step 4 – Planting out kohlrabi seedlings

  • Transplant seedlings when they are around 7cm high spacing seedlings 20cm apart to allow for good stem formation.
  • If transplanting purchased seedling, plant in the same way as above, following the directions on the plant tag.
  • Push the soil firmly around the roots of the seedlings, but don’t push down from the top as this can compact the soil around the root zone stopping good root development.
  • Water your newly transplanted seedling in with Seasol GOLD or Seasol to aid plant establishment and strong healthy growth.

Step 5 – Kohlrabi plant growth

  • Keep the area around each plant hand weeded or hoed, as weeds compete for space, moisture and nutrients.
  • Water well and spread mulch around each plant to suppress weeds, help retain soil moisture and keep the root zone cool.
  • As you watch your kohlrabi grow over the following weeks you will see the green stem and leaf growth. The stem base starts to swell to form a bulb-like shape.
  • Every 6-8 weeks apply PowerFeed Controlled Release for Tomatoes & Vegetables to produce a bumper crop.
  • Apply by carefully mixing into the topsoil avoiding theplant stem and water it in thoroughly after application.

Step 6 – Kohlrabi bulb formation

  • The edible thickened stem (known as the bulb) form as the plant matures.
  • Check soil moisture and keep plants well watered for quick growth, strong bulb formation and the best flavour.
  • Apply liquid PowerFeed PRO SERIES for Tomatoes & Vegetables every week to fortnight for strong healthy bulb formation. Mix 50mL of concentrate per 9 litres of water (standard watering can).
  • Lack of nutrients or poor soil, can cause small bulbs and poor flavour. Adequate water and space are the other two key factors for a good harvest.

Step 7 – Kohlrabi harvest

  • Harvest kohlrabi as the stem begins to swell to golf ball size in about 8 to 12 weeks from planting. Leave some plants to form larger stem 5-7cm across.
  • The leaves can also be harvested when young and used like cabbage or kale (for example shredded or steamed).
  • Leaves are removed at harvest and the bulb can be stored for up to three weeks in the fridge.

Note: Kohlrabi that is heat or water stressed or over mature becomes tough, stringy and unpleasant to eat. Plants that are over mature for eating can be left to grow and flower to attract pollinators and beneficial insects to the vegetable patch and for seed.

Things to watch out for…….

  • Aphids These tiny black or green pests cluster under leaves. Squash, hose off or apply EarthCare White Oil insect spray to both side of the foliage.
  • Cabbage white butterflies The green caterpillars of this small white butterfly feed on all brassicas. Apply EarthCare Pest Oil insect spray to the foliage.  Erecting netted tunnels over the rows prevents this pest from laying eggs on the leaves of the crop.
  • Slugs and snails These pests can destroy young plants. Snails and slugs are active at night.  Remove these pests via hand or an organic method such as eggshells or coffee grounds around the plants.
  • Club root This is a fungal disease that affects growth and causes distorted swollen roots. Applying lime before planting reduces the likelihood of this disease. This is particularly important in acidic soils.
  • Downy mildew This fungus can attack leaves. Look for yellowing discolouration above and white mildew below the leaves. Remove affected leaves or apply EarthCare Rose Black Spot & insect spray to the foliage.

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