Growing exceptional cauliflower, cabbage, broccoli and Brussels sprouts

Top tips:

• Prepare soil well
• Choose a site with 6-8 hours of sun per day
• Water the soil well regularly
• Do not overcrowd.

Cauliflower, cabbage, broccoli and Brussels sprouts are members of the Brassica family. With good site selection, soil preparation and ample water throughout winter, they are easy to grow. Choosing the correct variety for your needs is important. Mini caulis and cabbages are ideal for a single person or couple, while larger varieties may suit families. If you want a continuous supply, select some early, mid-season and late maturing ones, or succession plant the one variety.

Colourful brassicas

Cauliflower comes in various colours including white, purple and green; cabbages come in white, green, red and purple; broccoli and Brussels sprouts are available in purple and green.

Planting time

Plant brassicas in April – May in Melbourne and keep well watered. Choose a site with full sun (6-8 hours a day). Some cabbage varieties can be planted in spring. Brussels sprout seedlings need to be raised in spring and planted out mid-summer so that they will be ready for harvest in autumn and winter.

Soil preparation

Dig the soil over roughly with a fork to open it up and aerate it. Add compost and well-rotted manure. Avoid fresh manure which is too high in nitrogen and will cause leaves to develop at the expense of heads. Add a handful of blood and bone per square metre for their nitrogen needs. If using the no-dig method, plant seedlings in deep pockets and add some compost to the bottom of the hole before planting.

pH

Soil pH needs to be 6.5 – 7.5, so test with a pH kit and if it is too acid add lime or dolomite a month before adding any well-rotted manure. Manure is more acidic and lime/dolomite is more alkaline, meaning they cancel each other out if applied at the same time. This means starting bed preparation about 5-6 weeks before planting.

Sowing seed

Prepare punnets by 3/4 filling them with seed-raising or potting mix and press this down firmly and water. Scatter the seeds onto this firmed bed. Add 6mm to 1 cm of mix, and then firm and water again. This stops the fine seed from washing through and out of the drainage holes. Keep moist at all times. Seedlings will emerge in about 7 days. Separate them at the 4-leaf stage and plant them in a seed tray with 20 to a tray. Plant out when they are 7-10cm in height.

Spacing

Brassicas need a lot of space, the larger caulis and cabbages can have a leaf span of 80cm. They are heavy feeders and require a lot of water. Spacing allows good air circulation which is vital in preventing disease. Plant large varieties 45-60cm apart and smaller varieties 30cm apart in rows 1 metre apart. Follow the instructions on the label or seed packet. Broccoli and Brussels sprouts should be planted 60-80cm apart.

Planting seedlings

Plant seedlings deeply i.e. bury them up to, and even over their lower leaves. This results in good root systems. Wobbly brassicas will not produce good heads. Most people do not plant them deeply enough: so be observant and if necessary, remove the plant, deepen the hole and plant again.

Net to protect, spray with Dipel and companion plant

All brassicas suffer enormous damage from the cabbage white butterfly which lays its eggs on the underside of the leaves. Green caterpillars emerge and strip the brassica leaves for food, killing the plant. There are 3 ways of dealing with caterpillars. First dip seedlings into Dipel (Yates Nature’s Way) which is an organic bacterium, toxic to caterpillars, just before planting. Secondly, plant American upland cress between plants. White cabbage butterflies will prefer this plant when laying eggs. It is also toxic to caterpillars. Thirdly, net to exclude white cabbage butterflies. If you do not net, you will need to spray every 7 days with Dipel, covering both the upper and underside of all leaves.

Foliar feed

Spray with Seasol or Maxicrop fortnightly. These are seaweed preparations that provide the plants with essential trace elements that may be deficient in the soil.

Watering

Brassicas require a lot of water. Small heads result from inadequate watering as do heads that are not firm. Rain is rarely adequate. Water twice weekly, deeply, throughout the winter. Place the hose beneath the leaves and flood directly onto the soil so that the roots receive sufficient water. Do not water the leaves. Dripline is an even better solution for getting adequate water to each plant. If the leaves of brassicas form a canopy over the soil (in the case of overcrowding) rainwater or overhead watering will not penetrate the soil.

Crop rotation

Brassicas develop root diseases such as club foot (a fungal disease) if continually grown in the same beds so choosing a new bed each year is essential.

Harvest

Use a sharp knife to cut through the stalk. Cauliflower and cabbage produce one head per plant, but broccoli produces side shoots that will grow into smaller heads. Cut the main head just above the side shoots and watch them develop. Sprouting varieties of broccoli will continue to produce. Harvest Brussels sprouts from the bottom of the stalk upward when sprouts are about 3cm in diameter. You can also eat brassica leaves.

Seed collection

Brassica seed cross-pollinates so it is not viable. Always buy commercial seed.

Specific hints for each Brassica

Cauliflower

Cauliflower season is April to August in temperate zones such as Melbourne.
White cauliflower heads will yellow if exposed to the sun. To prevent yellowing of cauliflower, fold a leaf over the cauliflower head. Don’t worry if the leaf snaps. Some varieties are self-blanching, meaning the leaves will grow over the ‘flower’. Damage to the terminal bud which turns into the head will cause failure. Fluctuating temperatures are the other enemy of healthy cauliflowers.

Cabbage

Cabbages love cool moist weather. In periods of high temperatures, protect cabbages from strong sun with shade cloth but remove it after the hot days have ended. High temperatures cause bolting. Keep well watered and water well before a heat wave. Lack of consistent water causes bolting and bitterness. Protect cabbages from snails and slugs with snail bait. Hose off any aphids and trap earwigs. Cabbage is easier to grow than cauliflower.

Broccoli

Broccoli comes in 2 forms: tight heads and sprouting. Remember that after cutting the main head, the side shoots will develop so keep watering and fertilising the plant. Purple-headed broccoli takes a very long time to produce heads, growing through winter and producing heads in spring. Broccoli can be planted in autumn and spring. If the florets begin to loosen, harvest straight away as they will begin to flower quickly. High temperatures and lack of consistent watering will result in poor yields. Generallybroccoli is very easy to grow. It’s best not to wash broccoli before storing. For insect protection see Cabbage above.

Brussels sprouts

These are tricky to grow and quite a gardening challenge. Seed needs to be planted in spring and seedlings planted out mid-summer. They take about 13 weeks after planting to mature and need cool summers and cold winters. (Cool summers can be difficult to come by these days in Melbourne.) Brussels sprouts are generally harvested in autumn-winter. Soil preparation, care and pest control are the same as other brassicas. What is unique is that as Brussels sprouts grow up a strong, straight stem, the leaves that are interspersed between the sprouts need to be removed, starting at the bottom and moving up as the sprouts get to about 2-3cm in diameter.

Written by Robin Gale-Baker