Cauliflower

Start from seed: November-January (for Autumn and early Winter eating), March-April (for Spring eating)

Optimum soil temperature for germination: 7-30°C

Plant seedlings: December-January, March-April

Plant spacing: 40-50 cm

Days to maturity: 50-160 days

Introduction

Cauliflower, also known as Brassica oleracea var. botrytis, belongs to the Brassicaceae family, which also includes broccoli, cauliflower, kale, kohl rabi, Brussels sprouts, turnips, radish, rocket, collards and mustard greens.

Cauliflower originated from wild cabbage and was developed through selective breeding in the Mediterranean region. There are broadly two types: those forming curds in temperatures of 10-16⁰C and those that form curds at 20-25⁰C. The name “cauliflower” comes from Latin, meaning “cabbage flower.” This vegetable has been cultivated for more than 2,000 years, with early forms appearing in the Middle East before spreading to Europe in the 16th century.

The plants form compact heads, called curds, of unopened flower buds that can be white, purple, green, or orange depending on the variety. The typical white cauliflower requires blanching, achieved by being covered with leaves, to prevent the head from discolouring and tasting bitter. The plants have large, blue-green leaves that surround and protect the developing head.

Site and soil

Cauliflower can be challenging to grow in Canberra’s climate but will reward the patient gardener with delicious harvests if proper care is taken. Cauliflower requires a position with full sun (at least 6 hours daily) and protection from strong winds.

Prior to planting, prepare the soil by incorporating compost or aged manure and a balanced organic fertilizer. Cabbage prefers a fertile, well-drained soil with a pH between 6.0-6.5. It is commonly thought that they prefer alkaline soil. This is because clubroot disease can be problematic in acidic soils. If this is the case liming to raise the pH above 7.0, ideally to 7.8, is beneficial.

Avoid planting cauliflower in areas where other brassicas (cabbage, broccoli, kale) have been grown in the previous 3-4 years to reduce the risk of disease.

If growing in pots, use a large container (at least 30 cm deep) with high-quality potting mix enriched with organic matter and slow-release fertilizer.

For details on preparing soil and pots, including the use of lime, dolomite, gypsum and fertilizers, please refer to the COGS guide to garden bed preparation.

Planting Seeds and Seedlings

Cauliflower can be started from seed or purchased as seedlings. For seed sowing in Canberra, start seeds indoors or in a protected seedbed in February to April.

Seeds should be sown 6 mm deep in seed-raising mix and kept consistently moist but not wet. Seeds generally germinate in 4-10 days at temperatures between 18-24°C.

Once seedlings develop 2-3 true leaves (after about 4-6 weeks), they can be transplanted into the garden. To grow strong seedlings, it is best to hold your nerve and do not overwater or over feed. Ideally the roots should fill the cell trays or pots prior to planting out and seedlings should be a little hungry. Soft, sappy seedlings are prone to dying shortly after planting out.

Plant seedlings 40-50 cm apart to allow adequate space for the plants to develop. After planting, water thoroughly with a dilute seaweed solution to reduce transplant shock.

Apply organic mulch around plants to help retain soil moisture, suppress weeds, and regulate soil temperature.

Cultivation

Cauliflower requires consistent care throughout its growing cycle to produce good heads. The soil should remain consistently moist but not waterlogged. Irregular watering can lead to poor head formation or bitter taste.

Cauliflower is a heavy feeder and benefits from side dressing with a balanced organic fertilizer half way through the growing season. Avoid high-nitrogen fertilizers, which can cause leafy growth at the expense of head development. A monthly foliar spray with seaweed solution; a mix of worm juice, seaweed and compost tea; or trace elements will help boost growth and resilience to pests and diseases. Cauliflower is prone to molybdenum deficiency which will result whiptail manifesting as malformed, yellow leaves, twisted plants and undeveloped heads.

The curds are surrounded by the leaves which block the sun. Exposure to the sun will result in discoloured and bitter curds. Therefore, if the leaves are not naturally covering the curds once the head is about 5-8 cm in diameter, gently fold the outer leaves over the head. Check regularly to monitor growth and ensure adequate ventilation.

Cauliflower is sensitive to temperature fluctuations. Extended periods below 10°C can cause premature heading (buttoning), while temperatures above 26°C can cause loose, discoloured heads. In Canberra’s climate, timing is crucial to avoid summer heat and winter frosts.

If light frosts are expected, protect young plants with cloches, frost cloth, or upturned buckets overnight.

Regular weeding is necessary, especially when plants are young, to prevent competition for nutrients and water.

Harvesting

Cauliflower heads should be harvested when they reach full size but before the curds begin to separate. Depending on the variety and growing conditions, this is typically 70-100 days after planting.

A mature cauliflower head should be firm, compact, and approximately 15-20 cm in diameter. The earlier you harvest, the more tender the cauliflower will be.

To harvest, cut the stem about 2-3 cm below the head using a sharp knife. Some varieties may produce side shoots after the main head is harvested, although these will be smaller than the primary head. This can be encouraged by using a knife to cut a cross in the stem where the head was removed.

For best flavour and texture, consume fresh cauliflower as soon as possible after harvesting.

Problems

There are numerous pests and diseases that can affect cauliflower. The best approach is to have a reliable Australian reference book to identify problems. Garden Pests, Disease and Good Bugs by Denis Crawford is recommended.

A general strategy to follow with any problem is to observe the plant carefully before taking action. Identify the problem then carefully consider the course of action. For example, with pest insects, you often can see a predator nearby. If you watch and wait the predator may deal with the problem for you. Beneficial predatory insects which feed on pest insects can be purchased from suppliers such as Bugs for Bugs. If the problem needs further action the above recommended book has suggestions.

Practicing good garden hygiene, crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention.

There are several pests and diseases that can affect cauliflower in Canberra.

Cabbage White Butterfly (Pieris rapae): This common pest lays tiny white eggs on the undersides of leaves. The green caterpillars that hatch are perfectly camouflaged and feed on leaves, creating irregular holes and contaminating plants with their droppings. Exclusion netting is the most reliable method to prevent damage from cabbage white butterfly. Keep in mind that the netting also excludes beneficial insects and birds that glean plants cleaning up other pests. Thus, leaving the netting on for too long can result in populations of sap suckers such as aphids, thrips and white fly building up inside the netting.

Control methods include:

Covering plants with fine insect mesh or exclusion netting from the time of planting
Regularly inspecting and manually removing eggs and caterpillars
Using biological controls such as Bacillus thuringiensis (also known as Bt and sold as Dipel) for significant infestations
Creating butterfly decoys by placing white plastic pieces around plants
Avoiding brassica weeds that act as hosts

Clubroot (Plasmodiophora brassicae): This soil-borne disease causes swollen, deformed roots and stunted growth. Plants may wilt during warm weather and show yellowing leaves. The disease thrives in acidic soils (below pH 7.0) and can persist in soil for many years. Management includes:

Maintaining soil pH above 7.0, ideally 7.8, through liming
Practicing crop rotation (avoid planting brassicas in the same area for at least 4 years)
Improving drainage in wet areas
Removing and disposing of infected plants (do not compost)
Using disease-free transplants and clean tools

Aphids, thrips and white fly: These small sap-sucking insects can transmit celery mosaic virus. They often cluster on the undersides of leaves, causing distortion and stunting. Small populations can be controlled by washing them off with a strong stream of water or using insecticidal soap. Alternatively, neem oil or pyrethrin can be used. Beneficial predators like ladybugs and lacewings should be encouraged and can be purchased for release on the crop. Look for aphid mummies which are evidence that the aphid has been parasitised. Eggs can also be parasitised and will appear bronze in colour. Generally speaking, plants that are high in soluble nitrogen (nitrates and ammonia) are prone to attack by sap sucking insects. Ideally avoid using soluble nitrogen fertilisers and ensure plants have adequate trace elements. This can be achieved by using foliar sprays.

Whiptail is the result of Molybdenum deficiency. Since Molybdenum is vital for plants to utilise nitrogen plants initially develop symptoms of nitrogen deficiency – pale and stunted leaves. Later the outer leaves become yellow and the margins die causing the leaves to become narrower and distorted. In severe cases the plant leaves resemble twisted straps, hence the name Whiptail. The problem is more likely to occur in acidic soils below 6.5. Increasing the pH above this will increase availability of Molybdenum perhaps preventing the disorder. Foliar sprays can correct the problem if applied early enough. After the onset of whiptail foliar sprays will not be effective. Although only small amounts of Molybdenum are required, seed saved from soil deficient in molybdenum will most likely produce plants with Whiptail.

Recommended Varieties

Several cauliflower varieties perform well in Canberra’s climate.

All Year Round: A reliable heirloom variety with medium-sized, firm white heads. Good for Canberra’s conditions as it’s adaptable to different planting times.
Snowball: early large white heads usually ready 65 days after transplant
Paleface: developed in Western Australia but was grown in cooler parts of Victoria
Selection 174 (also known as ‘Quickheart’): An Australian-bred variety producing medium-sized, heavy white heads that are well-protected by inner leaves. 90-100 days to maturity.
Purple Sicilian: A striking purple variety with good cold tolerance and slightly sweeter flavour than white types. The purple colour comes from anthocyanins (beneficial antioxidants).
Romanesco: Distinctive lime-green heads with spiral-formed curds. Requires consistent growing conditions but offers excellent flavour and visual appeal.
Vitaverde: lime green Romanesco style
Puntoverde: yellowish-green Romanesco style
Mini Cauliflower: Compact varieties suitable for small gardens or containers. These typically mature faster (60-70 days) than standard varieties.

When selecting varieties, consider those with mentioned disease resistance, particularly to clubroot if this has been a problem in your garden previously.

References

Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
Department of Primary Industries and Regional Development. (n.d.). Managing clubroot in vegetable brassica crops. https://www.agric.wa.gov.au/broccoli/managing-clubroot-vegetable-brassica-crops
Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023.
Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.
Western Australian Department of Primary Industries and Regional Development. Diseases of vegetable brassicas [Internet]. 2023. Available from: https://www.agric.wa.gov.au/broccoli/diseases-vegetable-brassicas
Yates Australia. How to Grow Cauliflower [Internet]. 2024. Available from: https://www.yates.com.au/how-to-grow/cauliflower/