Radishes

Start from seed: January-March, August-December

Optimum soil temperature for germination: 8-30°C

Plant spacing: 2-5 cm

Days to maturity: 20-65 days

Introduction

Radishes (Raphanus sativus) are part of the Brassicaceae family, which also includes broccoli, cauliflower, kale, kohl rabi, Brussels sprouts, turnips, rocket, collards and mustard greens. These fast-growing root vegetables are one of the easiest and most rewarding crops for home gardeners, with many varieties maturing in as little as three to four weeks from sowing.

The radish has been cultivated for thousands of years, with evidence of its use dating back to ancient Egypt and China. The ancient Romans and Greeks also valued radishes for both culinary and medicinal purposes. The name “Raphanus” comes from Greek and means “quickly appearing,” referring to the rapid germination and growth of radish seedlings.

Radishes were introduced to Australia with European settlement and have since become a popular garden vegetable. They are an excellent crop for beginners and children, as their quick growth provides almost immediate gratification. Beyond their culinary uses in salads and as garnishes, radishes are also valuable as companion plants, helping to deter pests from other vegetables.

The radish plant forms a rosette of lobed leaves above ground, while below it develops the familiar crisp, pungent root in various shapes, sizes, and colours. While most are familiar with the small, round red varieties, radishes can also be long, cylindrical, or oval, with colours ranging from white to pink, purple, or black, depending on the variety.

Site and soil

Radishes are well-suited to Canberra’s climate and can be grown throughout the year, though they perform best during the cooler months of spring and autumn. In hot summer weather, they can become woody, pithy, and excessively spicy. Growth slows significantly during the coldest winter periods.

Choose a location that receives full sun for spring and autumn plantings. For summer plantings, a spot with afternoon shade will help prevent the roots from becoming too hot and spicy. Radishes are not fussy about location and can even thrive in pots, making them ideal for small gardens or balconies.

Soil preparation is important for good root development. Radishes prefer loose, well-draining soil that allows the roots to expand freely. Heavy clay soils should be amended with compost to improve drainage and texture. Aim for a soil pH between 6.0 and 7.0 for optimal growth.

For container growing, use pots at least 15 cm deep with drainage holes. Fill with a quality potting mix enriched with compost. Containers work well for radishes due to their shallow root systems and quick growing cycle.

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

Radishes are best grown from seed sown directly into the garden, because they don’t transplant well due to their quick growth and sensitive root systems. In Canberra, you can sow radish seeds year-round, however for best results sow seed from January to March and from August to December. Winter radishes, such as Daikon, grow more slowly, and are larger and denser than spring and summer radishes. They hold better in the soil without becoming bitter or woody. Winter radishes can be planted in February and March

Sow seeds in shallow drills about 1 cm deep and cover lightly with soil. Space rows 15-20 cm apart. For successive harvests, sow small batches every 7-14 days rather than planting a large area all at once. Keep the soil consistently moist until germination, which typically occurs within 3-7 days at optimal temperatures.

Once seedlings emerge and develop their first true leaves, thin them to 2-5 cm apart, depending on the variety. Smaller varieties need less space than larger winter radishes. The thinnings can be added to salads as microgreens if desired.

Radishes make excellent “marker plants” when sown alongside slower-germinating vegetables like carrots or parsnips. The quick-emerging radish seedlings will indicate the rows before the slower crops appear, and they’ll be harvested before the slower crops need the space.

Cultivation

Radishes require minimal care but consistent moisture for best quality. Water regularly to keep the soil evenly moist but not waterlogged. Irregular watering can cause the roots to split or become woody and overly pungent.

Fertilizing needs are modest, as too much soluble nitrogen promotes leaf growth at the expense of root development. If your soil was properly prepared before planting, additional fertilizer is unnecessary. A foliar spray early on 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.

Weed control is important, as radishes compete poorly with aggressive weeds. Hand weed carefully around the plants to avoid disturbing their shallow roots. A light mulch between rows can help suppress weeds and retain soil moisture, but keep it away from the plants themselves to prevent rot.

In Canberra’s climate, radishes grow best when temperatures are between 15-20°C. During hot weather, provide some shade to prevent bolting (premature flowering) and to keep the roots from becoming too pungent. In cooler weather, consider using row covers to extend the growing season.

Harvesting

Radishes are ready to harvest when the roots have reached the expected size for the variety, typically 2-5 cm in diameter for small round types. This can be as soon as 3-4 weeks after sowing for fast-maturing varieties, or 6-7 weeks for larger types. Check the days to maturity for the selected varieties.

Harvest promptly once radishes reach maturity, as they quickly become pithy, woody, and overly pungent if left in the ground too long. Pull the plants from the soil by grasping the tops firmly near the base of the leaves. If the soil is compacted, loosen it gently with a garden fork before harvesting to avoid breaking the roots.

After harvesting, trim the tops and roots, wash thoroughly, and store in the refrigerator. Fresh radishes will keep for about a week in the crisper drawer. For extended storage, they can be placed in a perforated plastic bag with a damp paper towel.

In addition to the roots, young radish leaves can be harvested and used in salads or as cooking greens. Some varieties, such as the ‘Rat-tail’ radish, are grown specifically for their edible seed pods rather than their roots.

Problems

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.

While radishes are generally trouble-free, they can face several challenges in Canberra gardens.

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.

Flea Beetles: Tiny beetles that create small holes in leaves, which can be especially damaging to young seedlings. Use floating row covers immediately after planting to prevent infestation, and apply diatomaceous earth around plants if beetles appear.

Root Maggots: The larvae of flies that tunnel into radish roots, causing damage and introducing rot. Practice crop rotation and use floating row covers to prevent adult flies from laying eggs near plants.

Bolting: Premature flowering due to stress, typically from heat or drought. Plant during cooler seasons and maintain consistent watering to prevent this issue.

Recommended Varieties

Several radish varieties perform well in Canberra’s climate:

Cherry Belle and Easter Egg: Both early-maturing (20-30 days) with smooth, round red roots and crisp white flesh. Excellent for spring and autumn plantings with good bolt resistance.

French Breakfast: An elongated radish with red skin and a white tip, maturing in approximately 23 days. Mild flavour and attractive appearance, ideal for salads.

White Icicle: Long, white radishes with mild flavour that remain tender even when mature. Best summer variety for Canberra, as it tolerates heat better than many others.

Sparkler: Round to oval radishes with bright scarlet skin and a white tip. Sweet, juicy flesh and fast maturation in about 25 days.

Watermelon (Red Meat): A larger winter radish with white skin and striking pink flesh. Sweet flavour, best grown in autumn for winter harvest.

Bravo: specialty daikon radish with purple skin and pale purple to white, crisp, sweet flesh that can be eaten fresh and used to make kimchi.

Black Spanish (Round or Long) e.g. Nero Tondo: Winter radishes with black skin and white flesh. More pungent flavour and excellent storage properties. Plant in late summer for autumn/winter harvest.

Daikon: Long white Japanese radishes with mild flavour, excellent for pickling. Best planted in late summer or autumn for winter harvest in Canberra.

For year-round production in Canberra, plant heat-tolerant varieties like White Icicle during warmer months and focus on quick-maturing varieties like Cherry Belle for spring and autumn. Reserve winter varieties like Black Spanish and Daikon for late summer and early autumn planting.

References

Active Vista. 2025. Radish Seed. http://activevista.com.au
Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
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.