Swedes

Start from seed: February

Optimum soil temperature for germination: 7-25°C

Plant spacing: 15-20 cm

Days to maturity: 70-120 days

Introduction

Swede (Brassica napus var. napobrassica), also known as rutabaga in North America, is a root vegetable belonging to the Brassicaceae family which also includes cabbage, broccoli, cauliflower, kale, kohl rabi, Brussels sprouts, turnips, radish, rocket, collards and mustard greens. The swede is actually a naturally occurring hybrid between cabbage (Brassica oleracea) and turnip (Brassica rapa).

Originating in Scandinavia in the 17th century, swedes were first documented growing wild in Sweden by Swiss botanist Gaspard Bauhin in 1620, which explains their common name. They were initially grown as animal fodder but gradually gained popularity as a staple food crop, particularly in cooler northern regions.

Swedes develop large, round roots with purple tops and creamy yellow flesh. They have a sweet, earthy flavour that intensifies after exposure to frost. The leaves grow in a rosette pattern and resemble those of turnips but are more blue-green in colour.

Swedes grow particularly well in Canberra and can be an excellent addition to the winter vegetable garden due to their cold hardiness and excellent storage capabilities.

Site and soil

Swedes prefer full sun but will tolerate partial shade. Choose a position that receives at least 6 hours of sunlight daily. Swedes grow best in cooler weather, and are best planted in late summer for winter harvest.

The soil should be deep, well-drained, and rich in organic matter. Swedes prefer a slightly acidic to neutral pH of 6.0-6.8. Avoid acidic soils with a pH below 5.5, as this can lead to reduced growth and increased susceptibility to club root disease.

Before planting, prepare the soil by digging in well-rotted compost or aged manure and a complete organic fertiliser to improve fertility and structure. Swedes are moderate to heavy feeders, so incorporating a balanced organic fertiliser during soil preparation is beneficial.

Swedes grow well following legumes, such as beans or peas have been grown the previous season, due to the fixed nitrogen.

If growing in containers, choose deep pots at least 30-40 cm in depth to accommodate the developing roots, and use a good quality potting mix enriched with compost.

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

Planting Seeds and Seedlings

In Canberra, swedes are best sown in February for a winter harvest. Seeds should be sown directly into the garden bed because they don’t transplant well due to their taproot.

Sow seeds at a depth twice the size of the seed, spaced 5 cm apart in rows 25-30 cm apart. Once seedlings reach about 5 cm in height, thin them to 15-20 cm apart to allow sufficient space for the roots to develop. If sown too densely, the roots will be small and misshapen.

Swedes germinate best when soil temperatures are between 7-25°C, with germination typically occurring within 7-10 days. Cooler soil temperatures may delay germination, and temperatures above 25°C can reduce germination rates.

After sowing, keep the soil consistently moist but not waterlogged. A layer of fine mulch can help retain soil moisture and prevent weed growth. Once seedlings are established, mulch around plants with straw or other organic material.

Cultivation

Swedes are relatively undemanding once established but require consistent watering, especially during root development and dry periods. Aim for about 25mm of water per week, either from rainfall or irrigation.

Regular weeding is important, particularly when plants are young, as swedes don’t compete well with weeds. Be careful not to damage the developing roots when removing weeds.

The aim in planting in February, is to have plants well established in early to mid-Autumn to enable the photosynthetic parts of the plant to transport starches to the root. Swedes are highly frost-tolerant.

Swedes don’t require additional fertiliser if the soil was well prepared before planting. However, if growth seems slow, a side dressing of balanced organic fertilizer midway through the growing season can be beneficial. 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.

The flavour of swedes actually improves after frost because the cold temperatures stimulate the conversion of starches to sugars, making the roots sweeter.

As the roots mature, you may see them push up partially above the soil surface. This is normal and doesn’t require hilling or covering, unlike potatoes.

Harvesting

Swedes are typically ready to harvest 70-120 days after sowing, depending on the variety and growing conditions. They can be harvested when the roots reach the size of a tennis ball (about 7-10 cm in diameter), though they can grow much larger.

For the sweetest flavour, harvest swedes after they’ve been exposed to a few frosts.

To harvest, loosen the soil around the plant with a garden fork and then carefully lift the root. Twist off the foliage, leaving about 2 cm of stem on the root to prevent rotting during storage.

In Canberra, Swedes can be left in the ground and harvested as needed throughout winter. The cold soil serves as nature’s refrigerator. However, they should be harvested before spring when increasing daylength and warmer temperatures will cause them to become bolt and become woody.

For storage, brush off excess soil (don’t wash until ready to use) and store in a cool, dark place with good air circulation. Under ideal conditions, swedes can store for 4-6 months. They can also be peeled, chopped, and blanched for freezing.

Young swede greens can also be harvested sparingly and used like turnip greens or kale in cooking.

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.

Several pests and diseases can affect swedes 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.

Flea beetles are small black beetles that jump when disturbed and create small holes in the leaves, particularly damaging to young seedlings. Floating row covers from sowing until plants are established can help prevent infestations. Diatomaceous earth sprinkled around plants can also be effective.

Practicing crop rotation is essential for preventing the buildup of pests and diseases. Avoid planting swedes or other brassicas in the same location for at least 3-4 years.

Recommended Varieties

Several swede varieties perform well in Canberra’s climate:

Laurentian: The most widely grown variety in Australia with purple tops and yellow flesh. Produces uniform, globe-shaped roots with sweet, fine-grained flesh. Good storage capabilities and matures in about 90-100 days.
Helenor: An excellent variety that develops good colour early in root development. Produces round, uniform roots with light orange flesh and a sweet flavour. High-yielding and stores well, maturing in approximately 90 days.
American Purple Top: Similar to Laurentian with purple tops and yellow flesh. Reliable producer with good disease resistance and excellent flavour. Matures in 90-100 days.
Wilhelmsburger: A German heirloom variety with green tops and golden flesh. Known for its excellent flavour and good storage qualities. Matures in approximately 100-110 days.

References

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.
Yates Australia. How to Grow Swede [Internet]. 2024 [cited 2025 May 6]. Available from: https://www.yates.com.au/how-to-grow/swede/