Celeriac

Start from seed: August-September

Optimum soil temperature for germination: 21-24°C

Plant seedlings: November-December

Plant spacing: 30-40 cm

Days to maturity: 100-120 days

Introduction

Celeriac (Apium graveolens var. rapaceum), also known as celery root or knob celery, belongs to the Apiaceae family, which also includes carrots, parsley, and fennel.

Celeriac was selected from celery 400 years ago in Europe. It is a variety of celery grown for its large, bulbous swollen stem rather than its stalks. The round swollen knobbly stem, often referred to as a root is immediately beneath the leaves and sits half in and half out of the soil. The brownish skin conceals crisp, white flesh with a delicate celery-like flavour. Above ground, celeriac produces dark green, celery-like foliage on short stems that is usually discarded due to the bitter flavour.

Despite its somewhat unattractive appearance, celeriac is a versatile vegetable with a mild, nutty flavour that combines elements of celery and parsley with a creamy, potato-like texture. It’s a valuable cool-season crop that stores well through winter.

Site and soil

Celeriac can be successfully grown in Canberra’s cool climate with proper timing and care. It prefers partial shade in Canberra’s hot summer, ideally receiving 3-6 hours of sunlight daily. Choose a location that offers some protection from intense afternoon sun.

Prior to planting, enrich the soil with plenty of organic matter. Celeriac thrives in well-drained, moist soil with a pH between 6.0-7.0. The addition of aged compost or well-rotted manure and complete organic fertiliser will improve soil structure and provide nutrients for this heavy-feeding crop.

If growing in containers, use a high-quality potting mix enriched with organic fertilizer. A container with a minimum capacity of 20 litres is recommended for each celeriac plant to accommodate its extensive root system.

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

Celeriac seeds are extremely small and can be slow to germinate. For best results, start seeds indoors in August to September. Seeds can be sown in cell trays, seed trays or small pots filled with good quality seed-raising mix.

If direct sowing, the tiny seeds should be sprinkled lightly on the surface of moist soil and covered with only a very fine layer of soil or vermiculite, as they require light for germination. Keep the soil consistently moist but not waterlogged.

Germination can be slow and erratic, typically taking 14-21 days when soil temperature is between 20-24°C. To improve germination rates, some gardeners recommend soaking the seeds overnight before sowing or germinating them on moist paper towels in a zip-lock bag until roots appear.

Once seedlings develop 2-3 true leaves, transplant them into individual pots to grow on until they’re ready for the garden. They are so sensitive that it is advised to transplant one seedling at a time so as not to let the roots dry out. Seedlings should be about 10cm tall before planting out, which is usually in November to December in Canberra, after the risk of frost has passed.

When transplanting to the garden be careful not to let the roots dry out. Space plants 15-20cm apart in rows 25-30cm apart. Spacing will depend on the desired harvest size. Water thoroughly after planting and apply liquid seaweed to reduce transplant shock. Mulch around the plants with organic matter to retain moisture and suppress weeds.

Cultivation

Celeriac is a long-season crop requiring consistent care over several months. After transplanting, the focus should be on maintaining even soil moisture, as drought stress can lead to woodiness and a bitter taste

In Canberra’s climate, regular deep watering is essential, especially during summer. Water deeply rather than providing frequent shallow irrigation. Consistent moisture is critical for root development, but avoid waterlogging, which can cause rot.

Celeriac is a heavy feeder and benefits from a side dressing of complete organic fertiliser and or compost midway through the growing season. 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.

As the plants develop, remove any side shoots to encourage the main stem to grow larger. Throughout the season, remove older, outer leaves as they begin to yellow, but leave enough foliage for the plant to continue photosynthesizing effectively.

Celeriac growth follows an interesting pattern: for much of the season, you’ll see mainly top growth with little apparent stem development. Then, in late summer and early autumn, the stem beneath the leaves suddenly begins to swell rapidly. Be patient during the early growth phase, as the plant is establishing itself before putting energy into the swollen stem.

To blanch the stem and reduce bitterness, some gardeners remove lower leaves and mound soil around the developing bulb. However, this is optional and primarily affects appearance rather than flavour.

Harvesting

Celeriac is typically ready for harvest about 100-120 days after transplanting, generally from autumn through early winter. Harvest time is flexible, as celeriac stores well in the ground even after light frosts, which can actually improve flavour

They can be harvested once they reach 10-14cm in diameter, though smaller stems (about tennis ball size) tend to be tastier and tender. To harvest, carefully dig around the swollen stem with a garden fork, loosening the soil before lifting the plant. Cut off the foliage, leaving about 2-3cm of leaf stems attached to the root.

Celeriac can be stored with soil still attached in a cool, dark, well-ventilated place such as a garage or cellar. Alternatively, clean off the soil, trim the small roots, and store in perforated plastic bags in the refrigerator, where they’ll keep for several weeks.

For longer storage, celeriac can be placed in boxes filled with slightly damp sand in a cool location (around 0-5°C), where they can last for up to 4-6 months.

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.

Celeriac can face certain challenges during its growth. Here are some common issues in Canberra’s growing conditions:

Slugs and snails: These are major pests for young celeriac seedlings in Canberra. Use organic slug baits (iron EDTA), copper tape, or beer traps to control populations. Regularly checking plants in the evening when slugs are active can help catch them before they cause significant damage.
Aphids: 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.
Bolting: Exposure to cold temperatures when plants are young can trigger premature flowering (bolting). Ensure seedlings are protected from cold and transplant at the appropriate time when soil has warmed sufficiently. Drought stress can also trigger bolting so ensure soil is moist.
Cutworm: are the larvae of several species of moths. Their name comes from their habit of cutting off seedlings at ground level. Prevent by removing weeds around seedlings and protecting seedlings with sleeves made from cardboard or cut off drink bottles. Natural predators include lacewing larvae, ladybirds, parasitic wasps and birds.

Practice four-year crop rotation, avoiding planting celeriac where other crops in the Apiaceae family (celery, carrots, parsnips) have recently grown to prevent soil-borne diseases and pests.

Recommended Varieties

Several celeriac varieties perform well in Canberra’s cool climate. When selecting varieties, consider those with shorter maturity times and good disease resistance.

Giant Prague: An heirloom variety dating back to 1871, producing large roots with strong celery flavour. It remains popular for its reliability in cool climates.
White Alabaster: This variety produces smooth, white roots that are less likely to discolour during cooking. It has excellent storage qualities and a refined taste.
Balena F1: Hybrid early celeriac with strong bolting tolerance. Roots have a dense creamy interior. Excellent upright leaf growth and healthy foliage. Interiors are a lovely solid white, with little pithiness. Quick to mature with exceptional cold tolerance.
Verona: Originally from Northern Italy and named after the city of Verona, this heirloom celeriac variety produces large, white skinned knobbly, stems with a sweet yet savoury celery-type flavour.
Monarch: Features a smoother skin than many varieties, making it easier to clean and prepare. It has good disease resistance and a mild, pleasant flavour.

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.
Johnny’s Selected Seeds. Celery & Celeriac Seeds [Internet]. USA: Johnny’s Selected Seeds; 2024 [cited 2025 May 6]. Available from: https://www.johnnyseeds.com/vegetables/celery-and-celeriac/
Royal Horticultural Society. How to grow Celeriac [Internet]. United Kingdom: RHS; 2024 [cited 2025 May 6]. Available from: https://www.rhs.org.uk/vegetables/celeriac/grow-your-own
Succeed Heirlooms Australia. Celeriac ‘Giant of Prague’ Seeds [Internet]. Australia: Succeed Heirlooms; 2024 [cited 2025 May 6]. Available from: https://www.succeedheirlooms.com.au/heirloom-vegetable-seed/heirloom-celery-celeriac-seeds/celeriac-giant-of-prague.html