Celeriac: growing, harvesting and uses

Celeriac is a rewarding and delicious vegetable to grow at home. It is closely related to celery but is grown for its swollen root. Plus, celeriac is hardier and more disease resistant than celery.

Celeriac (Apium graveolens var. rapaceum) is not just a vegetable for soups, it can also be used in many other ways. Read on to find out all about celeriac, including how to grow, harvest, as well as use and preserve this flavoursome vegetable.

Celeriac: origins & properties

Celeriac, also known as knob celery, celery root or turnip-rooted celery, has been a staple winter vegetable since it was introduced to the UK in the 18th century. It is a variety of celery (Apium graveolens) cultivated for its bulbous, edible hypocotyl. The plant is at home in the temperate latitudes of the northern hemisphere.

Celeriac reaches a height of 60cm and forms its swollen storage organ in a part of the lower stem called the hypocotyl, in between the foliage and the roots. Once mature, the storage organ, or tuber, can weigh between 200g and 2kg, depending on the variety and other environmental influences. On average, the celeriac tuber weighs 650g and measures 10cm in diameter. A healthy celeriac plant has bright green leaves that are pinnate.

Celeriac is a biennial plant in the wild. However, like many root vegetables, celeriac is grown as an annual. It is harvested at the end of its first growing season, when the flavour and quality of the tuber are at their peak. If you want your celeriac plant to produce seeds, you need to leave it in the ground over winter and wait for it to flower in the second year of growth. Celeriac, like other members of the Apiaceae family, produces flowers that are white disc-shaped umbels. The nectar-rich flowers bloom from July to September. After pollination, each flower produces two small, flat seeds in a five-ribbed split fruit. The celeriac seeds ripen in September.

The best celeriac varieties to grow

When looking for the right celeriac seeds, it is hard to know which to choose from more than a dozen celeriac varieties. These varieties differ not only in taste but also in tuber size and resistance to disease or bolting. Here are some of our favourite celeriac varieties for growing at home:

• ‘Ibis’: delicate celery flavour; fast growing, large and smooth tuber; bolt-resistant; resistant to celery leaf spot (Septoria apiicola).
• ‘Giant Prague’:an heirloom variety; slight celery and aniseed flavour; stores well; harvest when roots are 8-10cm in diameter.
• ‘Mars’: intense, slightly nutty flavour; stores well; thick, green-white, fleshy tubers; resistant to celery leaf spot.
• ‘Monarch’: subtle nutty flavour; extremely large, creamy-coloured tuber; resistant to celery rust (Puccinia apii).
• ‘Prinz’: strong celery-like flavour; bolt-resistant; suitable for greenhouses; white, firm flesh; resistant to celery rust.

Growing celeriac

Growing celeriac from seed is not difficult, but it does require a little patience. Celeriac thrives in a sunny spot in a vegetable bed, raised bed or cold frame. It likes deep, moist, nutrient-rich soil.

Celeriac takes a long time to mature, so it is important to start the seeds off early in spring. In early March, sow the celeriac seeds in pots filled with sowing soil, such as our Plantura Organic Herb & Seedling Compost. Lightly press the celeriac seeds into the soil but do not cover with soil, as they require light to germinate. Water well and regularly, as celeriac like a moist environment. Cover with a clear plastic bag and air daily. Place in a bright place that is around 18 – 20 °C, ensuring the temperature does not drop below 15 °C. The seedlings will start to germinate after around 14 days, but germination may happen sporadically. Once the celeriac seedlings are 10 to 15cm tall, they are ready to be transplanted outside if it is warm enough. Wait until mid-May, or after the last frost, before planting outdoors. Plant them outside by the end of June at the latest.

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It is important to prepare the bed to create the best starting conditions for your young celeriac plants. Loosen the soil and remove any weeds and stones. Work manure or manure-based compost into the soil to give the soil more nutrients. Plant in rows, spacing the celeriac plants 40cm apart. A row and plant spacing of 40cm ensures each plant has enough space to develop. Keep the soil consistently moist. Add a layer of garden compost to the soil around the celeriac plants to help retain moisture.

Tip: stick to a 4-year crop rotation with celeriac. Celeriac requires a lot of nutrients to grow, so it is important to consider what crops you want to plant in the bed for the next 3 to 4 years following your celeriac harvest. Avoid other umbelliferous plants (Apiaceae), such as carrots (Daucus carota subsp. sativus) or parsley (Petroselinum crispum ssp. crispum) because they require many of the same nutrients and the soil will be depleted of these. Plants in the same family are also susceptible to many of the same pests and diseases. Excellent choices for succession plants include kohlrabi (Brassica oleracea var. gongylodes), cauliflower (Brassica oleracea var. botrytis), Brussel sprouts (Brassica oleracea var. gemmifera), leek (Allium porrum), sweetcorn (Zea mays) and beetroot (Beta vulgaris subsp. vulgaris var. conditiva).

Celeriac companion plants

Here are some good companion plants to grow beside celeriac:

• Leek
• Beans (Phaseolus vulgaris)
• Spinach (Spinacia oleracea)
• Tomatoes (Solanum lycopersicum)
• Cucumbers (Cucumis sativus)
• Cauliflower
• Kohlrabi
• Other brassicas

Do not plant these alongside celeriac:

• Potato (Solanum tuberosum)
• Lettuce (Lactuca sativa var. capitata)
• Peppers (Capsicum spp.)
• Parsley
• Parsnip (Pastinaca sativa)
• Carrots

Care tips

It is important to water celeriac plants sufficiently. Keep the soil moist but avoid waterlogging, since waterlogged soil will encourage root fungi. As the young plants tend to bolt, cover with horticultural fleece if temperatures drop below 10 °C. This is especially important for older varieties – newer varieties are usually more resistant to bolting. Hoe occasionally between the plants throughout the growing season to combat weeds.

Fertilising celeriac during the growing period will help increase yields due to its high nutrient requirements. Celeriac has a particularly high demand for potassium and nitrogen, so a potassium rich fertiliser, such as our Plantura Tomato Food, is an excellent choice. Our fertiliser has a long-term effect of 3 months. Besides this, from June onwards, an occasional watering with liquid plant manure will help boost potassium and nitrogen, promoting tuber growth. Liquid manure also contains boron which helps to prevent celery heart rot.

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As the celeriac matures and the tuber grows to the size of a walnut, keep the area around the base of the plant, or the upper tuber, clear of soil, side shoots and fallen leaves. This will allow the tuber to grow well.

Celeriac can be susceptible to pests, such as celery fly (Euleia heracleid). Use horticultural fleece to help protect your crops from such infestations. Voles are also a common pest of celeriac. Use barriers around your crops to help limit damage from voles or other rodents.

To produce celeriac seeds yourself for propagation or consumption, it is necessary to overwinter the celeriac. Celeriac is frost tolerant, and so you can leave it in the ground during winter and cover the soil with brushwood, straw or fleece to provide insulation.

Harvesting celeriac

Celeriac can be harvested from late August, however, it is best to wait until October, as the flavour of the vegetable will develop with time. Pull the stems to carefully ease the plant out of the soil; use a fork if necessary. To prepare for storage, shorten the roots and twist off the leaves. To increase its shelf life, celeriac can be stored in moist sand in a frost-free cellar. Only wash the celeriac right before you plan to use it.

Can you freeze celeriac?

In the fridge, celeriac will keep for up to 14 days. However, freezing celeriac will extend its shelf life even further. Here are the simple steps for how to freeze celeriac:

1. Cut off the leaf base and root remnants.
2. Peel the celeriac with a sharp knife.
3. Cut according to later use: e.g. into cubes for celeriac mash or soup and into larger slices for roasted celeriac.
4. Place in freezer bags, press out any air and seal airtight.
5. Store in the freezer until ready to use.

Pickled celeriac is another great celeriac recipe:

1. Cut into matchstick-size strips and place in clean pickling jars with some peppercorns and thyme.
2. In a saucepan, combine equal parts apple cider vinegar and water, as well as some honey or sugar, lemon juice and salt.
3. Bring to a simmer, then pour over the raw celeriac jars.
4. Allow to cool before sealing the jars.

Uses

Celeriac is a flavoursome and versatile vegetable. It has tough skin, so always peel it. In many dishes, celeriac can be used to substitute potato or root vegetables. For example, mashed celeriac and roasted celeriac make excellent side dishes. Like celery (Apium graveolens var. dulce), celeriac can also be eaten raw. Celeriac salads are easy to make, simply slice it thinly and pair with some complementary ingredients like apples and walnuts and top with a nice vinaigrette.

Health benefits

Celeriac is incredibly nutritious. It provides the body with zinc, iron, potassium, sodium, phosphorus, vitamin C, numerous B-group vitamins and carotenoids. It is also said to be an antioxidant and anti-inflammatory, as well as aid in digestion.