Turnips are a fairly easy and reliable crop to grow in your polytunnel. If you choose the correct varieties, you can be growing turnips almost all year round. A polytunnel can be useful for protecting your crop in early spring and in the depths of winter, meaning that you can keep turnips in the ground.
The turnip, scientifically known as Brassica rapa variety rapa, is a robust biennial plant belonging to the mustard family (Brassicaceae). It is grown primarily for its succulent roots and delicate, edible greens.
There are early and maincrop varieties of turnips to choose from. Early turnips can be pulled small, when they are around golf-ball sized if you want to eat them raw, around the size of a tennis ball if you want to cook with them. Larger, maincrop varieties can be pulled from October onwards. Turnip greens also offer a bonus crop, in addition to the roots.
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Turnips grow best in full sun, in a moist yet free-draining soil or growing medium that is rich in organic matter. This is a crop that generally prefers cooler conditions and so can do best in the shoulder seasons rather than during the height of summer.
To grow turnips at home you will require:
Turnip seeds
Garden space or containers
Well-draining soil with good fertility
Full sun to partial shade
pH tester or soil test kit (optimal pH range: 6.0 to 7.5)
Watering can or hose
Organic Mulch (to retain moisture and suppress weeds)
Fertilizer (balanced or high in phosphorus and potassium)
Hand trowel or shovel for planting
Row covers or netting (to protect against pests)
Gardening gloves
Pruning shears or scissors (for thinning seedlings)
Harvesting knife or trowel.
Growing good turnips starts with good soil. Look to the soil and you cannot go too far wrong. Turnips are relatively easy to grow from seed.
Turnips need a fertile soil, as mentioned above. So to make sure your growing area is suitable you should dig in or top-dress with plenty of organic matter to prepare the area for planting.
Sow early varieties of turnip between March and June and maincrop varieties between Mid July and Mid August.
Early varieties will take only around six - eight weeks to reach an edible size for salads and so can be planted as a catch crop to take advantage of space left by a slower growing crop.They will take only around six - eight weeks to reach an edible size for salads.
Early turnips will be up and away before the space and nutrients are needed by the other crop. Early turnips also work well for successional sowings, so you can enjoy a few turnips at a time rather than getting a glut.
The usual strategy is to sow turnips thinly where they are to grow. Thin out the seedlings until they are around 15cm apart for early varieties, or double that for your maincrop turnips.
If you have limited ground space or prefer smaller turnips, you can plant turnip seeds in containers outdoors, preferably in a warm, sunny location
Select a container with a width of at least 40cm (16in) and fill it with multi-purpose compost, ensuring it is well-draining. Water the compost thoroughly.
Scatter the turnip seeds thinly across the surface of the compost, then cover them with approximately 2cm of additional compost.
Water the container regularly to keep the compost consistently moist but not waterlogged.
Once the turnip seeds germinate and seedlings appear, thin them out if necessary, leaving approximately 10cm of space between each seedling.
To achieve earlier harvests, consider starting hardy turnip varieties indoors during late winter: Fill a modular tray with seed compost, ensuring it is well-watered. Create a hole approximately 2cm deep in each module of the tray.
Place two seeds into each hole, then cover them with additional compost. If multiple seeds germinate in a single module, remove the weaker seedling. Alternatively, sow up to four seeds together in a small clump per module for harvesting as mini-vegetables. In this case, avoid thinning out the seedlings.
From early March, gradually acclimate the young plants to outdoor conditions over a period of two weeks through a process known as hardening off. Following the hardening off period, plant the seedlings into prepared ground with minimal root disturbance.
Space them approximately 15–23cm (6–9in) apart. If sown as a clump, transfer each whole module into the ground without splitting the seedlings. Water the newly transplanted seedlings thoroughly and continue regular watering to ensure that they grow as they should.
Turnips, classified as hardy biennials, are typically grown as annuals despite their natural two-year lifecycle. In their second year, they naturally flower and produce seeds. However, in the first year, turnips may occasionally bolt, prematurely flowering and seeding. This bolting can occur due to stress induced by extreme temperatures (both cold and hot), insufficient nutrients, or inadequate water supply. Such stressors may also lead to stunted root growth, the formation of aerial roots, or the development of greens without significant root growth.
To prevent bolting, it's advisable to harvest turnips before temperatures rise above 27°C. This helps avoid premature flowering.
Turnips will need a cool, moisture retentive soil in order to thrive. In your polytunnel, you may find that turnips will do better when shaded in summer by a taller companion plant.
Watering is a key concern and you should always be sure to water well, especially in hot weather. Mulch will also help turnip roots to hang onto the water they need. If they dry out or overheat, turnips can be prone to going to seed.
As soon as the turnip seedlings are around 12cm or so high, apply a rich organic mulch of well-rotted organic matter, compost or leaf mould to a depth of around 5cm.
An organic mulch will also help to reduce weed growth, but where weeds emerge, remove these promptly if they are introducing too much competition and affecting turnip growth.
If you have sown early turnips in succession then you can expect to harvest early turnips from May right through to September. Simply pull the turnips as they are needed and remember not to discard the greens as these can also be cooked and make good eating.
Maincrop turnips are usually ready to harvest from mid October onwards, so you can be enjoying turnips right up until the end of the year and perhaps even beyond.
Turnips can be stored in the ground until needed over the winter, or lifted for storage elsewhere. Turnips still in the ground can be protected from frosts in colder regions with a mulch of straw or bracken held down with netting or horticultural fleece.
Some turnip varieties recommended for UK growers include:
'Purple Top Milan': This heirloom variety features purple tops with creamy-white bottoms. It has a sweet taste and tender texture, making it ideal for both fresh eating and cooking.
Golden Ball': Known for its smooth, golden-yellow roots, 'Golden Ball' turnips have a mild, sweet flavour. They are less prone to becoming woody even when left in the ground for an extended period.
'Tokyo Cross': A fast-growing Japanese variety, 'Tokyo Cross' turnips produce smooth, round roots with a crisp texture and mild, sweetness. They are suitable for early sowings and can be harvested young for a tender taste.
'Helenor': This hybrid turnip variety produces uniform, globe-shaped roots with creamy-white skin and mild-tasting flesh. 'Helenor' turnips are resistant to bolting and are suitable for both fresh use and storage.
'Petrowski': A winter-hardy variety, 'Petrowski' turnips feature purple tops and creamy-white roots with a sweet, slightly nutty taste. They are excellent for roasting, mashing, or adding to soups and stews.
Once they are fully established, turnips typically exhibit robust health, though seedlings may require protection from common pests like slugs and snails. As members of the cabbage family (brassicas), they are susceptible to similar pests and diseases, including cabbage root fly and clubroot. Birds may also pose a threat by consuming the leaves, necessitating the use of netting for crop protection.
Turnips share pest and disease vulnerabilities with other brassica vegetables. Cabbage root fly, for instance, targets the roots, leading to stunted growth, wilting, and potential plant death, particularly hazardous for seedlings. Employing mesh or horticultural fleece can deter these flies from accessing the roots.
Flea beetles are another concern, leaving small holes in leaves that turn brown over time. Growing plants under horticultural fleece, maintaining soil moisture, and providing adequate fertilization can aid in flea beetle prevention. Strong plants are better equipped to withstand pest attacks.
Powdery mildew is a fungal disease affecting leaves, causing them to shrivel. It thrives in dry conditions, emphasizing the importance of consistent watering to prevent its occurrence.
Clubroot disease induces root swelling and deformation, accompanied by yellowing and wilting of leaves. Unfortunately, there's no cure for clubroot; prevention involves avoiding turnip cultivation in soil previously afflicted by this disease.
Companion planting can help polytunnel growers to achieve the best possible results. There is evidence to suggest, for example, that peas, beans and other nitrogen fixers may be beneficial as companion plants.
Turnips like similar conditions to other brassicas (members of the cabbage family) and they are sometimes put together for ease of crop rotation.
But note that they can share diseases and pests with these other related plants so when grown near one another, should be grown in polycultures with other plants to confuse, distract and perhaps repel pest species and to serve as beneficial wildlife attractants.
MasterClass. (2024) 7 Creative Ways to Cook With Turnips: Tips, Techniques, and Gordon Ramsay’s Glazed Carrots and Turnips Recipe. [online] Available at: https://www.masterclass.com/articles/learn-about-turnips
