Brassica rapa aka Turnip

Brassica rapa is a fast-growing biennial, with some cultivars reaching harvestable size within just six weeks of sowing. As a vegetative rosette (the typical harvest stage for turnips and leafy varieties), plants reach 30–50 cm tall with a spread of 20–30 cm. When allowed to flower in its second year, the branching stem can reach up to 1.2 meters. Growth rate is rapid, making it one of the quickest vegetables to produce a crop.

Brassica rapa is a cool-season crop that performs best at temperatures between 10°C and 20°C (50–68°F). It is highly cold-hardy and tolerates light to moderate frosts, making it ideal for spring and autumn growing. Hot weather causes roots to become bitter, woody, and fibrous, and can trigger premature bolting (flowering). Extended exposure to temperatures below 10°C can also induce bolting in established plants that have undergone vernalization.

Brassica rapa produces bright yellow flowers with four petals arranged in the characteristic cross shape of the Brassicaceae family, each petal measuring 6–13 mm long. Flowers cluster in terminal racemes at the tops of branching stems and bloom from May to August. After pollination, elongated seed pods (siliques) develop, with seeds ripening from July to September. In cultivation, flowering (bolting) is usually undesirable as it makes roots tough and bitter.

Brassica rapa is one of the most morphologically diverse crop species, with major subspecies including subsp. rapa (turnip, grown for its swollen root), subsp. chinensis (bok choy/pak choi, with thick white stems and dark green leaves), subsp. pekinensis (napa cabbage/Chinese cabbage, forming dense elongated heads), subsp. oleifera (turnip rape/field mustard, grown as an oilseed crop), subsp. nipposinica (mizuna, with finely dissected feathery leaves), subsp. narinosa (tatsoi, forming flat rosettes of dark spoon-shaped leaves), and var. parachinensis (choy sum, grown for its flowering stems). Popular turnip cultivars include 'Purple Top Milan', 'Tokyo Cross', 'Golden Ball', and 'Snowball'.

Brassica rapa is exclusively an outdoor plant, grown in gardens, allotments, and agricultural fields across USDA zones 2–9. Sow early varieties from March to June for summer harvest, or maincrop varieties from July to mid-August for autumn and winter use. Some varieties can be started under cloches in late winter. The plant needs full sun, fertile well-drained soil enriched with compost, and consistent moisture. Space plants 10–23 cm apart depending on the desired root size, in rows 23–30 cm apart.

Brassica rapa is propagated exclusively by seed. Direct sow seeds 1–2 cm deep and 2.5–5 cm apart in prepared soil, then thin seedlings to 10–23 cm apart once true leaves appear (spacing depends on desired root size). Seeds germinate within 7–10 days in suitable conditions. For continuous harvest, sow successionally every 2–3 weeks from early spring through late summer. Seeds can also be started under cloches or indoors in late winter for earlier crops.

Common pests include flea beetles (which chew small holes in leaves), cabbage root fly (larvae tunnel into roots), cabbage caterpillars, slugs and snails (especially damaging to seedlings), and aphids. Crop rotation, fine mesh netting, and good garden hygiene are the best preventive measures.

Brassica rapa is primarily pollinated by bees and other insects attracted to its bright yellow flowers, though the species is also self-fertile and can set seed without cross-pollination. Cross-pollination occurs readily between different Brassica rapa subspecies (e.g., turnips can cross with bok choy or napa cabbage) and even with closely related species like Brassica napus. Seed savers should isolate different Brassica rapa varieties by at least 500 meters to maintain purity.

Brassica rapa is highly edible and has been a staple food crop for millennia. Turnip roots are eaten raw (grated in salads with a mild peppery flavor) or cooked (mashed, roasted, in stews). The leaves (turnip greens) are exceptionally nutritious, rich in vitamins C and K, calcium, and potassium, and can be harvested as a cut-and-come-again crop. Young flowering shoots are eaten as rapini or broccoli rabe. Seeds of oilseed varieties yield rapeseed oil, refined into canola oil for cooking or colza oil for industrial use. Best harvested when roots are smaller than a tennis ball, as larger roots become woody and bitter.

Brassica rapa has a modest history of traditional medicinal use. Crushed seeds have been applied as a poultice for burns, and root decoctions have been used in folk medicine for various ailments. Flower preparations were traditionally used as salves. The plant is nutritionally valuable, high in vitamin C (500 mg per 100g dry weight), calcium, potassium, and iron, contributing to general health. These are traditional remedies with limited scientific validation and should not replace professional medical treatment.

Beyond food and medicine, Brassica rapa has limited but notable other uses. Root peelings can function as a natural insecticide. The plant serves as a dynamic accumulator in permaculture, drawing nutrients from deeper soil layers. It is widely grown as livestock fodder and as a green manure or cover crop to improve soil structure and suppress weeds. Rapeseed oil from oilseed varieties has industrial applications including biodiesel production and as a lubricant (colza oil).

Yellowing leaves on Brassica rapa commonly indicate nitrogen deficiency — apply a balanced fertilizer or side-dress with compost. Overwatering or poor drainage can also cause yellowing by suffocating roots. If yellowing appears as V-shaped lesions from leaf edges, black rot (a bacterial disease) is likely the cause and affected plants should be removed. Older outer leaves naturally yellow and die back as the plant matures, which is normal. Clubroot infection can also cause yellowing along with stunted growth and swollen, distorted roots.

Brassica rapa is believed to have originated in Central and Eastern Asia, with wild populations found across Europe and western Asia. PFAF traces cultivated forms to the Mediterranean region (Greece, Italy, Sicily, and the former Yugoslavia). The species was independently domesticated in both Europe (for turnip roots) and East Asia (for leafy forms like bok choy and napa cabbage), leading to the remarkable diversity of cultivated forms seen today. It has since naturalized in temperate regions worldwide, including parts of North America.

Turnip requires a bit more attention and knowledge to thrive, making it a suitable plant for those with some gardening experience.

Turnip should be watered regularly, allowing the soil to dry out between waterings.

Turnip loves a well-draining soil. Perlite and vermiculite help with drainage, while coco coir adds organic matter, so a good potting soil mix will have all three. You can improve store-bought soil by adding some perlite to it.

To ensure optimal growth, the Turnip prefers bright diffused light for 6-8 hours each day. Insufficient light can result in slow growth and leaf drop, so it's important to find a well-lit location for this plant. Place it near a window, within a distance of 1 meter (3 feet), to enhance its potential for thriving.

The Turnip does not necessitate supplementary humidity. Plants primarily absorb water through their roots, rather than their leaves. Hence, the most effective way to supply humidity to your plants is by watering the soil.

The growth of Turnip is gradual and it doesn't necessitate any additional fertilizers. Replacing the soil in its pot once a year should suffice to provide the plant with sufficient nutrition. It's important to keep in mind that plants derive their energy from the sun's rays, not fertilizers.

Ploi does not possess verified information regarding the toxicity of this particular plant. In the event that you, a member of your family, or a pet ingests plant material with an unclear toxicity level, it is highly recommended to seek the advice of a medical professional.

During the cold period, it is common for Turnip to go dormant and their growth may slow down, so waterings should be spaced out more during this period.