You may think winter turnips and swedes only have a place in the traditional allotment. But many smaller turnip varieties take as little as eight weeks from sowing to eating, so they make excellent catch crops.
Kohl rabi is a continental relative of the turnip and is a decorative substitute worth considering in even the smallest garden.
The larger varieties of turnips and all the swedes (originally an abbreviation for Swedish turnip, after their origin) are slow-growing and produce large roots that can be stored for winter use. The smaller, summer turnips and kohl rabi, which produce an edible swollen stem above ground, rather than a root, are grown as summer crops.
Summer turnips and kohl rabi are useful catch crops. Because they are related to the larger and slow-growing members of the cabbage family, they are usually grown in the same crop-rotation group. Use them to fill space from February to June before winter crops such as sprouting broccoli or winter cauliflowers are planted out.
Sow them in May between Brussels sprout plants. These will not need all their allotted space until later in the summer, by which time the catch crop is ready to be harvested.
Grow them after an early crop of broad beans or early peas have been cleared, so they benefit from the nitrogen left by the previous crop.
Calendar
Both crops need a moist, fertile soil, but will tolerate light shade during the summer. They also do best on a slightly alkaline soil. Because it forms globes above rather than below ground, kohl rabi is better able to cope with heavy soil than turnips.
February
An early sowing of turnips can be made under cloches. In colder areas or for growing outside, wait until March.
March
It should be safe to sow turnips directly outside, but leave kohl rabi until the end of the month. Both crops can be grown close together to produce lots of small baby roots. They can be sown little and often through the summer.
Prepare the soil by forking and raking to create a seedbed. Work in a reasonable amount of balanced fertilizer and water the soil a couple of days before sowing if it is dry.
Make seed drills 1.5cm deep and 15cm apart. Sow the seed thinly, to avoid having to thin out later. If the soil is dry, water the bottom of the seed drill before sowing. Both crops can be used as a catch crop and can be multi-seeded in pots.
Both will succeed in containers, provided the compost is kept moist. Scatter the seed thinly and cover with about 1.5cm of compost. Thin the seedlings to roughly 7.5-10cm apart. In an ornamental border, kohl rabi (particularly one of the purple varieties) is the best choice. Sow small patches and thin out later, or start the seed off in pots for transplanting later.
April
Sow another batch and thin out the earlier sowings to give roughly one plant every 10cm for larger roots, or 3cm for baby roots. You do not need to be too thorough, as the roots will push apart as they grow.
May-June
For tender roots, the plants should grow rapidly without any check to their growth. This means that in dry spells they should be watered regularly -give a generous soak once a week to wet the soil thoroughly. Watch out for flea beetle, which can seriously damage the young leaves. If necessary, dust or spray with derris.
The first roots should be ready in early May. Start to pull them as soon as they reach golf-ball size.
Sow further batches at fortnightly intervals if you want to extend the harvest into autumn.
