Kohlrabi Azur-Star
A purple-skinned kohlrabi with a flattened bulb, as beautiful as it is tasty.
About the variety. A reliable and easy-to-grow variety with excellent flavour and attractive appearance; very resistant to bolting, grows outdoors or in a greenhouse, and each bulb reaches around 200–250 g.
Itinerário técnico
Um guia de cultivo passo a passo, da sementeira à colheita.
Sow direct one or two centimetres deep in rows and thin to fifteen to twenty centimetres between plants. It can also be raised in trays and planted out at three to four weeks, but without burying the stem, because the swelling must sit above the soil. Sow in succession every three weeks for a continuous supply. Sow from February to April and again in August and September; in summer heat it swells poorly.
It wants firm, deep soil, rich in organic matter and never acid: the ideal pH is between 6.5 and 7.5, and acid soil invites clubroot. It likes settled rather than fluffy soil: firm the ground lightly around the plant after transplanting. Minimum four year rotation away from any other brassica, radish, turnip and rocket included.
It grows best in cool weather, between 15 °C and 20 °C, and is quick: sixty days is enough. Strong heat makes the swollen stem fibrous and hot tasting. The Portuguese coast offers close to ideal conditions and allows harvests over much of the year. Inland in Portugal and Spain, concentrate the crop in autumn, winter and early spring, because from June onwards heat and long days push it to bolt and turn bitter. In France it grows easily from spring to autumn, and in Germany the whole summer works because it is rarely too hot. Light shade over the middle of the day extends the harvest in any warm climate.
Its needs are moderate. One to two kilos of mature compost per square metre worked in before sowing covers most of the cycle. If the leaves pale, one watering with a balanced liquid organic feed halfway through is enough. Never use fresh manure, which burns roots and encourages disease.
Water regularly with no gaps. Any check from lack of water toughens the swollen stem and turns it woody, the commonest fault with this crop. Steadily moist soil gives a tender sweet product.
Hoe often and always shallowly, because the roots are short, near the surface and break easily. The best method is to prepare the bed two or three weeks in advance, let the first flush of weeds germinate, remove it and only then sow: that gives you a decisive head start. A thin layer of sieved compost between the rows greatly reduces later work.
Flea beetle, a small jumping beetle, riddles young leaves with round holes in hot dry weather: keep the soil moist and cover with fine mesh from sowing. Cabbage white caterpillars and diamondback moth eat the leaves from within: apply Bacillus thuringiensis while the caterpillars are small and check the underside of the leaves every week. Cabbage root fly lays at the collar and the larva destroys the root: a cardboard or felt collar around the stem stops the egg laying. Grey cabbage aphid forms waxy colonies on the shoots and is dealt with using potassium soap. A fine insect mesh put on at planting solves almost all of these problems at once.
Clubroot is the most serious disease: it deforms the roots, the plant wilts, and the fungus persists in the soil for close to twenty years. Prevent it with a four to five year rotation, good drainage and a pH above 7.0, corrected with lime. Alternaria makes dark concentric spots and downy mildew a grey bloom on the underside of the leaf; both like humidity, so space well and water at the base. Black rot enters at the leaf margins as a yellow V and is carried by seed and irrigation water. Clear all crop debris at the end and keep it out of the compost heap.
Harvest when the swollen stem is five to seven centimetres across, about the size of a tennis ball. Beyond that it goes fibrous and woody, which is the commonest mistake among growers waiting for something bigger. Cut the root below the swelling and use the young leaves too, which cook like cabbage. Allow about 50 to 60 days from transplanting to the first harvest of this variety. The reference colour is purple, and that is what tells you it is ready.
