Itinerário técnico
Um guia de cultivo passo a passo, da sementeira à colheita.
Sow direct half a centimetre to one centimetre deep, or in trays for transplanting at four weeks, and thin to twenty five or thirty centimetres. Germination takes five to ten days. Late summer sowings are best, because shortening days prevent bolting and the autumn cold softens the bitterness.
It wants deep, loose, free draining soil at a pH between 6.0 and 7.5. It has a taproot and appreciates deeply worked ground. It is not demanding in fertility.
It is a cool weather crop, between 15 °C and 22 °C, and cold hardy: it takes light frost and the leaf sweetens after it. Heat and long days cause bolting and intense bitterness. This is a cool season crop and heat is its main enemy. 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. In Italy follow the Iberian calendar in the centre and south, concentrating the crop in autumn and winter, and the French calendar in the north, where the Po valley summer rarely makes it bolt too early. 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 to keep the leaf tender and reduce bitterness. Water shortage strongly intensifies the bitter taste and toughens the leaf. Water at the base in the morning.
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.
Slugs and snails hide in the heart of the plant and are the main problem: collect them at night and use an ash barrier. Aphids settle in the central leaves and are treated with potassium soap. Leaf miner draws tunnels that are simply removed by hand.
Botrytis and sclerotinia rot the collar and heart in wet autumns and winters, above all on crowded plants or ones planted too deep. Space well, plant with the collar at the surface and ensure drainage. Downy mildew appears on the leaf underside in damp weather.
Pick leaf by leaf or cut the whole plant at ground level, leaving the root to resprout. To reduce bitterness, cover the plant with an upturned pot for ten to fifteen days before harvest: blanching softens the flavour considerably and is the traditional practice with this crop. The reference colour is red with white veins, and that is what tells you it is ready.
