Sowing

Sow the black seeds about 1cm deep in March-April indoors or in hotbeds. Keep the sowing warm during germination, 20-25°C, preferably. When the seedlings have sprouted put them in a light, airy, cool place. Especially during the last weeks before setting it is important that the temperature not be too high (max. 15°C), because the onions may begin to swell to early believing it to be summer. The plants become sturdier if the foliage is cut now and then to a height of 6 cm. Eat the cut off tops in the same way as spring onion. Set out in a plot as soon as the soil has warmed up a bit and the risk of frost is over. Set the onions shallowly and firmly! Onions develop for a long time and can only be sown outdoors in the southern parts of the country. 

Spacing

Sow 40-60 seeds/meter. Keep a mutual distance of 2-5 cm during pre-cultivation. Keep 10 cm between the plants outdoors and 25-50 cm between the rows! 
Sow 4-500 seeds in a 10 cm wide strip for sets!
250-300 seedlings/m is just about right for growing onion sets.

Harvest

Harvest the onions in dry weather! As soon as the tops of ¼ of the onions have begun to wither and fall, break down the tops of the rest of the onions. Pull them out in a few days and if the weather is dry and mild they can be allowed to remain on the ground for ab. 1 week to dry.  It is, however, safest to place them under a roof in an airy, dry place. You get the best keeping qualities if the onions are allowed to dry in warm air (30°C) for 1 week before trimming and placing them  in a dry, cool space, free of frost.

Seed

200-300 seeds/g, one portion yields 75-100 good seedlings for setting and is sufficient to sow a few meters directly and 20-30 g for 100m.  
A portion contains about 150 seeds.