Red Onion

You grow the red onion as an annual summer crop: plant sets in March/April, harvest from July/August as soon as the foliage bends over and yellows. There is nothing to overwinter. Store the harvested onions dry, cool, dark and airy (e.g. in a net), and plant new onions next spring; if you want to harvest as early as June, you can instead plant hardy overwintering sets in September/October, which overwinter in the soil.

You propagate the red onion in two practicable ways: by sowing seed or via onion sets (small raised bulbs that you plant again the following year).

Sowing: Start the onions indoors on the windowsill or in an unheated greenhouse from February. Around 18 to 22 °C is ideal; the seed needs light and germinates slowly (about 1 to 3 weeks, longer in cold soil). Sow the seeds 1 to 2 cm deep in seed compost and keep them evenly moist. From the end of February to March you can also sow directly outdoors, as soon as the soil is frost-free and has dried out. Row spacing 20 to 25 cm, later thin to 5 to 10 cm in the row. This method is inexpensive and offers the greatest variety choice; onions raised from seed usually store well.

Onion sets: Onion sets are not true bulbils, but small first-year bulbs that arise from particularly dense sowing the year before. If you want to raise them yourself, sow seed very densely (broadcast), let the little bulbs ripen well and dry them in an airy, warm place. Store them cool and dry over winter. In March/April, as soon as the soil is frost-free and sufficiently warm, plant them tip upwards so deep that the shoot just peeks out, about 10 to 15 cm apart in the row and 25 cm between rows. Onion sets sprout faster than seed and are ready to harvest earlier, so they are more reliable. Note: unlike the tree onion or the shallot, an ordinary bulb onion does not form natural daughter bulbs or bulbils on the bulb. You can, however, keep the smallest usable onion of your own harvest as a set and plant it again the next year.