When growing onions it is best to grow them from sets, these are immature bulbs that have been grown especially for planting. There are several advantages over growing from seeds, onion sets are much quicker growing, they are less likely to get attacked by pests and disease and they tend not to bolt as much as seed-grown onions.
Soil Preparation
Onions love to grow in good soil, it’s highly recommended that you dig compost or well-rotted manure into the soil in winter before planting. Before planting the onion sets you could also add some general fertilizer to give the sets that extra boost once planted.
Sowing and Planting
Onion sets should be planted in March or April depending on your location. Plant the sets 4 inches apart in rows which are 9 inches apart. When planting you should lightly press the set into the soil making sure that the tip of the set is still showing.
After planting you may also decide to cover the onions with nets as birds tend to pull the sets up, mistaking them for worms. Just covering with a general garden net should be enough just to protect them. Of course, once the onions begin growing the net can be removed.
Looking After The Plants
Keep the plants weed-free at all time, you may wish to use a special onion hoe to do this or alternatively you can do this by hand, either way, is fine.
If you decided not to net the sets after planting you will have to push the onion sets that have been pulled up by birds back into the soil. Don’t worry about this, once the onions have been growing for a few weeks and start rooting this will no longer be a problem.
Harvesting
The onions are mature once the stems of the plants turn brown and fall over. You should leave the plants outdoors to dry once you have harvested them. This will take 7-10 days depending on the size of the onions as well as the current temperature.
Any onions that have a thick neck should be used in the kitchen first as these will not store and onions that are soft or smell bad should be discarded.
Onions should be stored in trays or net bags in a cool, dry, frost-free place away from direct sunlight and you will find that they will keep for up to nine months. Japanese onions will not store and need to be used in a month.