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I mostly grow my onions from sets. I start my onion sets off early at the end of January. There’s a couple of good reasons why I do this.
1. Onions need a long growing season to mature and ripen, they are also sensitive to daylight & temperature. As the summer days grow shorter it can trigger the onion to go to seed before the onion is ready to be harvested..so the earlier you start them off in modules, the better. It gives them opportunity to put on some extra growth early on.
2. Birds tend to pull up fresh onion sets and toss them around, mistaking them for snails, or they do it for a laugh…who knows! But, sets you have started off early are less desirable, due to their plumes of foliage…it puts the birds right off.
Plant onion sets in compost filled modules, root down, around 1/3 depth. See below.
I plant out March/April once they have established healthy foliage. Plant 10-15cm apart, with roughly 30 cm between rows.
Onion sets will reach maturity around 80 days after planting. If growing from seed, 100-120 days. Onions require a free draining soil and a sunny position. I also like to dig in some well rotted manure before planting.
Onion Scapes, the free gift with every onion plant! As soon as these appear, remove them! They will steal energy from the plant and stunt the growth of the onion bulb. But don’t throw them away…eat them! Eat raw in salads or cooked in stir fry’s or pasta dishes. They have a mild garlicky onion flavour, delicious!
Harvest Onions when the leaves begin to flop over or you see the edges browning. Dig them up using a fork, try to not damage the roots (they store better with intact roots) Leave them to dry out in a sheltered sunny spot for about a week. If you wish to store the onions long term, you then need to cure them. This can be done by spreading them out on a table, or hanging them up, or using racks, make sure the area is dry and airy, a polytunnel or greenhouse would be ideal. Let them dry out for 2 weeks until the skins are dry and papery and the roots are bone dry and wiry.