Avoid planting in ground where onions or shallots have been grown in the last three years. Choose a sheltered, sunny site, which has been manured in the autumn or early winter. Spring planting onion sets can go out between early March and mid April when the ground is not frozen or too wet.
If your soil is heavy, you can start you sets off in cell modules in an unheated greenhouse or cold frame.
Plant sets in shallow drills or use a trowel. When you have finished planting the sets the tips should be only just protruding above ground, if you plant too shallow the birds are likely to pull them out. Space onions in rows 25cm (10in) apart. For medium sized onions, space the sets 10cm (4in) apart in the row; a wider spacing of 15cm (6in) will give larger bulbs. Space shallots in rows 25cm (10in) apart, with 15cm (6in) between bulbs.
During the first few weeks after planting check on the sets to make sure they have suffered neither bird damage nor frost heave. If this happens it is best to take the sets right out of the ground and replant. When the sets are maturing in the summer it is essential not to over-water the plants.
It is particularly important to regularly hand-weed or hoe around the plants and between the rows. The only main pest to look out for is the Onion fly. It lays its eggs in Spring on the neck of the onion and the developing larvae will tunnel into the onion and destroy it. Hoeing around the onions will expose eggs if they are there. These flies are attracted by smell so if you are growing from sets and do not thin the plants out it shouldn’t be a problem.
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