Bulb onions are classified by day length – short (early season), intermediate (mid) or long (late) day length. This corresponds with the hours of daylight needed for bulb formation. It is important to match the variety with local conditions. Early onions are planted in autumn, mid season in winter and late season planted in late winter or early spring.
We also have perennial onions – ever ready onions and tree onions – growing, which are much easier to grow than the bulbing onions, as well as plantings of leeks and onions in some years. The tree onions produce single or double bulbs at the base as well as smaller bulbils at the top. Eat the basal ones and use the tops for propogating. The plants tend to do this themselves (they’re also called walking onions) because the tops bend over when mature,allowing the bulbils to touch the ground and germinate.
Autumn – Plant long season (early) types from March to May as seeds or seedlings. When transplanting seedlings, trim the tops to about 4cm length and also the roots if they are too lanky. Rows 30-40cm apart and thin the plants over time as they grow, first to 2-4cm apart and later to about 10cm. The base of the bulb should be just below the soil surface.
Winter – Plant mid and late season varieties in June and July, as above.
Spring – Feed with compost, potash, foliar fertiliser when bulbs start to form. Weed and mulch. Water but don’t overdo it or the bulbs will rot. The bulbs will push up to the surface as they grow, so don’t hill the soil around them.
Summer – Keep up the weeding, onions don’t compete well with other plants. after 6 – 8 months the bulbs will be nearing maturity. The leaves will tend to droop and fold over. Cure them as for garlic when you lift the bulbs, but for a week or so, not three. Handle carefully to avoid damage and disease. Store in a cool dry place.
Generally – Apart from getting the variety right, make sure the soil is not overly high in nitrogen when you plant or else the onions will grow leafy tops at the expense of bulb fomation. The brown onions and long day length varieties store better than white onions and early, short day onions.
Eating – Roasted whole, caramelised, pickled, in tarts, and everyway.