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May 152007

A lot of people are put off growing onions because they grow under the ground and seem a bit mysterious compared to, say, a tomato… where at least you can see what’s going on! We’ll try and unveil some of the secrets for you!

Like garlic, onions put on their leaf growth during the cool months, then switch over to putting the energy from the leaves into the bulbs when the weather heats up. We’re told by the vegetable master, Peter Cundall, that this is because onions concentrate on adding additional ‘scales’ until the longest day in December, then they fill out those bulbs dramatically. The more scales, the fatter the bulb will be. The size of the onion can also be foretold by the number of leaves on the plant at maturity – the rule is: 1 leaf per ring on the bulb.


In general, plant onions in autumn – early spring 10-15 cm apart in well drained soil. Plant in a different place each year, preferably on a 5 year rotation around the garden or the patch. Onions like a limed soil, so if you haven’t limed the area in the last year or so, sprinkle around some dolomite or garden lime. If you sow onions from seed they should come up within 2-3 weeks. Seed germinates readily between 2 and 27 deg C. Be careful not to overwater!


It’s best to not fertilise onions at planting, rather to plant them in soil that was fertilised for the last vegie crop. Too much manure or blood and bone in the soil can encourage maggots and rot, not very yummy! It’s ok to add some wood ash or potash though.

If this doesn’t happen, too much fertiliser can result in loose and soft bulbs which won’t keep for very long. Salad onions, like white Spanish, are grown to eat fresh rather than store so a bit more fertiliser is OK for them.


There are onions grown for storage and onions grown to eat fresh. The best of the long keepers are brown Spanish Brown and Creamgold. Both do well planted in July. If grown well, you’ll harvest you onions in Summer to early Autumn and the long keepers should store until the following spring.

Salad onions are softer, milder, are grown to eat fresh and don’t keep very long.

In general, they are ready for harvest in 18-26 weeks or when the tops dry up a bit. Otherwise, the particular variety will give you specific harvest times on the pack or tag.

Friends of the Onion

If you have the room, leave space for a row of carrots to be sown in between onions, as they repel onion pests, and onions repel carrot pests. They are happy companions and are also said to improve each others yield.

Enemies of the Onion

Peas, beans and other legumes. Weeds.


Fry, roast, stewed or pickled. May be frozen. Medicinally used as a blood purifier, antibiotic and disinfectant.

Tip: Be gentle when transplanting seedlings or you can trigger them to bolt to seed.

White Onions

White onions are a mid to late season variety with white skin and flesh. Plant autumn – mid spring 10-15 cm apart in well drained soil for harvest in 18-26 weeks or when the tops dry and fall over. Plant in a different place each year.

The Mystery of Long, Intermediate and Short Day Onions

Onions begin with growth concentrated on roots and leaves, then begin to form bulbs when daylight hours reach a particular length. Long Day varieties do best in areas that have more hours of daylight in the summer (14-16 hours). Long day onions are excellent keeping varieties. Intermediate onions are the most widely adapted, being best for the middle latitudes (12-14 hours of sunlight per day). (Creamgold is an Intermediate onion). They can be used in northern regions and in the south where daylight hours reach 10-12 hours per day. Short Day types are best suited for southern climates, when day length reaches 12-14 hours of sunlight, and are generally planted in the winter or early spring.