Written by Bernie
A look at the best ways of growing onions successfully, from personal experience and that shared over the years from the local allotment members.
Seed or Set
The advantages of set over seed are as follows: sets are more reliable, easier to grow and can be bought heat-treated to prevent bolting. Seed onions are the choice of specialist growers who nurture the seed onions for a long period of time; traditionally "mammoth" onion seed should be planted on Boxing Day. They are also a lot cheaper to buy than sets. I have always found that the cost per mature onion works out pretty much the same as I lose many young seedlings in the transplanting process. I also do not have the time to go to the allotment every day whist the seedlings are young to tend to them so have found that it is just as economical to grow sets. If choosing seed it is worth noting that onion seeds do not germinate above 21 degrees centigrade so you must ensure that the green house or windowsill is not too hot.
Everything is edible
With onion seed, the thinnings can be used as spring onions if they are left to grow to the right size, the young onion plants can be used virtually at any time. Should your onions bolt then you can shave the small flowers off and eat them raw in a salad or add to pasta or sauces, don't however try to store an onion that has bolted. They tend to rot in storage in a similar way to the "bull necked" ones you sometimes see
Onions are biennials that spend the first year building up a "bulb" of reserves, which is used to promote a huge head of flowers in the second year. We obviously harvest onions at the end of the first year after the bulb has been produced. Folklore has it that onions continue to grow more and more leaves until the day length reaches 16 hours and then concentrate on producing a bulb. Obviously the more leaves that an onion can produce before this magical day, the more leaves it has to use to produce a bigger bulb at the end of the first year.
I always soak onion sets overnight before I plant them out. It seems to give them a head start and means they will start to grow quicker and therefore have less opportunity to be lifted by mice. If I want large specimens then they will be planted 9 inches apart, but usually 4 inches apart as I would prefer to have more smaller onions than fewer large ones. The reasoning behind this is fairly simple; I very rarely need a 2lb onion as opposed to a couple of smaller ones! And if I am hit with any form of disease, having more rather than less makes logical sense. Onions, due to the nature of their leaves, do not provide any ground cover to strangle weed growth and therefore require hoeing regularly, ensuring shallow roots are not cut with the hoe. Never hoe deeper than 1 inch into the ground for this reason.
Onions will, depending on the weather, be starting to ripen during August and September. This can be hastened by bending over the leaves slightly to aid the drying process however it should be noted that the more interference that you have with the process, the less likely the bulbs are to store with any longevity. This also applies to the roots; lift them if you must, but ensure that the base of the onion where the roots come out is not damaged in any way. The damage will allow rot to enter the bulb. Onions once lifted should be dried for as long as possible on top of the ground before storing in a cool frost-free dark dry place. Onion nets and strings all look very nice but mean that the stored bulbs are in contact with each other and should a rot set in it will spread very quickly. A less "romantic" but more reliable way is to lay them out, ensuring that they are not touching each other, on newspaper on the shelf in the shed.
With thanks to hardworkinghippy, Res and Naomi for supplying the pictures.
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