Growing onions is not without a few problems by way of pests or diseases, but even in a bad year, they will still produce a crop worth the bother. In a good year, you will be able to help your friends out as well!
Here, we talk of the standard globular onion, but much of the cultivation and soil treatment is applicable to the smaller pickling onions as well.
Most garden soils will suit onions as long as it is free draining and not subject to getting waterlogged.
There are a few different methods of growing your own onions in the garden so simply try the method that fits in with your schedule and facilities.
Onions are a good crop to grow for financial reasons, take up little space, and can be grown amongst a few other crops quite well. In particular they are happy alongside Brassicas of all types. They should not be grown alongside beans or any other members of the legume family, but are happy to be planted in soil that was occupied with legumes the year previous.
Manuring of the soil for onions if it is to happen, should take place at least 6 months prior, or they can be given fertiliser or liquid feed through their growing period.
The two basic styles of growing are either by planting onion sets, or growing from seed. Both methods have advantages and disadvantages. Some will swear by sets, and others prefer seed.
If you decide upon onion sets, then your time options are more varied than the tighter timetable of growing from seed.
The choice of onion varieties is restricted if you decide to grow from onion sets. Don't let that deter you, for the varieties which are available are the well tried and tested types.
There are two basic types of onion sets available...
In the autumn it is possible to obtain a Japanese Onion Set, which can be planted and overwintered to give an early crop of onions in the late spring. However, these are no good for storing, so grow to eat.
The Onion sets available in the spring are generally good croppers and storing varieties. Sturon is normally available, and is a good variety for general purpose and also storing through the winter.
If your soil is well prepared, then simply push the onion sets into the ground at a planting distance of 10cm. 30cm apart for the rows if you are planting more than one row. Just push into the soil so that the neck of the small bulb is at ground level. You will need to push them back into the ground from time to time, if they get lifted by frosts or birds. Once they have rooted into the ground, there is no such problem.
Sets have the advantage of missing out on onion fly to a large degree.
This is a slower method, but cheaper, and with a wider range of varieties available.
Sow the onion seed in early spring in a warm greenhouse or propagator. These can be directly planted into the open ground in late spring. They are quite hardy, but will need proper hardening off before planting out
It is best to sow them into seedling units - two or three per cell. This will avoid too much disturbance with pricking out etc. Simply chose the strongest seedling to stay and discard the weakest. A good little trick is to plant some of the cell units that have a few seedling in it. This way you will get a clump of smaller onions. These are generally harder than the single bulbs, and store very well.
In the case of sets or seedlings, it is important to try and rid the plot if weeds before planting out. You need as little disturbance as possible once the onions are planted. Onion bulbs damage easily and any damage alerts the onion fly to a potential home for its eggs and young maggots!
Once the onions are ripe, allow the foliage to die down and fall over naturally. Do not bend the stalks over in the mistaken belief that you are exposing the bulbs to sun for ripening. You are damaging the stem, and allowing disease and pests easy access.
There are four diseases that can attack your onions; being white rot, downy mildew, neck rot and rust. All four are rare if grown on clean ground and not the same area as used previously. Any visibly affected plants should be removed immediately and burned
Onion fly is the main pest, though not in all areas. Growing from sets helps to avoid them, but as a safety measure, cover the row with fine net or garden fleece.
Water only if necessary and keep the air circulating between the rows at all times as this helps with the prevention of fungal diseases – mildew especially.