Onions are extremely easy to grow from sets, which are small immature onions. If you are a relative novice when it comes to growing things in your polytunnel, you should consider onions as an easy option. If you have some space left over in your polytunnel after removing the summer crops, now could be a good time to plant some sets that will overwinter in your polytunnel before rewarding you will an early crop of onions next summer.
Overwintering onions in a polytunnel can be a good option where winter conditions leave a lot to be desired. Onions outside can suffer if the ground becomes too waterlogged over the winter, and can be plucked out of the ground by birds and other pests. Those in a polytunnel, on the other hand, are somewhat protected and the gardener can decide how much water is required rather than leaving it to the elements.
It is important, however, when choosing and ordering sets to plant in your polytunnel this autumn, that you choose varieties that are suitable for overwinter growing. Some varieties are far better suited to growing in the spring, while some are perfect for growing over the coldest months. The key is to read the descriptions of all sets before ordering them and to make sure that you can provide them with the growing conditions that they need.
Here are some of the good winter varieties of white onion available for sale in the UK:
Here are some options if you would like to grow some red onions:
Here are some options if you would prefer to grow some shallots instead:
One of the good things about shallots is that, though they are smaller than onions, each shallot planted will yield several bulbs for eating or replanting next year.
Sow bulbs at a spacing of around 20 -25cm and mulch with compost or leaf mould. The tips of the sets should just be showing above the soil. Aim to plant onions this month and shallots next. Hand weed carefully little and often as weeds begin to appear in the spring and water when needed, more often as spring and then summer.