Onions are a staple ingredient in most peoples cooking and are one of the easiest vegetables to grow. Many allotment plots include rows of onions as part of the course. Now is the time of year to think about planting overwintering onion sets. Although they can also be planted in the spring, autumn planted onions tend to produce a better crop, having had a few more months to get established.
There are many different varieties of onions that you can grow. The most common type of onions are yellow onions, red onions, spring onions, and the larger salad Spanish onions. Onions are a member of the Allium family, that also includes spring onions, (scallions) shallots, leeks, garlic and chives.
Onion can either be grown from sets or seeds. Sets are miniature bulbs that when planted will just swell to a larger size. Growing onions from sets is the easiest way but it is more economical to grow them from seed as you generally get around 200 seeds per packet! Seed onions also tend to produce crops that store better.
Onion sets need to be spaced 6″ (15cm) apart each way or spaced at 4″ (10cm) in rows 8″-12″ (20-30cm) apart. Closer spacing produces smaller bulbs but there is no point going over 6″ (15cm) apart.
Carefully make a small dip in the soil using a small stick or a dibber and gently position the onion set, pointed end upwards. A sprinkling of general fertiliser or blood, fish and bone to the soil about a week before planting will help the bulbs to get established. Ensure that the top of the bulb is showing and that it is not pushed into the soil too firmly as this could damage the root system.
Its best to cover the newly planted onion sets with some sort of protection such as cloches or netting to prevent birds from eating them. Regular hoeing between the bulbs helps to keep them weed free but be careful not to damage the bulbs.
Onions are ready to harvest as soon as the leaves turns yellow and bend over. Overwintering ones are generally ready in June whereas spring planted sets are ready around August. Gently lift the bulbs from the ground, remove any excess soil and leave them to dry in a warm, dry place for at least 2 weeks. After that, tie or plait the stems and store in a cool, dry place until needed. I tend to use either my unheated greenhouse or shed.
Pests, problems and diseases
Certain varieties of onions have a habit of bolting. This just means that they start to go to seed and concentrate on producing flower heads rather than swelling the onion itself. Not all varieties of onions will bolt and this can be prevented by planted ‘heat treated’ sets. Onions have a few pests and diseases. Details of the most common ones can be found using the links below.