The onion belongs in almost every dish and almost every garden. It is easy to care for, needs little space and, harvested right, keeps for months. The only real decision you make at the start is the route: do you plant little sets, sow seed or go for the overwintering type?
All three reach the goal, but they differ in speed, cost, keeping quality and choice of variety. This article sets them side by side, so you choose the route that suits you.
Three routes to your own onion
The classic is the set: little onions raised the previous year that you simply push into the soil from March. It is the fastest and surest route and ideal for beginners.
The seed onion you raise from seed. That needs an early sowing from February or March and more patience, but rewards you with a wider choice of varieties, often larger onions and better keeping quality. The overwintering onion, finally, is planted or sown as early as August, overwinters in the bed and gives the earliest harvest the following early summer.
Which route suits you?
- Set (from March)
The easiest start. Fast, sure, uncomplicated. Planting instead of sowing saves time, but the choice of varieties is smaller and the tendency to bolt a little greater.
- Seed onion (from February)
For the patient with high standards. Raised from seed, wide range of varieties, often larger and better-keeping onions. Needs an early sowing and a weed-free start.
- Overwintering onion (from August)
For the earliest harvest. Planted or sown in late summer, it overwinters in the bed and is ready as early as June, clearly ahead of the spring onions.
- Spring onion (ongoing)
When you only want the green. These bunching onions are not grown into a fat bulb at all but harvested young as spicy tubes, several times over the season.
Bolting: the most common disappointment
Whoever sees a tall flower stalk grow out of their onion in summer is witnessing bolting. The plant switches from bulb to flower formation, the onion turns hard, woody in the middle and will not keep.
Bolting is triggered above all by a cold stimulus on sets that are too large. So the rule is: take small sets under about two centimetres across and do not plant them too early into cold soil. If you notice a flower forming, harvest that onion first and use it fresh.
How you plant onions
Prepare the bed
Sunny, loose and rather lean. Avoid fresh manure or much nitrogen, that gives lots of foliage and poorly-keeping onions.
Plant from March
Set the sets so the tip just peeks out, about 10 centimetres apart in the row, 25 between the rows.
Tend and water little
Hoe weeds shallowly, but do not damage the roots. Onions need little water, and towards the end of ripening none at all.
Harvest when the foliage falls over
Once two thirds of the foliage has bent over and yellowed, lift on a dry day and let it dry off airily.
Sets for speed, seed onions for size and storage. Both love sun, loose soil and little water.
The core rule for onions
Frequently asked questions
Are sets or seed onions better?
Both have their place. Sets are faster, surer and ideal for beginners. Seed onions from seed need more patience but offer the wider choice of varieties and often give larger, better-keeping onions.
Why does my onion bolt and form a flower stalk?
Bolting is usually triggered by a cold stimulus on sets that are too large. So take small sets under two centimetres and do not plant them too early into cold soil. Harvest bolted onions first and use them fresh, they will not keep.
When are onions planted?
Sets go into the soil from March, as soon as it has dried off. Overwintering onions, by contrast, are planted as early as August for the early harvest next year. Seed onions are best raised from February or sown directly into the bed.
When are onions ripe and ready to harvest?
They are ripe when two thirds of the foliage has bent over and yellowed, usually in high to late summer. Harvest on a dry day and let the onions dry off airily until the skin rustles. Then they keep for months, cool and dry.
What soil and how much water do onions need?
Onions like a sunny, loose and rather lean soil. Too much nitrogen and wet encourage foliage and rot instead of firm bulbs. Water sparingly and stop watering altogether towards the end of ripening, that improves keeping quality.
