Planting Onion Sets in October: A Head Start in Your Balcony Box
Plant winter onion sets now and you can harvest in early summer – even on a balcony. Everything you need fits in a single box.
Onions are usually seen as a spring crop, but there is another way: special autumn varieties can go into the soil right now and get through winter on their own. For balcony gardeners this is ideal, because the box often sits empty over winter.
Why autumn onions work
Not every onion set is suited to autumn. Varieties such as ‘Radar’, ‘Electric’ or ‘Troy’ are bred specifically for planting in October. They grow roots and a short tuft of green before winter, rest during frost and push on quickly in March. Ordinary spring varieties would be more likely to fail over winter or to bolt in spring. It is best to buy small sets, roughly 10 to 21 millimeters (about 0.4 to 0.8 in) across, because they bolt less often than large ones. Ideally, plant from mid-October to early November, as long as the soil is still workable.
The right box
Choose a balcony box or pot that is at least 20 cm (8 in) deep and has drainage holes. Wet feet are the most common reason onions fail over winter. A layer of expanded clay or coarse gravel at the bottom helps; on top goes loose, low-nutrient vegetable soil, ideally mixed with a little sand. Fresh fertilizer is not needed now. The spot can be bright in winter; come spring, the box should get about six hours of sun a day.
How to plant them
Set the onions about 10 cm (4 in) apart in rows, pointed end up. Between rows, about 15 cm (6 in) is enough in a box. The tip should just peek out of the soil or be only lightly covered. Onions planted deeper rot more easily in a wet winter. Press the soil down gently so the onions are not pushed upward by rain or frost. Water once after planting, and that is all they need for now.
Getting through winter
Onions tolerate frost well, but the soil in a box gets chilled through more than in a bed. Place the box against a sheltered house wall and raise it on feet so water can drain. In a hard, lasting freeze a loose cover of leaves or twigs helps. Water only on frost-free days and very sparingly. After cold spells, check briefly whether any onions have been heaved out of the soil and gently press them back in.
Harvest in early summer
From spring on you can use the green tops like green onions. Take only a few leaves per plant, otherwise the bulb stays smaller. The bulbs themselves are usually ready in June or July, once the foliage turns yellow and flops over. Pull them and let them dry for a few days somewhere airy and dry. Because they finish earlier than spring-planted onions, you can replant the box straight away.
Keep track of your plan
Note down the variety and planting date so you know exactly when harvest is due in early summer. In Rootivo you can set up the box as a bed and see in the planting calendar when it becomes free again. You can plan the follow-up crop, such as lettuce or radishes, right away.