Growing Onion

The onion is a true all-rounder in the kitchen and garden. With its sweet yet pungent flavour, it enhances countless dishes and is not only delicious but also healthy. It belongs to the amaryllis family and is one of the oldest cultivated plants known to humanity. The onion is perennial but is usually grown as an annual crop, as it forms its edible bulbs in the first year.

The variety of onions is vast: from mild spring onions to classic summer onions and hardy winter onions, there are numerous types that differ in shape, colour and taste.

In the garden, the onion is a valuable plant that not only tastes great but also acts as a companion plant against pests. It loves sunny, warm spots and humus-rich, well-drained soil. The onion is relatively undemanding but needs careful attention, especially in the early stages when it struggles to compete with weeds.

It also has a long history as a medicinal plant, particularly for colds and earache. As an emergency home remedy for bee and wasp stings, cut an onion in half and rub it on the sting. It works – even our daughter confirms this. Sulphur compounds in the onion juice break down the venom and ease the pain.

Spring and Winter: show the times for growing from seed

Spring 2 and Winter 2: show the times for growing from sets

You can grow onions in several ways: by direct sowing, starting indoors, or planting sets.

For direct sowing, sow from early March to late April, depending on your region and the weather. Sow the seeds shallowly, about 2 cm deep, in rows 25 cm apart. Thin the plants to 5 to 10 cm apart once they're big enough.

Cultivation indoors or in a greenhouse often begins in mid-February to early April in order to obtain young plants for planting in mid-April to mid-May. Sow the seeds across the surface in pots or trays and germinate them at an ideal temperature of 15 to 20 °C. Plant the seedlings out carefully – don't set them too deep. The bulbs should sit on the soil surface with only the roots in the ground.

Onion sets are a handy alternative, especially at higher altitudes or if you're sowing late. Plant them from late March to May, spacing them about 10 cm apart, with the tip just poking out of the soil. Sets grow faster, but they're more prone to disease and offer less variety choice.

Spring onions can be sown from March to August for a continuous harvest. Sow them shallowly (about 1.5 cm) with a row spacing of 20 to 25 cm.

To produce your own sets, sow onion seeds in spring (March–April) about 2 cm apart. Harvest them after roughly 8 to 12 weeks, once they're the size of a hazelnut. In Gertrud Franck's method, this is done in the C-rows.

Onions love sunny, warm spots with good air circulation. An open, breezy location is ideal so the foliage dries quickly and diseases are kept at bay. Onions don't cope well with shade, as they produce less bulb mass and become more prone to disease.

The soil should be loose, rich in humus and nutrients, with good water retention. Medium-heavy soils with some clay content are optimal. Pure sandy or heavy clay soils are less suitable, as they either dry out too quickly or stay too wet. Before sowing, thorough soil loosening and working in compost is recommended.

In the early growth stage, onions are sensitive to waterlogging and soil compaction. Good soil preparation and care are therefore essential.

The variety of onion cultivars is vast, ranging from mild spring onions to classic summer onions, hardy winter onions and bunching onions. Colours vary from white through yellow to red and violet.

Summer onions generally store well and come in a wide range of shapes, from flat-round to pear-shaped. Winter onions are cold-resistant and suited for autumn and winter growing. Bunching onions form small bulbs with long stems and are eaten fresh.

Shallots are closely related but differ in their elongated shape and growth in clusters. They have a milder flavour and are often used raw.

Onions are relatively undemanding but need careful weeding in the first few weeks, as they struggle to compete during this phase.

Water moderately and in the morning, so the plants can dry off by evening. This reduces the risk of fungal diseases like downy mildew.

Too much water, especially just before harvest, can lead to glassy onions. Once the tops have bent over, stop watering altogether.

Fertilising is usually unnecessary if the soil has been well supplied with compost. Onions are light to moderate feeders. Too much nitrogen promotes leaf growth at the expense of bulb formation and storage life.

Onions are prone to a range of diseases and pests that need particular attention in organic growing. The most common fungal disease is downy mildew (Peronospora destructor), which spreads quickly in cool, damp weather. You will see pale patches on the tubular leaves, followed by a greyish-violet coating.

To prevent it, choose an airy spot, keep the bed free of weeds, water only in the morning and spray with horsetail tea. Onion rot (Fusarium oxysporum) leads to small, weak bulbs with poor roots and yellowing leaves. Affected bulbs carry on rotting in store.

Pests such as the onion fly lay their eggs on the leaves, and the larvae tunnel through the tissue and damage the bulb. Insect netting keeps them out, and growing onions alongside carrots can help too. The leek miner fly can also cause damage.

Stress from drought, sowing too late or overwatering can lead to yellow tips, thick necks or bolting.