Onions - Growing Your Own / RHS Gardening

Sets are usually planted in early to mid-spring, for harvesting from July to September. Overwintering (Japanese) onion sets can be planted in autumn, for harvesting in June and July – these are less sensitive to cold, which would otherwise cause bolting.

Planting outdoors

In prepared ground (see above) plant sets 2cm (¾in) deep in drills or gently push them into loose soil, so the tip is just showing at the surface. Space them 5-15cm (2–6in) apart (wider spacing will give you larger bulbs These are fleshy, rounded, underground storage organs, usually sold and planted while dormant. Examples include daffodils, tulips, hyacinths, lilies, onions and garlic. The term is often used to cover other underground storage organs, including corms, tubers and rhizomes. ), in rows 20–30cm (8–12in) apart. Firm the soil around them and water well. Birds will often peck newly planted sets out of the ground, so protect with biodegradable fleece or netting until they’ve rooted in.

Planting indoors

If your soil is very wet and cold in early to mid-spring, you can plant onion sets indoors, then transplant them outside when soil conditions improve.Avoid autumn planting if your soil is heavy and prone to waterlogging during the winter months, as the sets are likely to rot. But they can be planted in modules Small individual cells, usually in a tray, used for sowing seeds. The resulting seedlings can be transplanted with minimal root disturbance. indoors instead, then transplanted Moving a plant from one growing position to another, often from a pot to its final spot in the garden. outdoors in spring, which still gives them a head-start.

Use modular trays filled with peat-free multipurpose compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. and plant one set per module. Keep somewhere cool and bright, an unheated greenhouse is ideal.

Planting in containers

Onions can also be grown in large containers if you don’t have space in the ground or your soil is too damp. Use peat-free soil-based compost Soil-based compost is a potting compost that includes sterilised soil/loam in the mix. As loam contains sand, silt and clay, it does not rot down like organic materials, so adding soil/loam to compost ensures it is longer lasting – it is often used for shrubs in pots and will last 3–4 years without the need to be replaced. and a container that’s at least 45cm (18in) wide and deep. Plant the sets as described above.