Sets are usually planted in spring, from mid-March to mid-April. There are also a few varieties for autumn planting, often sold as overwintering or Japanese onions – these are less sensitive to cold, which would otherwise cause bolting. Autumn planting is not suitable in heavy soils prone to waterlogging, as the sets are likely to rot. But they can be planted on Small individual cells, usually in a tray, used for sowing seeds. The resulting seedlings can be transplanted with minimal root disturbance.
Moving a plant from one growing position to another, often from a pot to its final spot in the garden.
Planting outdoors
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 5–10cm (2–4in) apart, in rows 25–30cm (10–12in) apart. Firm the soil around them and water well. Birds will often peck newly planted sets out of the ground, so cover with A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops.
Another planting option is to cover the ground with black weed-suppressing membrane, then plant the sets through slits. There is then no need for weeding, which both saves time and avoids accidental damage to the 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.
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 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.
Planting indoors
If your soil is very wet and cold, you can plant onion sets indoors, then transplant outside once the soil conditions improve. Use modular trays filled with peat-free multi-purpose 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.