Growing Spring Onions in Scotland: The Complete Guide

Allium cepa (immature bulb onion)

Spring onions are one of the quickest, lowest-effort crops you can grow, ready in about two months and easy to keep coming in small batches.

Spring onions ask for little beyond regular small sowings and a weed-free row. Pulling them young is the point, not a compromise: young onions are sweet and mild and become stronger as they grow. Sow a batch every few weeks through the growing season, and add a hardy autumn sowing for a crop ready before anything sown fresh that year.

Sowing

Sow outdoors from March, in small batches every few weeks, for a steady supply from spring through autumn rather than one glut. An early indoor sowing in modulesA tray divided into small individual cells, each sown with its own seed or seedling, so each plant grows undisturbed roots until it's ready to plant out. Full definition → in March is also an option if you want a head start on the first batch. Make a shallow drillA shallow, straight groove made in prepared soil for sowing seed into, at a set depth so germination and rows are even. Full definition → 1cm deep, and thin seedlings to about 2.5cm apart once they come up, using the thinnings in salads rather than wasting them.

Leave about 20cm between rows. Closer spacing encourages downy mildew, so thin properly rather than leaving a dense row.

Sowing a hardy, overwintering crop

A hardy variety such as White Lisbon can be sown in late summer or early autumn, protected through harsh or cold weather with a clocheA small, portable clear cover placed over an individual plant or short row to trap warmth and keep off wind, rain and pests. Full definition → or biodegradable fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition →, and left to overwinterKeeping a plant alive and intact through the cold months, whether left outdoors, moved under cover, or stored dormant. Full definition → for harvest from the following March, well ahead of anything sown fresh that year. Treat it as a separate sowing on the calendar.

Rotation and white rot

Spring onions share their pests and diseases with bulb onions, shallots, garlic and leeks, so keep them together in your rotationMoving each crop family to different ground each year, on a multi-year cycle, so pests and diseases that build up in soil don't get a repeat host. Full definition → plan and don't follow one with another on the same ground year after year. White rot is the exception to what rotation can fix: it causes yellowing, wilting and decay of roots and bulbs, its sclerotia can remain in soil for at least 15 years (RHS), and no chemical treatment is available to gardeners. The defence is not to bring it onto clean ground on plants, tools or soil.

Varieties

Guardsman (vigorous, with tall upright leaves, slow to produce bulbs) and Apache (purple-skinned, mild and fast growing) also hold the AGMThe RHS's Award of Garden Merit: a UK-wide trials award for reliable performance, not a Scotland-specific recommendation. Full definition →, a UK-wide award rather than a Scottish one. Photon has straight, elongated white stems and a long harvest period but no AGM.

Also worth considering

Best Spring Onion Varieties for Scotland → compares all named spring onion varieties head-to-head, with the practical detail that doesn't fit in a summary card.

Care

Water young plants until they're established, then only during prolonged dry spells; containers need more frequent watering because the compost dries out quickly in hot weather. Weed regularly: hoe between rows and hand-weed between plants, since weeds compete for light and moisture. Before sowing, dig in a bucketful of compost or well-rotted manure per square metre, because the root system is limited.

Harvesting

Pull at about two months from sowing, young and small, around 15cm tall with the bulb no more than 1-2.5cm across, for the sweetest, mildest flavour. A 3m row averages 250-300 onions (Gardener's World).

A perennial alternative

If replanting every few weeks isn't for you, bunching onions are a perennial alternative in the same family: leaves are cut for use and the bulb is left in the ground to keep producing, rather than the whole plant being pulled. They appear among the perennial vegetables (Garden Organic). Check the variety, since some sold as bunching onions, such as Performer, are annuals that can't be grown as bulbs.

Common problems

• Slugs and snails are the main risk to young seedlings, particularly in a wet spring.
• Onion downy mildew damages foliage and bulbs and is encouraged by overcrowding. Thin seedlings properly rather than leaving a dense row.
• Onion fly maggots damage roots and bulbs and can kill seedlings outright. Fine mesh or fleece from sowing is the dependable defence rather than a companion plant.

Common questions

Sources