Best Onion Varieties for Scotland

An autumn-planted set spends the winter doing nothing visible, then swells into a bulb ready to lift in June or July. A spring-planted set of the same variety, planted five or six months later, isn't ready until July at the earliest and often not until autumn. That's a two-month head start for the price of choosing a planting date over a planting season, and in a growing season that's already shorter than most of the UK's, two months is worth having.

The gap: which AGM variety is actually an autumn set

Six varieties are recommended: Centurion, Red Baron, Hercules, Sturon, Rumba, and Marshalls Red Fen (five hold the Award of Garden Merit; Marshalls Red Fen does not).

That list doesn't settle which of the six are actually suitable for autumn planting. AGM is a UK-wide horticultural award, not a Scotland-specific recommendation, and it says nothing about whether a variety was bred to sit through a winter in the ground, and in at least one case, the general growing guide's summary contradicts the more detailed picture below.

The choice matters in Scotland specifically because a cold snap after planting is what triggers boltingA plant switching early into flowering and seed production, usually triggered by stress, after which leaves, roots or bulbs turn bitter or unusable. Full page →, and a late one landing on a young spring-planted set is a real risk against a Scottish spring that arrives later than further south (see the frost dates guide for how much later, by region). An autumn-planted set of the right variety is already established by the time that risk peaks, which is why the variety choice matters, not just the planting date. For the exact autumn planting window and how to protect a newly planted set, see the full growing guide.

What each variety's own listing actually says

Two varieties, then, have a documented autumn set: Sturon and Marshalls Red Fen. Two more, Hercules and Rumba, have instructions that name spring and only spring for planting sets. Centurion and Red Baron are unconfirmed either way: their listings give no planting-time instruction at all, so don't autumn-plant them on the assumption that AGM status implies overwinteringKeeping a plant alive and intact through the cold months, whether left outdoors, moved under cover, or stored dormant. Full definition → suitability, it doesn't.

Bolting resistance: what actually holds up for Hercules

The growing guide describes Hercules as having "good resistance to bolting". Hercules's own individual listing, though, lists bolting among the diseases and disorders it "may be susceptible to", the same standard list given for every onion variety, and Hercules is spring-only regardless. Sturon's listing lists bolting as a susceptibility too, with no resistance claim attached at all, the variety confirmed here for autumn planting carries no documented bolting-resistance trait of its own. Its lower bolting risk comes from when it's planted rather than from breeding: autumn-planted sets are established plants by the time the coldest part of late winter arrives, and it's a young, recently-planted set's exposure to a cold snap that's identified as the trigger for bolting, the same mechanism that makes a spring-planted set vulnerable.

Site drainage: why autumn planting isn't right for every plot

Confirming an autumn set for Sturon doesn't mean every garden should use it. Autumn-planted sets sit through winter on ground that has to drain, since a set that stands in cold, waterlogged soil for months rots rather than roots. Heavy, slow-draining clay that sits wet all winter is a real reason to plant Sturon in spring instead and skip the autumn option even though the variety supports it. Raised beds or a bed worked with grit or compost are the safer autumn site on heavier ground.

Heat treatment is a separate consideration and only applies to spring planting. Heat-treated sets are recommended for a spring crop specifically because the treatment reduces bolting risk, it isn't a factor for autumn-planted sets, since these are chosen for autumn use by variety, not by treatment.

Hercules and Rumba, both spring-only, remain reasonable spring alternatives to Sturon, Hercules for a larger bulb, Rumba for its "improved vigour, shape and storage than onion 'Sturon'", but neither variety supports autumn use the way Sturon or Marshalls Red Fen does.

Gardener's World's onion variety coverage doesn't overlap with the AGM six at all, its named varieties are Setton, Hyred and Snowball. It does confirm the general timing principle: onions "sown/planted in autumn spend winter in the ground and are ready to harvest sooner than those sown/planted in spring."

For planting depth, spacing, soil pH, and how to deal with white rot, downy mildew and the general mechanics of bolting, see the full growing guide.

Common questions

Sources