The Gappy Row: A November Audit of Overwintering Onions

Overwintering onions are one of the quiet bargains of the veg plot. You push a few dozen little brown sets into the ground in autumn, ignore them through the worst of the weather, and then watch them bulk up in late spring. At least, that’s the theory. By mid-November, a row that looked neat a few weeks ago can resemble a bad game of dominoes: one set sitting proud, another vanished, a third slumped over like it’s had a long lunch.

The good news is that most November gaps are not a mystery. They are usually one of four things — birds, loose soil, wet ground or dodgy sets — and three of those are fixable in about ten minutes with a trowel, a handful of soil and a bit of netting. As of this week in November 2026, it’s worth walking the row properly rather than hoping the problem sorts itself out.

First, read the gaps

Don’t just count the missing onions. Look at what is left around them. A set that has been tugged out and left on the surface usually has a clean, dry base and maybe a few white roots showing. That is classic bird damage — blackbirds, pigeons and the occasional crow will pull at freshly planted sets, especially if the soil is loose and the tip is sitting proud. They are not eating the onion itself so much as investigating a handy little bulb-shaped thing, but the result is the same: a set left high and dry, or simply gone.

If the set is still in place but sitting on a little mound of soil, frost heave or heavy rain is the likely culprit. Onion sets need firm ground. If you tucked them into fluffy autumn soil, a wet spell followed by a cold snap can lift them like a cork. The same goes for sets planted into a dip or a low corner that holds water. On clay soil, a winter puddle is less a puddle and more a slow execution. Affected sets go grey, soft and sour-smelling, and there is no rescue for those.

Then there is the set itself. Small, dry, firm bulbs are what you want. Large sets can bolt in spring, and soft or mouldy ones were never going to last the winter. If a supplier sent you sets that were already sweating in the bag, some losses are not your fault. That said, a surprising number of “failures” are just sets that were never firmed in properly in the first place.

The ten-minute rescue walk

Go out when the soil has drained a little — not while it is sticky enough to weld to your boots. Take a trowel, a small bag of compost or sieved soil, and a pair of gloves. Work along the row set by set. If a bulb is loose, lift it and look at the base. Firm and dry? Replant it. Soft, mushy or smelling off? Bin it, and don’t put it on the compost heap if it is clearly rotting.

Replant at the right depth: the tip should sit just at or slightly below the soil surface, not buried like a tulip and not perched on top like a gargoyle. Use a trowel rather than a dibber if your soil is heavy. A dibber can leave a smooth air pocket that the roots struggle to fill. Make a small hole, drop the set in, then firm the soil around it with your fingers and finish with the flat of your knuckles. You want the set held snugly, not cemented in. If the ground is very wet, stand on a board while you work to avoid compacting the bed.

While you are there, fill any genuine gaps if you still have spare sets. In early November there is just about time for another push, though don’t force it if the soil is cold and sodden. A set planted into a swamp is a donation to the rot. If the gap is in a low, wet corner, leave it empty and consider a raised ridge or a different crop next year.

Net now, not after the pigeons learn

Netting is the single most useful bit of kit for overwintering onions. Use hoops or short canes to hold bird netting clear of the tips, then peg the edges down firmly. Loose netting is worse than none — birds can get tangled, and a flapping edge just invites cats and foxes to investigate. Check the net after gales, because a blown-back corner is an open invitation.

Fleece can work as a physical barrier too, but it tends to flatten the tips and trap damp. Netting is usually the better choice unless you are also trying to keep off hard frost. Either way, the routine is the same: firm the set, cover the row, check it after weather.

Choose sets that expect a British winter

If you are buying more sets — or planning for next autumn — look for named overwintering varieties rather than a loose handful from the back of a shed. Radar, Electric and Senshyu are the sort of reliable types worth asking for. Red Winter is good if you want a red onion, though it can be a little less robust in a wet year. Buy from a reputable supplier, choose medium-sized firm sets, and plant them within a few days of arrival. If you can only get large, soft sets, expect a higher failure rate and plant a few extras.

What success actually looks like

A perfect row is not the goal. Overwintering onions always lose a few, and a 10–20% gap is not a disaster. What you are trying to avoid is the slow unravelling that comes from loose sets, wet feet and birds working the row every morning. Firm them in, net them down, and then leave them alone apart from the odd weed and a check after rough weather.

Come June, those modest little sets should be proper bulbs, ready to lift and dry. The row may still have a gap or two, but it will have earned its space. And next autumn, you’ll know exactly which corner of the plot to avoid planting with onions.