October is one of the most satisfying months on a UK allotment. Summer crops are coming out of the ground, but that does not mean every vegetable bed needs to stand empty. Planting autumn onion sets and garlic now allows their roots to establish in cool soil before winter, giving the plants a useful head start when growth resumes in spring. The two crops look similar when they are planted, yet their requirements are not identical. Understanding those differences prevents many of the common mistakes.

This guide explains which planting material to buy, how to prepare a bed, the depth and spacing to use, and what to watch for through a wet British winter. It also covers container growing, watering, feeding and harvesting. The aim is simple: healthy plants, good drainage, and realistic expectations for what an October planting can achieve.

Choosing the right onion sets and garlic

Autumn onion sets are small immature onions supplied specifically for planting in autumn. Look for varieties marketed as overwintering, rather than assuming that any packet of spring onion sets will survive the same conditions. Common autumn choices include Senshyu-type onions and other winter-hardy selections. Check the packet instructions because suitability, harvest timing and resistance to bolting vary between varieties. Avoid oversized sets where possible: large sets can be more prone to producing flower stalks after cold weather. Small, firm sets without mould or soft areas are a better starting point.

Garlic should ideally be supplied for planting, not taken from a supermarket food bulb. Planting stock is selected and sold as suitable for growing and is less likely to bring in problems associated with unknown stock. Hardneck garlic often benefits from a substantial cold period and generally produces a central flower stalk called a scape. Softneck types tend to store for longer and usually produce more cloves of different sizes. The important detail is to select a variety recommended for the UK and plant individual, undamaged cloves with their papery skins intact.

Understanding the difference between autumn onions and garlic

An onion set is planted whole and grows into one larger onion. Garlic is planted as individual cloves, each of which develops into a new bulb containing several cloves. Both need plenty of daylight and open ground, but garlic has a particularly strong need for cold exposure to divide properly into a bulb. October planting often supplies that exposure naturally. Onions can be affected by winter waterlogging and later bolting, especially where sets are large, plants are stressed or temperatures fluctuate sharply.

Neither crop is normally harvested during winter. Autumn onions are often ready in late spring or early summer, depending on the variety and conditions, while autumn-planted garlic is commonly lifted in summer. Exact harvest dates change with the weather. Do not plant autumn sets expecting a quick supply of full-sized onions by Christmas. For winter kitchen use, it is usually better to rely on onions and garlic harvested and stored earlier in the year.

Pick a sunny, well-drained growing position

Both crops grow best in open light with fertile, free-draining soil. A site that spends winter under standing water is a poor choice, even if the soil looks rich during summer. Onion roots require oxygen; prolonged waterlogging can lead to rotting sets, patchy growth and fungal trouble. In heavy clay, work on the soil structure over time with mature organic matter, and consider a raised bed if drainage remains unreliable. Do not try to rescue a soaking bed by digging or treading on it while it is wet, as this can damage the structure.

Avoid planting alliums in the same patch year after year. Rotating them with unrelated vegetables can help reduce the build-up of some soil-borne problems. If a bed has recently suffered severe white rot, moving onion and garlic crops elsewhere is especially important: there is no simple home-garden cure for infected soil. Keep the chosen spot clear of perennial weeds before planting because removing couch grass or bindweed from among established onion leaves is difficult without disturbing the shallow roots.

Prepare the soil before planting

Begin by removing exhausted crops, weeds and substantial plant debris. Fork over the ground lightly only when it is workable; there is no need to pulverise it into a fine powder. Incorporate well-rotted garden compost if the bed needs improving, preferably in advance of planting. Fresh manure immediately underneath sets and cloves can encourage problems and is best avoided. Aim for a reasonably level surface with a crumbly top few centimetres so each piece of planting material touches soil rather than sitting in an air pocket.

If you have a heavy soil that tends to crust, add compost over several seasons and protect bare patches with organic mulch between crops. Autumn planting is not about feeding as heavily as possible in October. Roots need somewhere hospitable to grow, but lush, soft green leaves produced by excessive nitrogen can be vulnerable during cold spells. A soil that has been improved steadily is generally better than one given a last-minute application of strong fertiliser.

Plant autumn onion sets at the right depth

Make shallow holes or a narrow drill and position each set with the pointed end facing upwards and the flatter root plate downwards. A common spacing is approximately 10–15 cm between sets and 25–30 cm between rows, although closely planted rows can work in a carefully managed raised bed. Set the bulbs so the tips are at or just above the soil surface unless your chosen product advises otherwise. Push soil around each set firmly enough to remove obvious gaps without compacting the whole bed.

Birds sometimes pull fresh onion sets out of the ground, particularly when the soil is loose and the shoots are not yet rooted. If sets appear scattered across the bed, replant them promptly. A temporarily secured mesh or fleece cover, raised so that birds cannot tug through it, can prevent repeated damage. Do not simply plant sets much deeper to hide them, because burying the necks heavily can make establishment less reliable. Check the bed after windy and frosty weather.

Plant garlic cloves separately and slightly deeper

Break garlic bulbs into cloves only when you are ready to plant. Choose sound, plump cloves and discard any that are soft, spotted or mouldy. Place each clove with the pointed end upwards and the flat basal plate downwards. In many UK gardens, a useful starting depth is around 5 cm of soil over the top of the clove; adjust for local conditions and the advice for the variety. Space cloves roughly 10–15 cm apart, allowing around 25–30 cm between rows. Give vigorous large-bulbed varieties a little extra room.

Garlic planted too shallowly may be lifted by frost heave, and cloves planted in waterlogged ground may rot before they establish. Mark the rows because emerging shoots can look like grass at first glance. If a clove starts to push above the soil after a hard frost, firm soil gently back around it on a frost-free day. A light protective mulch may moderate soil temperature, but avoid piling thick wet material directly onto the shoots or creating a constantly soggy surface.

Watering and feeding through autumn and winter

Water lightly after planting only if the soil is dry. In a typical UK October, rainfall is often sufficient once the roots are established. During winter, the greater risk is frequently too much moisture rather than too little. Probe the ground or compost with a finger instead of watering by routine. In containers, pay extra attention during extended dry periods when roofs or walls prevent rain reaching the soil. Never leave the pots soaking in trays of water.

There is little need to force vigorous top growth with nitrogen-rich feeds in autumn. When growth resumes in late winter or early spring, a balanced, modest feed may help on poor soil, but follow product directions and assess how the plants look first. Avoid overfeeding later in the season, which can encourage leaf growth at the expense of mature bulbs. Stop treating the crop like a leafy vegetable as the bulbs approach harvest. Good soil health, light and steady moisture matter more than frequent feeding.

Protecting plants from common winter problems

Birds, slugs and poorly draining soil can all affect autumn plantings. Inspect for missing sets, grazed shoots and rotting cloves rather than assuming every gap is caused by frost. Fine mesh can deter birds, but it needs to be supported and checked so leaves do not become caught. In mild damp spells, slugs may eat young growth; remove hiding places near the bed and use appropriate controls where needed. A cold snap is rarely the only problem. Repeated wetness followed by freezing can be more damaging to fragile roots.

If some leaves yellow during winter, look at the whole plant before intervening. A few older leaves dying back is different from a collapsing stem or mushy base. Pull and dispose of clearly rotting plants rather than leaving them to infect the immediate area. Keep beds weeded and avoid walking on wet soil. If you suspect onion white rot because of white fungal growth and small black resting bodies at the base, do not compost affected bulbs and avoid replanting alliums in that ground.

When and how to harvest

Autumn onions are generally ready once bulbs reach a useful size and tops begin to soften, bend and dry naturally. They are often harvested earlier than spring-planted onions and may not keep quite as long. Lift them carefully in suitable dry weather. Allow the necks and outer skins to dry somewhere ventilated and sheltered, then check each bulb for damage before storing. Bulbs with thick, soft necks should be used first, because they are less reliable in storage.

Garlic is usually ready when several lower leaves have browned but upper leaves still retain some green. Do not leave bulbs so long that all wrappers disintegrate in the ground. Lift with a fork placed away from the bulb and handle gently to avoid bruising. Cure under cover in a dry airy place, out of harsh sunshine, before trimming or storing. Never judge harvest readiness from the calendar alone: a cool northern season, exposed allotment or different variety may shift the timing significantly.

Frequently asked questions

Is October too late to plant garlic? No. October is a common planting time for UK garlic, though the ideal window varies by variety and local conditions. Some varieties can be planted later in autumn or winter.

Should I soak onion sets before planting? It is usually unnecessary. Plant clean, firm sets directly into suitable soil and avoid leaving them wet for long periods.

Can I plant garlic and onion sets together? They can share a growing area if spacing and crop care are suitable, but keeping separate clearly labelled rows makes planting depth, harvesting and rotation easier.

Should I put chicken manure pellets in each planting hole? No. Concentrated fertiliser close to young roots is not a substitute for good soil preparation; apply fertiliser only where needed and according to the product label.

What if the tops grow before winter? Green shoots in autumn are normal. Hardy varieties usually tolerate typical winter weather if their roots remain healthy and the ground drains well.

A final word from Gardening with Ben

October planting is a small job with a long reward. Give autumn onion sets and garlic their own properly spaced rows, protect the soil from becoming saturated and keep an eye on them through the darker months. You do not need a perfect allotment or expensive equipment: a sunny bed, the right planting stock and a few regular checks will take you a long way. Keep smiling, keep shining, keep gardening with Ben.