Yellow onions are the workhorse of the kitchen garden — the all-purpose onion for cooking, the one that stores all winter, and the one every gardener should grow first. Their flavour is strong when raw and sweet when cooked, their skins are thick and papery, and a well-cured yellow onion will keep in a cool, dry place for months after harvest. No other onion earns its space quite so well.
Yellow onions take 90–120 days to mature, and the crop is won or lost in the details: planting early, feeding while the leaves grow, stopping feed and water at the right moment, and curing properly. Get those right and you will have onions until spring. This guide covers the full cycle — sets or seed, spacing, day length, and the curing and storage that make yellow onions the winter keeper.
Yellow Onions at a glance
| Growing factor | What this crop needs |
|---|---|
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Days to germination | 7–14 |
| Days to maturity | 90–120 |
| Spacing | 4–6 inches |
| Water needs | moderate |
| Cold tolerance | hardy |
| Family | Amaryllidaceae |
Starting seeds
Yellow Onions can be started indoors or sown directly, and which you choose depends on your season. Indoor sowing gives you a head start in cold zones; direct sowing is simpler and avoids transplant shock. Either way, germination takes 7–14 days in warm, moist soil. Our seed-starting calculator can work out indoor sowing dates, and the seed-spacing calculator works out how many seeds you need for your bed.
This is a hardy crop, so it suits the cool parts of the year: in Zones 3–5 sow in early spring and again in late summer; in Zones 6–8 spring and autumn sowings do well, with summer sowings struggling in heat; in Zones 9–10 sow through autumn, winter and early spring; and in Zones 11–13, which are frost-free, grow it in the cooler months with afternoon shade. Check your dates with our frost-date calculator or the last-first frost lookup — and when in doubt, ask your local extension service.
Yellow onions grow from seed, transplants or sets, and sets are the easiest start: push small bulbs into the soil in early spring with just the tip showing. From seed, start indoors and transplant out as thin seedlings, or sow directly; germination takes 7–14 days.
Transplanting and planting out
Harden seedlings off for a week before planting out: put them outside for a few hours a day, increasing the time and exposure, and bring them back in at night. Plant out at the final spacing of 4–6 inches apart, in holes the same depth as the pot. Water each plant in well and mulch around (not against) the stems to hold moisture. Our plant-spacing calculator shows how many plants fit your bed at 4–6-inch spacing.
Soil and feeding
Yellow Onions grows best in soil with a pH of 6.0–7.0, so test your soil before you plant — a cheap test kit tells you more than guessing ever will. Work in plenty of compost or well-rotted manure to improve structure and feed the soil life, and make sure the bed drains freely. Our soil-volume calculator and raised-bed soil calculator work out how much soil or compost your bed needs.
Feed generously through the season: work compost into the bed before planting and side-dress with a balanced fertiliser once plants are growing strongly. Hungry fruiting and leafy crops repay feeding with visibly bigger harvests, but too much nitrogen gives leaf at the expense of fruit, so follow the label. Our fertiliser calculator works out how much to apply.
Yellow onions need fertile, well-drained soil at pH 6.0–7.0, and they are hungry while growing leaves. Dig in compost before planting, feed lightly in spring, and then stop all feeding once the bulbs begin to swell — late nitrogen makes soft bulbs that rot in store.
Watering
Water evenly and avoid letting the soil swing between soaked and bone dry. A deep soak once or twice a week beats a daily sprinkle, because it encourages roots to grow down where the soil stays cooler and moister. Mulch helps enormously here, holding moisture and keeping the soil temperature steady. Our watering calculator gives a starting point for your bed size and soil, and the watering schedule generator can build a routine around it.
Sunlight and temperature
Give Yellow Onions full sun — at least six hours of direct sun a day, and more is better in most zones. Sun drives flavour and yield in this crop, and plants in shade stay leggy and unproductive. Our sunlight calculator can check whether your spot gets enough sun.
It is hardy and copes with cool weather and light frost, which makes it a spring and autumn crop in most zones. What it dislikes is heat: hot weather pushes it to bolt and turns leaves bitter, so in warm zones grow it in the cool season and give it afternoon shade.
Pests and diseases
The pests and diseases to watch for with Yellow Onions are aphids, slugs and cutworms.
Aphids cluster on tender new growth and under leaves, sucking sap and leaving sticky honeydew.
Slugs and snails chew ragged holes in leaves at night and love damp, mulched beds.
Cutworms chew through young stems at soil level overnight.
Prevention beats cure: rotate crops so the same family does not grow in the same bed year after year, clear debris at the end of the season, and inspect the undersides of leaves weekly. Our pest identifier helper can help you name a pest from its damage, and the plant-disease checker can narrow down a leaf problem.
Companion plants
Good companions for Yellow Onions are marigolds, basil, onions and lettuce.
Marigolds are the classic companion: their roots and scent deter several soil pests, and their flowers bring in pollinators and beneficial insects.
Basil is said to improve the flavour of its neighbours and its scent confuses some pests; it also makes good use of the same sunny, well-watered bed.
Onions help mask the scent of their neighbours from pests, and their upright leaves take little light from the plants beside them.
Lettuce is a shallow-rooted, quick crop that fills the gaps between taller plants without competing hard for nutrients.
Plant companions in the same bed rather than in a separate corner — that is how they do their work. Our companion-planting finder can suggest more pairings for your bed.
Harvesting
Yellow onions are ready about 90–120 days after sowing, when the tops yellow and fall over of their own accord. That is the signal to stop watering and let the bulbs dry in the ground for a week. Then lift them on a dry day with a fork, being careful not to bruise or cut them — damaged bulbs rot in store. Lay them in a single layer in a warm, airy place out of direct sun to cure for two to three weeks, until the necks are dry and tight and the skins rustle.
Once cured, trim the tops to an inch or two and store the bulbs in a cool, dry, airy place — a mesh bag, an old pair of tights, or a slatted tray, never a sealed bag. A well-cured yellow onion keeps for months, often until spring. Check the store monthly and use any soft bulbs first. Braiding the tops of fully cured onions is traditional and practical: it keeps them aired and easy to reach.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Bulbs stay small | planted too late, crowded, or the wrong day-length type | Plant early, space 4–6 inches apart, and choose a type suited to your latitude. |
| Tops bolt and flower | cold shock after planting | Plant sets once soil has warmed; use heat-treated sets. |
| Bulbs rot in storage | not cured fully, or watered too late | Cure for two to three weeks until necks are dry; stop watering when tops fall. |
Bulbs stay small
Likely cause: planted too late, crowded, or the wrong day-length type. Small bulbs usually mean the plant never grew enough leaf before bulbing started — planted too late, crowded, weedy, or dry while growing. The other classic cause is day length: a short-day onion grown in the north bulbs before it has grown, and a long-day onion in the south never bulbs at all.
Tops bolt and flower
Likely cause: cold shock after planting. Bolting follows a cold snap in spring: the young plant thinks it has had winter and flowers instead of bulbing. Bolted plants will not store, so pull and use them fresh.
Bulbs rot in storage
Likely cause: not cured fully, or watered too late. Rot in store almost always means the bulbs went in damp — not cured long enough, or watered after the tops fell. Cure until the neck is completely dry and papery, store only sound bulbs in an airy place, and check the store monthly for soft ones.
Frequently asked questions
How long do yellow onions take to grow?
Yellow onions take 90–120 days from sowing to harvest. Sets are quicker than seed.
How long do yellow onions keep?
A well-cured yellow onion keeps for months — often six to eight months — in a cool, dry, airy place. They are the best storing onion by far.
Should I grow yellow onions from seed or sets?
Sets are easiest and most reliable for a first crop. Seed is cheaper and gives more varieties, including the best storage types, but needs starting indoors or careful direct sowing.
When should I stop watering onions?
Stop watering once the tops start to yellow and fall over. The bulbs need a dry finish to cure and store well — watering after that point makes soft bulbs that rot.