White onions are the mild, crisp onions of Mexican and southwestern cooking — sweeter and less pungent than yellow onions, with a clean white flesh that stays crisp in salsas, salads and fresh dishes. They are the onion to grow if you eat onions fresh rather than storing them: their flavour is at its best within weeks of harvest, and they are superb pickled whole.
White onions grow exactly like other onions and take 90–120 days to mature, but they have one honest drawback: they do not store well. Thin skins and high water content mean they keep for weeks to a couple of months, not all winter. Grow them for the summer kitchen, not the winter store, and this guide will show you how — from sets or seed, through feeding and watering, to curing and using them while they are at their best.
White 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
White 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.
White onions can be started from seed indoors, sown directly, or grown from sets. Sets are the simplest: push small bulbs into prepared soil in early spring so just the tip shows, and they will root quickly.
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
White 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.
White onions want fertile, loose, well-drained soil with a pH of 6.0–7.0. Dig in compost before planting and feed lightly while the leaves are growing — the bulb can only be as big as the leafy top that feeds it.
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 White 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 White 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 White 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
White onions are ready about 90–120 days after sowing, when the tops yellow and flop over — that is the harvest signal. Stop watering, leave the bulbs in the ground for a few days to start drying, then lift them carefully with a fork on a dry day. Cure them in a single layer in a warm, airy spot out of direct sun for two to three weeks, until the necks are dry and the skins papery.
White onions are best used fresh, and that is how to plan for them: eat them within weeks to a couple of months of harvest, and do not expect them to last the winter. Store cured bulbs in a cool, dry, airy place in a mesh bag, and use any with thick or soft necks first — they will not keep. Small white onions are excellent pickled whole, and any surplus can be chopped and frozen for cooking.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Bulbs stay small | planted too late, crowded, or dry while swelling | Plant early, space 4–6 inches apart, and water steadily. |
| Plants bolt and flower | cold shock in spring | Do not plant out too early; use heat-treated sets. |
| Bulbs rot in storage | cured too little, or watered too late | Cure fully until necks are dry; stop watering when tops fall. |
Bulbs stay small
Likely cause: planted too late, crowded, or dry while swelling. Small bulbs are usually a timing problem: onions planted late never grow enough leaf before bulbing, and crowded or weedy beds starve the plants. Keep the bed weed-free, thin to the right spacing, water while bulbs are swelling, and check that you are growing a day-length type suited to your latitude.
Plants bolt and flower
Likely cause: cold shock in spring. Bolting happens when young onions are chilled — a cold snap after planting triggers flowering instead of bulbing. Bolted plants will not bulb properly, so use them as green onions.
Bulbs rot in storage
Likely cause: cured too little, or watered too late. White onions rot in storage if they were not cured properly or were watered after the tops fell. Cure for a full two to three weeks in warm, dry air until the neck is completely dry and papery, and store only sound bulbs in an airy place.
Frequently asked questions
How long do white onions take to grow?
White onions take 90–120 days from sowing to harvest. Sets are faster than seed.
How long do white onions keep?
Not long — a few weeks to a couple of months, even when well cured. White onions have thin skins and high water content, so they are a fresh-eating onion, not a storage onion.
What are white onions best used for?
Fresh dishes: salsas, salads, sandwiches, Mexican and southwestern cooking, and pickling whole. Their flavour is milder and sweeter than a yellow onion, and they stay crisp raw.
Can white onions be grown from seed?
Yes — start seed indoors and transplant out, or sow directly in early spring. Germination takes 7–14 days.