Yellow onions are the workhorse of the kitchen — the all-purpose onion for cooking, the one that stores longest, and the easiest of the three onion colours to keep through winter. In Zone 8's mild climate they are a reliable crop: plant in late winter, harvest in early summer, cure in the sun, and you can be eating your own onions for months. This guide sets out when to plant yellow onions in Zone 8 and how to grow bulbs that actually keep.
Zone 8 at a glance
Zone 8 covers parts of the southern United States, the Pacific Northwest coast and parts of California, where average winter lows run 10 to 20°F. The average last spring frost falls Mar 1–15 and the average first autumn frost Nov 15–Dec 1. Those are USDA zone averages drawn from NOAA frost records, not exact dates for any one garden — frost dates vary by microclimate, elevation and year, so always check your local extension service and the forecast before planting. Use the frost date calculator for your own averages, and browse the planting calendar hub for the full Zone 8 year.
When to plant yellow onions in Zone 8
| Step | Timing in Zone 8 |
|---|---|
| Start indoors | January, 8 to 10 weeks before transplanting |
| Transplant outdoors | February to March, once soil can be worked |
| Plant sets outdoors | February to March |
| Autumn sowing (mild spots) | October to November, for overwintering |
| Harvest | June to July, when tops fall over |
Yellow onions are hardy, so frost is not the limiting factor — day length is. Bulbing starts as days lengthen in late spring, and only plants that are already a good size will form large bulbs. That is why February to March planting, in the Zone 8 February guide window, matters more than any other single decision. Use the seed starting calculator to work out dates for your own garden.
How to start yellow onions
Sow seed indoors in January, thinly in trays of seed compost, and keep it moist until germination in 7–14 days. Strong light keeps seedlings stocky; trim the tops to about 4 inches if they grow leggy. Harden off for a week, then transplant in February to March. Sets are simpler and very reliable in Zone 8: push each set into the soil so the tip just shows, and it will root away in the mild late-winter soil.
Soil, spacing and sun
Yellow onions need full sun and loose, fertile soil that drains well. On clay, build a raised bed and fork in compost — waterlogged soil rots bulbs and invites disease. They like a soil pH of 6.0–7.0. Plant shallowly, bulbs at the surface, spaced 4–6 inches apart in rows a foot apart. Keep the bed weed-free: onions are shallow-rooted and poor competitors, and weeds will halve your harvest if left alone.
| Fact | Range |
|---|---|
| Sun | full sun |
| Days to germination | 7–14 |
| Days to maturity | 90–120 |
| Spacing | 4–6 in |
| Soil pH | 6.0–7.0 |
| Sowing method | both |
| Cold tolerance | hardy |
All figures are broad published ranges from standard horticultural references, and they vary by variety, soil and weather. Check your local extension service for advice on your own garden.
Watering and feeding
Water moderately and evenly while bulbs are swelling in spring — a deep soak once or twice a week is far better than a daily sprinkle. As soon as the tops yellow and fall, stop watering altogether so the bulbs dry and cure. Straw mulch holds spring moisture, but pull it away from the necks as harvest nears.
Companion planting
Marigolds, basil and lettuce are good companions, sharing the bed without crowding the onions. Onions also protect carrots: their smell confuses carrot rust fly. Avoid planting beside peas and beans, which are unhappy next to alliums, and give onions their own bed or row rather than squeezing them between hungry crops. The companions listed for yellow onions in standard references are marigolds, basil, onions, lettuce.
Pests and problems
Aphids on the leaves, slugs in wet weather and cutworms at soil level are the usual pests. Wash aphids off with water, use card collars against cutworms, and keep the bed clear of debris where slugs hide. The disease to respect is white rot, which lingers in soil for years — if your ground has had it, grow onions in a new bed or in containers. The pests most often listed for yellow onions are aphids, slugs, cutworms. Inspect plants weekly, act early while numbers are small, and encourage natural predators such as ladybirds and hoverflies.
Harvest and storage
Harvest in June to July when the tops have yellowed and flopped. Lift with a fork on a dry day and cure the bulbs in the sun for one to two weeks, turning once, until the necks are dry and papery. Then trim the tops to about an inch, rub off loose skins, and store in a cool, dry, airy place — a mesh bag, a braid or a slatted crate. Well-cured yellow onions are the best keepers of all, lasting for months.
Frequently asked questions
When should I plant yellow onions in Zone 8?
Transplant seedlings or plant sets in February to March, before the average last frost of Mar 1–15. In mild spots, October to November sowing can overwinter. Early planting is essential for large bulbs.
How long do yellow onions store?
Properly cured and stored cool, dry and airy, yellow onions keep for months — longer than red or white onions. Check the store regularly and use any soft or sprouting bulbs first.
Seed or sets for yellow onions?
Sets are easiest and very reliable; seed gives more variety choice and cheaper plants. Both work well in Zone 8 if planted early. Seed needs starting indoors in January.
Why are my onion tops falling over early?
Tops falling over in June or July is normal — it means the bulbs are finishing. Tops falling in spring usually means damage from cutworms, drought or disease. Lift and check a bulb before assuming the crop is ready.
For the full year, browse the planting calendar hub. Compare with Yellow Onions in Zone 7, and see also Red Onions in Zone 8.