Plant onion starts in November or December, and you'll be pulling onions from late spring into summer. Onions aren't California natives, but they fit into a California native garden better than you might expect. They grow through our wet winter and finish up just as native plants settle into their dry summer rhythm.

Our annual batch of onion starts (also called transplants or seedlings) has arrived at Evergreen Nursery. They're already past the fussy germination stage, so you tuck them in, keep them watered, and let the mild East Bay winter do the work. The one catch is that they come in bunches of 30, so we've included plenty of ways to make room.

Key Takeaways

• Plant onion starts in November and December for a late spring and summer harvest.

• This year's varieties are 'Yellow Merlin', 'Betty White', 'Red Berger', 'Walla Walla Sweet', and the red torpedo 'Florence'.

• Mixing varieties spreads out your harvest, because each one starts forming bulbs at a different day length.

• Thirty onions fit in about 3½ square feet at 4-inch spacing.

• Onions need full sun, loose soil, steady moisture, and early feeding.

Why Onions Pair Well With a California Native Garden

Most California native plants want little to no water once summer arrives. Onions want steady moisture from planting through spring. That sounds like a conflict, but the calendar solves it. Onions go in during November and December, ride out the rainy season, and come out before the dry months begin.

A few habits keep both sides happy:

• Give onions their own bed or container next to your native plantings, not in the middle of them. That way, any extra watering your vegetables need never lands on plants that prefer to stay dry.

• Let winter rain do most of the work. Check the soil before you water, and you'll rarely need to do much.

• Plant blooming natives nearby. A mix of flowering natives brings beneficial insects through the garden, and your veggie bed benefits too.

Still building out your native plantings? Browse our California native plants while you're picking up your onion starts.

Meet This Year's Onion Starts

Here's the one bit of onion science worth knowing: a young onion spends its first months growing leaves, then switches to building a bulb once days get long enough. Short-day onions start bulbing at about 10 to 12 hours of daylight, intermediate-day onions at 12 to 14 hours, and long-day onions at 14 hours or more.

That's why fall planting pays off. The more leaves an onion grows over winter, the bigger the bulb it can build in spring. The UC Master Gardeners of Santa Clara County note that the Bay Area sits on the edge between long-day and short-day regions, so all three types can succeed here.

• 'Yellow Merlin' (short-day): A firm, uniform yellow globe and a dependable all-purpose kitchen onion. Well-cured bulbs store nicely.

• 'Betty White' (short-day): Bright white bulbs for salsas, sandwiches, and quick sautés. It matures early.

• 'Red Berger' (intermediate-day): An easy red onion recommended for our region. Great sliced raw on burgers.

• 'Walla Walla Sweet' (long-day): The famously mild, juicy sweet onion. UC Master Gardeners note it matures early enough to do well here. Eat it fresh, since sweet onions don't store well.

• 'Florence' (intermediate-day): An Italian heirloom with long, torpedo-shaped, red-purple bulbs and a mild, sweet flavor. Slice it into salads or roast it whole.

Because each variety hits its day-length trigger at a different time, they won't all mature at once. The short-day types usually finish first, so you'll harvest in waves.

How to Fit 30 Onion Seedlings in a Small Garden

Onions are skinny, upright, and polite about sharing space, which makes a full bunch easier to place than you'd think.

Plant a compact block. Skip the rows and plant in a grid with 4 inches between seedlings in every direction. That's 9 onions per square foot, so 30 fit in about 3½ square feet, roughly the size of a welcome mat. UC Master Gardeners recommend 4 to 6 inches for bulb onions, so go wider if you want bigger bulbs.

Plant tight and harvest scallions along the way. Set starts 2 to 3 inches apart, the spacing UC Master Gardeners suggest for green onions. Through winter, pull every other plant as a scallion and leave the rest at 4 to 6 inches to bulb up. Two harvests, one bunch.

Tuck onions along the edges. A line of onions makes a tidy border for a raised bed or walkway. Just keep weeds in check, because onions hate competition.

Try a container. Any pot at least 12 inches deep with good drainage works, and a half wine barrel holds plenty of starts. For large planters, buying potting soil in bulk stretches your budget. Our Bulk Happy Hippie Planting Mix is made for edibles and favored by our local veggie-growing friends at Tandi Family Farms. Set the container in full sun and feed monthly with a liquid organic fertilizer.

Still out of room? Split your bunch with a neighbor. Everybody wins.

When and How to Plant Onion Starts

UC Master Gardeners recommend transplanting onion seedlings in November and December, soon after you bring them home so the roots don't dry out. Choose a spot with at least 6 hours of direct sun.

Onions want loose, well-draining soil. If you're working with heavy East Bay clay, mix in E.B. Stone Pumice for aeration and E.B. Stone Soil Booster for structure. Set each start so the white base sits just below the surface. Planting too deep slows bulb formation.

Feeding: Mix a balanced organic fertilizer like E.B. Stone Sure Start 4-6-2 into the planting area, then side-dress with a vegetable fertilizer or liquid drench every 3 to 4 weeks through early spring. If you're growing 'Walla Walla Sweet', UC Master Gardeners suggest skipping fertilizers that contain sulfur.

Watering and mulching: Onion roots are shallow, so keep soil evenly moist but never soggy. A light mulch of straw, shredded leaves, or compost holds moisture and suppresses weeds.

Pro tip: Consistent moisture is your best defense against bolting. An onion that's been under-watered or hit with days of heat will often send up a flower stalk instead of sizing up its bulb.

Pests: Watch for thrips, tiny insects that leave silvery streaks on leaves. A strong spray of water or insecticidal soap usually handles them. Don't plant where garlic, leeks, or other alliums grew last year. Rotate to a new spot.

Read More: How To Grow Onion Transplants in Your East Bay Garden

Harvesting and Storing Onions

Onions are nearly ready when the tops yellow and flop over. At that point, stop fertilizing and cut back on water so the bulbs don't turn mushy. Pull or gently dig the mature onions, then cure them on racks in a warm, dry, shady, well-ventilated spot for about two weeks before trimming.

Eat 'Walla Walla Sweet' and 'Florence' fresh, and save storage types like 'Yellow Merlin' for the pantry.

Onion Starts FAQ

How many onion starts come in a bunch?

Each bunch at Evergreen Nursery holds 30 seedlings of a single variety.

When should I plant onion starts in the East Bay?

November and December are ideal. Plant soon after purchase so the roots don't dry out.

Can I grow onions in a California native garden?

Yes, with one adjustment. Give onions their own bed or container beside your natives, so their winter and spring watering doesn't reach plants that prefer dry summers. Onions come out by early summer, right when natives want to stay dry.

How far apart should I plant onion starts?

Plant bulb onions 4 to 6 inches apart. For green onions, 2 to 3 inches works.

Can I grow onions in containers?

Yes. Use a container at least 12 inches deep with drainage holes, a good potting mix, and full sun.

Why are my onions flowering instead of forming bulbs?

That's bolting, often triggered by irregular watering or temperature swings. Bolted onions are still edible, so pull them and use them right away.