Onion in Zone 7A — Pacific Northwest

Onions are one of the most rewarding crops for Pacific Northwest gardeners, thriving in our mild summers and cool nights while storing beautifully through our wet winters. You'll taste the difference in homegrown onions — they're sharper when fresh, sweeter when cooked, and infinitely more flavorful than anything from the store. Our 183-day growing season gives you plenty of time to grow substantial bulbs, whether you start from seeds, sets, or transplants.

While our cool, slow springs can delay planting and our dry summers require consistent watering, onions are forgiving once established. The key is timing your planting method to work with our climate patterns rather than against them.

Starting onion seeds indoors makes sense if you want the largest possible bulbs or specific varieties not available as sets. You'll need to start seeds in mid-January through early February — about 10 weeks before you can safely transplant outdoors in early April.

Set up seed trays with a good seed-starting mix and keep them warm (65-70°F) until germination. Once seedlings emerge, they need bright light and cooler conditions around 60°F. Bottom watering works best to prevent damping-off disease, which can be a problem during our overcast spring days.

The payoff is impressive — seed-started onions often produce bulbs twice the size of those grown from sets, though they require more attention during our unpredictable spring weather.

You can transplant onion seedlings outdoors from early to late April, once soil temperatures consistently stay above 35°F. Start hardening off your indoor seedlings about a week before transplanting by gradually exposing them to outdoor conditions for longer periods each day.

Space transplants 4-6 inches apart in rows, planting them at the same depth they were growing indoors. Don't worry if they look a bit stressed initially — onions are surprisingly hardy and will recover from our typical spring temperature swings.

Watch for late cold snaps that can still hit us in April. While mature onion plants handle frost well, newly transplanted seedlings benefit from row covers if temperatures drop below 28°F.

Direct sowing works well in our region, especially with onion sets (small bulbs) planted from late March through April. Seeds can go in slightly later, from early April through late June, though later plantings may not develop full-sized bulbs before our first frost in mid-October.

Prepare your soil by working in compost and ensuring good drainage — onions hate wet feet, which can be a challenge during our wet springs. Plant sets pointed-end up, just barely covered with soil, or sow seeds about ¼ inch deep.

The advantage of direct sowing is simplicity, though your bulbs typically won't get as large as those started indoors. Sets are foolproof for beginners and give you a head start on the growing season.

Onions need consistent moisture throughout their growing season but hate waterlogged soil. During our dry summer months, plan to water deeply once or twice per week, providing about 1 inch of water total. Check soil moisture by sticking your finger 2 inches deep — if it's dry, it's time to water.

Water at the base of plants rather than overhead to prevent foliar diseases, though our dry summer air means overhead watering is less risky here than in humid climates. Focus your watering efforts during bulb formation in mid-summer when consistent moisture is crucial for proper development.

As summer progresses and onion tops begin to fall over naturally, gradually reduce watering. Once tops are completely down and yellowing, stop watering entirely — this signals the start of the curing process. Overwatering at this stage can lead to rot and poor storage.

Apply a thin layer of straw or grass clipping mulch around plants to conserve moisture during our dry summer period, but keep it away from the bulbs themselves to prevent rot issues.

Your first onions will be ready for harvest from early July through late October, depending on variety and planting time. Look for the telltale signs: tops falling over and beginning to yellow from the bottom up. This usually happens after about 100 days of growth.

Harvest on a dry day by carefully lifting bulbs with a fork, being careful not to bruise them. Brush off excess soil but don't remove the papery outer layers or trim the tops yet — these protect the bulb during curing.

Cure harvested onions in a warm, dry, well-ventilated area for 2-3 weeks before trimming tops and storing. Our typically dry late summer weather is perfect for outdoor curing on screens or in mesh bags.

As our first frost approaches in mid-October, harvest any remaining onions regardless of size. Smaller bulbs should be used first, while properly cured large onions can store through winter in a cool, dry place.

Onion Thrips These tiny, slender insects cause silvery streaks and stippling on leaves, eventually leading to yellowing and stunted growth. You might see the small, pale insects themselves on close inspection. Thrips thrive in our warm, dry summer conditions and can build up quickly once established. Combat them with beneficial insects like predatory mites, or use insecticidal soap sprays in the evening when temperatures are cooler.

Pink Root This soil-borne fungal disease causes roots to turn pink, then purple, and eventually black and brittle. Plants become stunted and may die in severe cases. Pink root is more common in heavy, poorly-draining soils that stay wet during our spring rains. Improve drainage with raised beds or added organic matter, rotate crops annually, and choose resistant varieties when available.

Bolting Onions send up flower stalks prematurely, making bulbs bitter and reducing storage life. This typically happens when plants experience stress from inconsistent watering during our dry summer months or temperature fluctuations. Remove flower stalks immediately, maintain consistent soil moisture, and choose varieties suited to our day-length. Short-day varieties often bolt in our long summer days.

Pacific Northwest Specific Challenges: Our cool, wet springs can promote fungal issues like pink root, while our dry summers stress plants if not watered consistently. However, our mild heat means fewer pest pressures overall, and cool nights help prevent many stress-related problems common in hotter climates.

Onions make excellent companions for carrots, beets, and lettuce in Pacific Northwest gardens. The strong scent deters carrot flies, while the upright growth doesn't compete with these shorter crops for light during our often overcast growing season. Onions also pair well with tomatoes, helping repel aphids and other soft-bodied insects.

Avoid planting onions near beans and peas, as they can inhibit the nitrogen-fixing bacteria these legumes depend on. This is particularly important in our region where cool soil temperatures already slow bacterial activity in spring, making it harder for legumes to establish their beneficial relationships.