Onion in Zone 8A — Pacific Northwest

Onions are one of the most satisfying crops for Pacific Northwest gardeners, offering exceptional flavor that far surpasses anything you'll find in stores. Our mild summers and cool nights create ideal conditions for developing complex, sweet onions that store beautifully through our long, wet winters. The versatility is unmatched — from fresh green onions in early summer to cured storage onions that last until next year's harvest.

While our wet springs can slow early growth and cool soil temperatures challenge warm-season crops, onions actually thrive in our climate conditions. With our generous 203-day growing season and rarely scorching temperatures, you have plenty of time to grow substantial bulbs whether you start from seeds, sets, or transplants. The key is working with our spring timing rather than against it.

Starting onion seeds indoors makes sense if you want the largest possible bulbs or specific varieties not available as sets. Begin sowing in early to late January, about 10 weeks before your planned transplant date in late March through mid-April. Our slow Pacific Northwest springs actually work in your favor here — you won't be rushing to get seedlings outdoors.

Set up seed trays with good potting mix in a warm spot (65-70°F) with bright light once seeds germinate. Bottom watering works best for onion seedlings since they're prone to damping off with overhead moisture. The seedlings will look like thin grass blades and grow slowly — this is normal.

Keep in mind that onion sets are much easier for beginners and still produce excellent results in our climate. Seeds are worth the extra effort only if you want specific varieties or the satisfaction of growing from scratch.

Transplant your onion seedlings outdoors from late March through mid-April, when soil temperatures consistently stay above 40°F. Our Pacific Northwest springs can be unpredictable with cool, overcast days followed by warm spells, so hardening off is crucial. Gradually expose seedlings to outdoor conditions over a week.

Space transplants 4-6 inches apart in rows, planting them slightly deeper than they were in their containers. The cool, wet conditions typical of our spring weather actually help transplants establish without shock. Just ensure your planting beds drain well since soggy soil can rot young onions.

For the easiest approach, consider onion sets instead of transplants. These small bulbs are practically foolproof in our climate and available at every garden center by mid-March.

Direct sowing onion seeds works well in the Pacific Northwest from mid-March through early July, though earlier plantings typically produce larger bulbs. Wait until soil temperatures reach at least 45°F — our cool spring soils often delay this until late March. The soil should be workable and not muddy from our typical wet spring weather.

Prepare your beds with compost and ensure good drainage, as onions won't tolerate waterlogged conditions. Sow seeds ¼ inch deep and space them 4-6 inches apart, or sow more densely and thin later. Our mild summers mean you can even make succession plantings into early summer for continuous green onion harvests.

Direct sowing onion sets (small bulbs) is often more reliable than seeds in our climate. Plant sets pointed end up, just barely covered with soil, spacing them 4-6 inches apart.

Onions need consistent moisture throughout their growing season, but our Pacific Northwest climate makes this manageable without excessive irrigation. During our typically wet spring months, natural rainfall usually provides adequate water. Begin monitoring soil moisture more closely once our dry summer months arrive in July.

Check soil moisture by sticking your finger 2 inches deep — if it's dry, it's time to water. Onions generally need about 1 inch of water per week during active growth. Water at the base of plants rather than overhead to prevent disease issues, especially important during our humid spring conditions. Our mild summer temperatures (rarely above 90°F) mean you won't need the intensive watering schedules required in hotter climates.

Stop watering completely when onion tops begin to fall over and yellow in late summer — this signals the start of the curing process. Continued watering at this stage can actually harm storage quality and increase rot potential.

A 2-3 inch layer of mulch helps retain moisture during our dry summer months while suppressing weeds. Straw or shredded leaves work well and won't compete with the shallow onion roots for nutrients.

Your first onions will be ready for harvest anywhere from late June through early November, depending on when you planted and which varieties you chose. The telltale sign is when the green tops begin falling over and turning yellow — this happens naturally as the bulbs mature and energy moves from the leaves into storage.

Pull onions on a dry day if possible, gently lifting them from the soil with their tops intact. Brush off excess dirt but don't wash them — wet onions are prone to rot. In our Pacific Northwest climate, you'll often get a stretch of dry weather in late summer that's perfect for curing.

Cure freshly harvested onions in a warm, dry, well-ventilated area for 2-3 weeks before storing. Our garages or covered porches work well during the typically dry late summer period. Properly cured onions will have papery outer skins and dried tops.

As our first frost approaches in late October, make sure to harvest any remaining onions even if they haven't fully matured. Smaller onions should be used fresh rather than stored, but they're still perfectly good for cooking.

Onion Thrips These tiny insects create silvery streaks and stippling on onion leaves, eventually causing tips to brown and die back. You might see the small, yellowish insects themselves on closer inspection. Thrips thrive in our warm, dry summer conditions and can weaken plants significantly.

Heavy infestations often occur during hot spells in July and August. Row covers during the most vulnerable growth period help prevent initial infestations. Beneficial insects like ladybugs and lacewings provide natural control, and insecticidal soap sprays can reduce severe populations.

Pink Root This soil-borne fungal disease causes onion roots to turn pink, then purple, and eventually die. Affected plants show stunted growth and yellowing leaves, particularly noticeable during our spring growing period. The roots become brittle and unable to take up nutrients effectively.

Pink root thrives in our cool, wet spring soils and can persist for years. Improve drainage and avoid planting onions in the same location for at least three years. Choose resistant varieties when available and ensure good air circulation between plants.

Bolting Onions send up premature flower stalks, shifting energy from bulb development to seed production. You'll see tall, round flower heads emerging from the center of the plant. Once bolted, the bulb stops growing and becomes woody.

Cool spring temperatures followed by warm weather can trigger bolting, common in our variable Pacific Northwest spring climate. Plant at the appropriate time for your variety — long-day onions are best for our region. Remove flower stalks immediately if they appear, though the bulbs may not store as well.

Pacific Northwest Specific Challenges: Our region's combination of wet springs and dry summers actually favors onion growing, but watch for slug damage during wet periods and ensure adequate drainage to prevent root rot diseases that thrive in our clay soils.

Onions make excellent companions for many crops in Pacific Northwest gardens. Plant them alongside carrots — the onions deter carrot flies while carrots help break up soil for onion root development. Beets also pair well, as both crops have similar water needs and the beet greens provide quick shade during our variable spring weather. Lettuce benefits from onion's pest-deterrent properties while making efficient use of space between slower-growing onion bulbs.

Avoid planting onions near beans or peas, as these legumes can actually inhibit onion growth through root competition and different soil pH preferences. The nitrogen-fixing activity of legumes can also encourage excessive leaf growth in onions at the expense of bulb development, particularly problematic in our nutrient-rich Pacific Northwest soils.