Green Onions in Zone 8B — Pacific Northwest

Green onions are a must-grow in the Pacific Northwest. Their mild, fresh flavor elevates everything from stir-fries to salads, and they’re so easy to grow here with our mild summers and cool nights that bring out the best in their taste. Plus, the satisfaction of snipping fresh green onions from your garden, rather than buying them at the store, is hard to beat.

We do have our gardening quirks here. The cool soil in spring can slow things down and late blight is always a concern. But with a 210-day growing season, there's plenty of time to get a continuous harvest of green onions from early spring well into fall.

You can transplant green onion starts outdoors from early March through early April. Give your seedlings about a week to harden off before planting. Gradually expose them to outdoor conditions, starting with a few hours of sheltered sunlight each day.

When you're ready to plant, space them 2-3 inches apart in well-draining soil. Keep an eye on the weather forecast, as we can still get some chilly temperatures and overcast spring days during this time. If a hard frost threatens, be prepared to cover your transplants.

Direct sowing is the preferred method for green onions, and it's super easy. You can sow seeds directly into the garden from early March through mid August. Choose a spot with full sun to partial shade.

Prepare the soil by loosening it and removing any rocks or debris. Green onions aren't too fussy, but they appreciate well-draining soil. Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seeds germinate, which usually takes about a week or two. You can also plant the root ends of store-bought green onions; just stick them in the ground and keep them watered.

Green onions need consistent moisture to thrive, especially during our dry summer months. They aren't drought-tolerant and their shallow roots can dry out quickly. The goal is to keep the soil consistently moist, but not waterlogged.

During our wet springs, you might not need to water much at all. But once those dry summer months hit, check the soil regularly. Stick your finger about 2 inches deep; if it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the foliage, which can help prevent fungal diseases in our humid, dry-summer climate.

Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to root rot, so watch out for stunted growth and soggy soil. A light layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool during the summer.

You can expect your first harvest of green onions around early May if you planted early, and continue harvesting well into early November. They're typically ready to harvest about 60 days after planting, when the stalks are about pencil-thick.

To harvest, you can either pull the entire plant or cut the stalks off above the base, about an inch or two above the soil line. If you cut them, they'll usually regrow, giving you multiple harvests from a single planting. For continuous production, sow new seeds every few weeks throughout the growing season.

As the first frost approaches in early November, harvest any remaining green onions. You can store them in the refrigerator for a week or so, or chop and freeze them for later use.

Here are some common problems you might encounter with green onions in the Pacific Northwest:

Onion Maggots

• What it looks like: Wilting or yellowing leaves, stunted growth, and small white maggots feeding on the roots and bulb.
• What causes it: Onion maggots are the larvae of a fly that lays its eggs near the base of onion plants. They thrive in cool, moist soil, which we often have in spring.
• How to fix/prevent it: Use row covers to prevent the flies from laying eggs. Apply beneficial nematodes to the soil to control the larvae. Rotate crops each year.

Thrips

• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny, slender insects on the plants.
• What causes it: Thrips are tiny insects that feed on plant sap. They are more common during dry weather, but can still be a problem in our mild summers.
• How to fix/prevent it: Spray plants with insecticidal soap or neem oil. Encourage beneficial insects like ladybugs and lacewings.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides. Leaves brown and die from the bottom up.
• What causes it: Oomycete pathogen that spreads in cool, humid conditions via wind-carried spores. Different species affect different plants. We have cool, wet springs, which encourages downy mildew.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides for prevention. Plant resistant varieties where available.

Pink Root

• What it looks like: Pink or reddish roots, stunted growth, and yellowing leaves.
• What causes it: A soilborne fungus that infects the roots. It's more common in warm, wet soils.
• How to fix/prevent it: Improve soil drainage. Rotate crops. Plant resistant varieties. Solarize the soil to kill the fungus.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall can actually be beneficial for green onions, as they prefer cooler temperatures and don't like overly wet conditions. However, late blight, which affects tomatoes and potatoes, can sometimes spread to onions. Be vigilant about monitoring your plants and taking preventative measures.

Green onions are great companions for many plants in the Pacific Northwest garden. Carrots benefit from green onions because the onion's scent deters carrot root flies. Lettuce thrives near green onions as they offer shade and protection from pests. Tomatoes and peppers enjoy the pest-repelling properties of green onions. Beets also appreciate being near green onions, which can help deter flea beetles.

Avoid planting green onions near beans and peas, as they can inhibit their growth. The alliums in green onions may stunt the growth of legumes, so keep them separated in your garden beds.