Green Onions in Zone 7A — Northern California

Green onions are a fantastic addition to any Northern California garden. Their mild, fresh flavor elevates countless dishes, and they're incredibly versatile in the kitchen. Plus, the satisfaction of snipping fresh green onions from your garden for a last-minute garnish is hard to beat.

While our Mediterranean climate with its dry summers and occasional water restrictions presents challenges, green onions are surprisingly adaptable. With our long, 235-day growing season, you can enjoy multiple harvests with careful planning and water-wise gardening techniques.

If you're starting green onion seedlings indoors, transplant them outdoors from mid-February through mid-March. Before planting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperature fluctuations.

Space the seedlings 2-3 inches apart in well-drained soil. Keep an eye on the weather forecast – late frosts are always possible in Northern California during this period. If frost is predicted, cover your transplants with row covers or blankets for protection.

Direct sowing is the easiest and most common method for growing green onions in Northern California. Sow seeds from mid-February through late August for a continuous harvest. Choose a spot with full sun to partial shade.

Prepare the soil by loosening it and adding compost or other organic matter. Green onions prefer well-drained soil. Sow seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. For an even easier start, you can also plant the root ends of store-bought green onions directly into the soil!

Green onions need consistent moisture to thrive, especially during our dry Northern California summers. While they aren’t drought-tolerant, careful watering practices can help them flourish even with water restrictions. A good rule of thumb is to aim for about 1 inch of water per week, either from rainfall or irrigation.

During the warmer months, check the soil moisture regularly using the "finger test"—stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in some microclimates. Overhead watering is generally fine in our low-humidity environment, but be mindful of evening watering that doesn't dry before nightfall.

Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to root rot, indicated by mushy or discolored stalks. Applying a layer of mulch, like straw or wood chips, around your green onions helps retain soil moisture and suppress weeds – a win-win in our climate!

You can expect your first harvest of green onions from late April through mid-November, about 60 days after planting. Look for stalks that are at least pencil-thick. Don't wait too long, as overly mature stalks can become tough and strong-flavored.

To harvest, you can either pull the entire plant or cut the stalks off about an inch above the base. If you cut them, the green onions will often regrow, giving you multiple harvests from the same plant. As we approach the first frost in early November, harvest any remaining green onions and store them in the refrigerator. You can also dig up and pot some of your plants to overwinter indoors for fresh greens throughout the winter.

Here are some common problems you might encounter growing green onions in Northern California:

• 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: These pests are attracted to the smell of onions and lay their eggs near the base of the plants.
• How to fix/prevent it: Use row covers to prevent the flies from laying eggs. Introduce beneficial nematodes to the soil. Remove and destroy any infested plants.
• Thrips
• What it looks like: Small, silvery streaks on the leaves, distorted growth, and tiny black specks (thrip droppings).
• What causes it: These tiny insects suck the sap from the leaves, causing damage. They thrive in hot, dry conditions.
• How to fix/prevent it: Spray plants with a strong stream of water to dislodge thrips. Introduce beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil as a last resort.
• 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.
• 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: Roots turn pink or reddish, plants are stunted, and leaves may yellow.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Improve soil drainage. Rotate crops to avoid planting onions in the same spot year after year. Solarize the soil to kill the fungus.

Northern California Specific Challenges: Our moderate-to-hot, dry summers and occasional water restrictions can stress green onions, making them more susceptible to pests and diseases. Consistent watering, mulching, and choosing disease-resistant varieties are key to success in our region.

Companion planting can really boost your green onion crop here in Northern California. Carrots are great companions because their scent deters onion flies. Lettuce benefits from the protection green onions offer against aphids.

Tomatoes and peppers also do well planted near green onions, as the onions can help repel certain pests that target these crops. Beets are another good choice, as they don't compete for the same nutrients and can even help improve soil structure. Avoid planting green onions near beans and peas, as they can inhibit each other's growth.