Green Onions in Zone 8A — Northern California

Green onions are a must-grow in any Northern California garden. Their mild, fresh flavor adds zing to everything from tacos to salads, and the sheer versatility is unmatched. Plus, the satisfaction of snipping fresh green onions from your own garden, even in our mild winters, is hard to beat!

Sure, we have our challenges in NorCal, from occasional drought to the ever-present threat of fire season. But with our long, 255-day growing season and generally mild climate, you'll find green onions are pretty easy to grow with the right timing.

You can transplant green onion seedlings outdoors in early February through early March here in Northern California. This gives them a head start before our summers ramp up. Be sure to harden off your seedlings for about a week by gradually exposing them to outdoor conditions before planting.

When transplanting, space the seedlings about 2-3 inches apart. Keep an eye on the weather forecast – a late cold snap can happen, so be prepared to cover them if temperatures dip unexpectedly.

Direct sowing is the easiest and most common way to grow green onions here. You can sow seeds directly into the garden from early February through early September. This long window takes advantage of our extended growing season.

To prepare the soil, choose a spot with full sun to partial shade and loosen the soil. Green onions prefer soil temperatures around 60-70°F for optimal germination. Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist. For a super easy start, try planting the root ends of store-bought green onions – they'll often regrow!

Watering is key to growing tender, mild green onions in Northern California. While we have a Mediterranean climate with dry summers, green onions aren't drought-tolerant and need consistent moisture. Their shallow roots dry out quickly, especially when the summer heat kicks in.

During the cooler spring and fall, water deeply about once a week, providing around 1 inch of water. As temperatures rise in the summer, increase watering to 2-3 times per week, ensuring they receive about 1-2 inches of water each time. Always check the soil moisture before watering – stick your finger about 2 inches deep; if it feels dry, it's time to water. Watering at the base of the plants is best to avoid wetting the foliage, which can help prevent disease in our low-humidity environment.

Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, indicated by wilting, even with moist soil. Adding a layer of mulch, like straw or wood chips, around your green onions helps retain moisture and regulate soil temperature, which is especially important during our hot, dry summers.

You can expect your first harvest of green onions from mid April through late November, about 60 days after planting. Look for stalks that are at least pencil-thick, usually around 60-70 days after planting. That's when they're at their peak flavor.

To harvest, you can either pull up the entire plant or cut the green onion above the base, leaving the roots in the ground. If you cut them, they'll often regrow, giving you a continuous harvest. To encourage continued production, snip off any flower stalks that appear. As our first frost approaches in mid- November, harvest any remaining green onions or cover them with a frost blanket to extend the harvest a bit longer.

Here are some common problems you might encounter with 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 adult flies from laying eggs. Apply beneficial nematodes to the soil to kill the maggots. Rotate your crops each year to avoid build-up in the soil.

Thrips

• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny, slender insects visible on the plants.
• What causes it: These tiny pests suck the sap from the leaves, causing damage. They thrive in hot, dry conditions.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings. Spray plants with a strong stream of water to dislodge thrips. Insecticidal soap can also be effective.

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 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.

Pink Root

• What it looks like: Roots turn pink or reddish, and plants become stunted and weak.
• What causes it: A soilborne fungus that thrives in warm, moist soil.
• How to fix/prevent it: Improve soil drainage. Rotate crops to avoid build-up of the fungus in the soil. Plant resistant varieties where available.

Northern California Specific Challenges: Our moderate-to-hot summers, combined with low humidity and dry-summer rainfall, can stress green onions. The dry conditions can make them more susceptible to thrips, while inconsistent watering can weaken them, making them vulnerable to other pests and diseases. Consistent watering and good soil management are key to keeping your green onions healthy in our climate.

Green onions are great companions for many plants in your Northern California garden. Plant them near carrots, as the onion's scent can deter carrot flies. Lettuce also benefits from being planted near green onions, as they can help repel aphids. Tomatoes and peppers thrive alongside green onions, as they can deter pests like spider mites. Beets also make good companions, as green onions can help repel flea beetles.

Avoid planting green onions near beans and peas, as they can inhibit the growth of these legumes.