Green Onions in Zone 8B — Northern California

Green onions are a staple in any NorCal kitchen, and they're incredibly easy to grow in our Mediterranean climate. Their mild, fresh flavor elevates everything from tacos to salads, and there's nothing quite like snipping a few straight from your garden for dinner. Plus, they're perennials, so you can enjoy them year after year.

Even with our long growing season of 269 days and mild winters, we still face challenges like drought and occasional temperature swings. But don't worry, with a little planning, you can have a continuous supply of green onions from spring through fall. The key is understanding our local microclimates and adjusting your planting schedule accordingly.

If you're starting your green onions indoors or purchasing transplants, aim to get them in the ground from early February through early March. This gives them a head start before the warmer weather arrives.

Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperature fluctuations we often see in early spring. Space the transplants 2-3 inches apart to give them room to grow.

Keep an eye on the forecast for any late frosts, which can still happen in early spring. If a frost is predicted, cover your young plants with row covers or blankets to protect them.

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

Choose a spot with full sun to partial shade and prepare the soil by loosening it and adding compost. Green onions prefer well-drained soil. Sow the 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. For a continuous harvest, sow a new batch of seeds every few weeks. You can also plant the root ends of store-bought green onions – just stick them in the soil and watch them regrow!

Green onions need consistent moisture to thrive, especially during our dry summers. While they aren't drought-tolerant, you can manage watering effectively in our Mediterranean climate.

During the cooler spring and fall months, water deeply about once a week, providing around 1 inch of water. In the hotter summer months, increase watering to 2-3 times a week, providing 1-2 inches of water each time. Always check the soil moisture before watering. 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 our occasionally humid microclimates. Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to root rot, so watch for soggy soil and stunted growth. Mulching around your green onions with straw or wood chips will help retain moisture and suppress weeds, a huge help during our dry summers.

You can expect your first harvest of green onions about 60 days after planting, typically from early April through early December in our region. They're ready to harvest when the stalks are about pencil-thick.

You can either pull up the entire plant or cut the green onion about an inch above the base, leaving the roots in the ground. If you cut them, they will regrow, providing you with multiple harvests. For a continuous supply, harvest a few green onions at a time, rather than harvesting all of them at once.

As the first frost approaches in late November, you can protect your green onions with row covers or mulch to extend the harvest. Even if the tops die back, the roots will often survive the winter and resprout in the spring, giving you an early start to the next season.

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

• Onion Maggots
• What it looks like: Wilting plants, yellowing leaves, and small white maggots in the soil near the roots.
• What causes it: These pests thrive in moist soil and can be attracted to the smell of onions.
• How to fix/prevent it: Use row covers to prevent adult flies from laying eggs near your plants. Rotate your crops each year, and remove any infested plants immediately.
• Thrips
• What it looks like: Silvery streaks on the leaves, distorted growth, and tiny, slender insects on the plants.
• What causes it: Thrips are attracted to dry, stressed plants.
• How to fix/prevent it: Keep your plants well-watered, especially during our dry summers. Introduce beneficial insects like ladybugs and lacewings to your garden. 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, 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: Pink or reddish roots, stunted growth, and yellowing leaves.
• What causes it: A soilborne fungus that thrives in warm, wet conditions.
• How to fix/prevent it: Improve soil drainage by adding compost and avoiding overwatering. Rotate your crops each year, and plant resistant varieties if available.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress green onions, making them more susceptible to pests and diseases. Consistent watering and proper soil preparation are key to keeping your plants healthy. Also, be mindful of water restrictions during drought periods and adjust your watering accordingly.

Green onions are great companions for many plants in your Northern California garden. They deter pests and improve the flavor of nearby crops.

• Good companions:
• Carrots: Green onions repel carrot root flies, protecting your carrot crop.
• Lettuce: Green onions help deter aphids and other pests that can damage lettuce.
• Tomatoes and Peppers: Green onions can repel aphids and other pests that commonly attack tomatoes and peppers, leading to healthier, more productive plants.
• Beets: Green onions can help deter leaf miners, which can damage beet leaves.
• Bad companions:
• Beans and Peas: Green onions can inhibit the growth of beans and peas, so it's best to keep them separated.