Green Onions in Zone 10A — Southern California

Green onions are a SoCal gardener's best friend. They're incredibly versatile in the kitchen, adding a fresh, mild onion flavor to everything from tacos to salads, and they're ridiculously easy to grow in our mild climate. Plus, there's nothing quite like the satisfaction of snipping a few green onions from your own garden for dinner, even in the middle of "winter".

Sure, we have our challenges here – drought, the occasional heat wave, and those pesky Santa Ana winds. But with our long growing season, you can pretty much have green onions going year-round if you plan it right. Our 349-day growing season gives you plenty of wiggle room to dial in your planting schedule.

If you want to get a head start, you can transplant green onions outdoors from mid-December through mid-January. This is a smaller window than direct sowing, but it works if you've started seeds indoors or purchased seedlings.

Before planting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Plant them 2-3 inches apart in well-draining soil.

Keep an eye on the weather forecast; even though we rarely get hard freezes, a sudden cold snap can stress young transplants. Protect them with row covers if needed.

Direct sowing is the easiest way to grow green onions in Southern California. You can sow seeds directly into the garden from mid-December all the way through mid-October. That's a HUGE window!

Prepare your soil by loosening it and amending with compost. Green onions prefer soil temperatures between 60°F and 70°F for optimal germination. Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until they sprout. A fun tip? You can even plant the root ends of store-bought green onions for a quick and easy start!

Green onions need consistent moisture to thrive, especially in our semi-arid climate. While they aren't drought-tolerant, you can manage their water needs effectively with a smart watering schedule.

During the cooler months (late fall through early spring), when we get some rainfall, you might only need to supplement with watering once or twice a week, giving them about 1 inch of water. In the hotter summer months, especially inland, you'll likely need to water every other day, or even daily, providing about 1-2 inches of water per week. Always check the soil moisture about 2 inches deep – the "finger test" – before watering. 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 moderate humidity. Signs of underwatering include wilting and yellowing leaves, while overwatering can lead to root rot. A light layer of mulch, like straw or wood chips, can help retain moisture and regulate soil temperature, which is especially helpful during those hot summer months.

In Southern California, you can expect your first green onion harvest from mid-February through early January, about 60 days after planting. Look for stalks that are pencil-thick or slightly larger.

You can either pull the entire plant or, for a continuous harvest, snip the green stalks about an inch above the soil line. The plant will then regrow, giving you multiple harvests.

As late December approaches and our first frost is on the horizon, harvest any remaining green onions you want to use. While they are frost-hardy, a hard freeze can damage the leaves. You can also dig them up and pot them to keep them growing indoors over the winter.

Green onions are generally easy to grow, but here are a few common problems to watch out for in Southern 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 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. Rotate crops to avoid build-up in the soil. Introduce beneficial nematodes to the soil.
• Thrips
• What it looks like: Silver streaks or white patches on the leaves, distorted growth, and tiny, slender insects (thrips) visible on the plant.
• What causes it: Thrips are attracted to dry, hot conditions and can be blown in by the Santa Ana winds.
• How to fix/prevent it: Keep plants well-watered. Spray plants with a strong stream of water to dislodge thrips. Use insecticidal soap or neem oil.
• 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.
• 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, and the plant becomes stunted and weak.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Improve soil drainage. Rotate crops. Solarize the soil during the hot summer months. Plant resistant varieties if available.

Southern California Specific Challenges: Our hot summers inland can stress green onions, making them more susceptible to pests and diseases. The low-to-moderate humidity can help prevent some fungal issues, but it also means you need to be diligent about watering. During fire season, be extra cautious about watering to keep plants hydrated, but avoid creating overly moist conditions that could attract pests.

Companion planting can really boost your green onion game. Carrots are great companions because their scent can repel onion flies, while green onions can deter carrot root flies. Lettuce thrives in the partial shade provided by green onions, and the onions can help repel aphids from tomatoes and peppers. Beets also benefit from being planted near green onions, as the onions can deter flea beetles.

Avoid planting green onions near beans and peas. These legumes can inhibit the growth of onions, and the onions can also hinder the nitrogen-fixing abilities of the legumes.