Green Onions in Zone 9A — Southern California

Green onions are a must-grow in Southern California. Their mild, fresh flavor elevates everything from tacos to salads, and they’re incredibly easy to grow in our mild winters and long, warm season. Plus, there's nothing quite like snipping fresh green onions from your garden for dinner—a real taste of homegrown satisfaction.

Our SoCal climate does have its quirks, like the occasional heat spike and the need to conserve water. But don't worry, with a little planning and awareness of our 322-day growing season, you can enjoy a year-round harvest of these versatile veggies.

You can transplant green onion seedlings outdoors from early January through early February. This gives them a head start before the weather really warms up.

Before planting, remember to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind, preventing transplant shock. Space them about 2-3 inches apart in well-drained soil.

Keep an eye on the forecast during this time. Even though we rarely get a hard freeze, a sudden cold snap can still stress young plants. Cover them with horticultural fleece if temperatures dip unexpectedly.

Direct sowing green onions is the easiest way to grow them here in Southern California, and you can do it from early January through early October. This long planting window takes advantage of our mild climate.

Choose a spot with full sun to partial shade. Prepare the soil by loosening it and mixing in some compost. Green onions aren't too picky, but they appreciate well-draining soil. Sow seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until they germinate.

Here's a little SoCal gardening hack: You can also plant the root ends of store-bought green onions! Just stick them in the ground, and they'll usually regrow. It's a quick and easy way to get a continuous supply.

Green onions need consistent moisture to thrive, but they definitely don't like soggy soil. In our Southern California climate, that means adjusting your watering schedule with the seasons.

During the cooler, wetter months (late fall through early spring), you may only need to water once a week, or even less if we get decent rainfall. Use the "finger test": stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. As the weather warms up in late spring and summer, you'll need to water more frequently, possibly every other day, especially inland where the summer heat can be intense.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our low-to-moderate humidity. Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, indicated by wilting and mushy stalks. Adding a layer of mulch around your green onions helps retain moisture in the soil and keep the roots cool, which is especially helpful during those hot summer months.

You can expect your first harvest of green onions about 60 days after planting, typically from early March through late December in our Southern California climate.

Look for stalks that are about pencil-thick. To harvest, you can either pull up the entire plant or cut the stalks about an inch above the base. If you cut them, they'll usually regrow, giving you multiple harvests.

For continuous production, stagger your plantings every few weeks. As our first frost approaches around mid- December, harvest any remaining green onions to use fresh or preserve. You can also cover them with a thick layer of mulch to protect them from light frost and extend the harvest a bit longer.

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

• Onion Maggots
• What it looks like: Wilting or yellowing plants, stunted growth, and small white maggots feeding on the roots and bulb.
• What causes it: These pests are attracted to the onion smell 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 infested plants.
• Thrips
• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny, slender insects visible on the plant.
• What causes it: These tiny insects suck the sap from the leaves, causing damage. They thrive in hot, dry conditions, which we often get during Santa Ana winds.
• How to fix/prevent it: Spray plants with a strong stream of water to dislodge thrips. Insecticidal soap or neem oil can also be effective. 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: An 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.
• Pink Root
• What it looks like: Roots turn pink or reddish, and the plant growth is stunted.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Ensure good soil drainage. Rotate crops to avoid buildup of the fungus in the soil. Solarize the soil during the hot summer months to kill the fungus.

Southern California Specific Challenges: Our hot, dry summers can stress green onions, making them more susceptible to pests. While our winter-wet rainfall can sometimes create conditions favorable for fungal diseases like downy mildew. Consistent monitoring and proactive measures are key to keeping your green onions healthy.

Green onions are great companions for many plants in your Southern California garden. Carrots benefit from green onions because the onion scent repels carrot root flies. Lettuce appreciates the shade provided by green onions, especially during our hotter months.

Tomatoes and peppers also do well with green onions as they can help deter pests like aphids. Beets are another good companion because green onions can help protect them from flea beetles. Avoid planting green onions near beans and peas, as they can inhibit their growth.