Green Onions in Zone 8B — 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 versatile in the kitchen. Plus, with our long growing season, you can practically have a year-round harvest right in your backyard.

Sure, we face challenges like drought and the occasional heat wave inland. But green onions are fast-growing and relatively easy to manage, even with water restrictions. Given our 298-day growing season, you'll find that with a little planning, you can enjoy fresh green onions almost any time.

You can transplant green onion seedlings outdoors from mid January through mid February. This gives them a head start before the warmer weather really kicks in. Before planting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

When transplanting, space them about 2-3 inches apart in well-draining soil. Keep an eye on the forecast, as we can still get some unexpected chilly nights this time of year. A little frost cloth can offer protection if needed.

Direct sowing is the way to go with green onions, and luckily, you can do it from mid January through late September here in Southern California. Choose a spot with full sun to partial shade. Prepare the soil by loosening it and adding some compost to improve drainage and fertility.

Sow seeds about ¼ inch deep, spacing them 2-3 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week or two. Pro tip: You can also plant the root ends of store-bought green onions! Just stick them in the soil, and they'll regrow.

Green onions need consistent moisture to thrive, but it's a balancing act, especially with our SoCal climate. During the cooler months, when rainfall is more frequent, you might only need to water once a week, if at all. But come summer, when the heat kicks in inland, you'll likely need to water every other day, or even daily, depending on your soil type.

The finger test is your best friend: 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, adjusting based on rainfall and temperature. 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 or wilting leaves. Overwatering can lead to root rot, indicated by mushy, brown stalks. A layer of mulch around your green onions helps retain moisture and keeps the soil cooler during those hot summer months, which is a lifesaver during fire season.

You can expect your first harvest of green onions starting in mid March, and you can continue harvesting all the way through mid December in Southern California. Green onions are typically ready to harvest about 60 days after planting, when the stalks are about pencil-thick. Don't worry if they aren't perfectly uniform; flavor is the key!

You have two harvest options: You can pull up the entire plant, or you can cut the green onion about an inch above the soil line. If you cut them, they'll often regrow, giving you multiple harvests from the same plant. To encourage continued production, be sure to water and fertilize regularly after harvesting.

As we approach our first frost (usually around early December), harvest any remaining green onions to use fresh or freeze for later. Even if a light frost nips them, they'll often bounce back with the mild winters we have here.

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

• Onion Maggots
• What it looks like: Wilting or yellowing leaves, stunted growth, and small white maggots feeding on 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. Companion planting with carrots can help deter them. Beneficial nematodes can also be used to control maggots in the soil.
• Thrips
• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny, slender insects on the plants.
• What causes it: Thrips are attracted to dry conditions and can be a problem, especially during Santa Ana winds.
• How to fix/prevent it: Provide regular watering and use insecticidal soap or neem oil to control infestations. 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: 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, plants are stunted, and leaves yellow.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Improve soil drainage, rotate crops, and solarize the soil during the hottest months to kill the fungus.

Southern California Specific Challenges: Our hot summers inland can stress green onions, making them more susceptible to pests and diseases. Proper watering is crucial, but be mindful of water restrictions and use water-wise practices like mulching and drip irrigation. The low-to-moderate humidity helps reduce the risk of some fungal diseases, but consistent monitoring is still key.

Companion planting can really boost your green onion crop here in Southern California. Carrots are great companions because they deter onion flies, while the onions repel carrot root flies. Plant lettuce nearby to provide ground cover and help retain moisture in our dry climate.

Tomatoes and peppers also benefit from being planted near green onions, as the onions can help repel certain pests. Beets are another good choice, as they don't compete for the same nutrients in the soil. Avoid planting green onions near beans or peas, as they can inhibit each other's growth.