Green Onions in Zone 9B — Southern California

Green onions are a must-have in any Southern California garden. They're incredibly versatile in the kitchen, adding a mild oniony flavor to everything from tacos to salads, and they're so easy to grow here with our long, warm season. Plus, there's nothing quite like the satisfaction of snipping fresh green onions from your own backyard, especially when you can do it practically year-round.

We do face challenges like drought and the occasional heat wave inland, but with a little planning, you can enjoy a continuous harvest of green onions. Our 334-day growing season gives you plenty of opportunity to get it right, and the timing for planting and growing them helps avoid the worst of the summer heat.

If you prefer to start your green onions indoors, you can transplant them outdoors from late December through late January. This helps them get established before our warmer weather kicks in. Be sure to harden them off for about a week before transplanting, gradually exposing them to the outdoor elements.

When transplanting, space the seedlings about 2-3 inches apart in well-draining soil. Keep an eye on the weather forecasts around this time; we can sometimes get unexpected cold snaps, so be prepared to cover your seedlings if necessary.

Direct sowing is the easiest and most common method for growing green onions in Southern California. You can sow seeds directly into your garden from late December through mid October, giving you nearly year-round planting opportunities. Soil temperatures between 60-70°F are ideal for germination, which is generally easily achieved in our climate.

Prepare your soil by loosening it and adding some compost or other organic matter. Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seedlings emerge. For a continuous harvest, sow a new batch of seeds every few weeks. Another easy trick: plant the root ends of store-bought green onions directly into the soil!

Green onions need consistent moisture to thrive, but overwatering can lead to problems. In Southern California's climate, especially during our hot summers inland, watering is crucial. Aim to keep the soil consistently moist, but not soggy.

During the cooler months, our winter rains usually provide enough moisture, but you'll still want to check the soil. From spring through fall, especially during hotter periods, you'll need to water more frequently. A good rule of thumb is to water deeply about 1 inch per week, but always check the soil moisture first. Stick your finger about 2 inches deep; 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, especially with our low-to-moderate humidity. Signs of underwatering include wilting or yellowing leaves, while overwatering can lead to yellowing leaves and potentially root rot. Mulching around your green onions with straw or wood chips can help retain moisture in the soil and keep the roots cool, particularly important during our summer heat.

You can expect your first harvest of green onions from late February through early January, about 60 days after planting. They're ready to harvest when the stalks are about pencil-thick. A good sign is when they're about 6-8 inches tall.

You can either pull the entire plant or cut the green onion about an inch above the soil line. If you cut them, they'll often regrow, giving you multiple harvests. To encourage continued production, be sure to keep the soil moist and fertilize lightly after each harvest. As we approach our first frost in late December, you can harvest the remaining green onions or cover them to protect them from the cold, potentially extending your harvest a bit longer.

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

• Onion Maggots
• What it looks like: Wilting plants, yellowing leaves, 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 the adult flies from laying eggs. Rotate your crops each year. Introduce beneficial nematodes to the soil.
• Thrips
• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny, slender insects visible upon close inspection.
• What causes it: Thrips are attracted to dry conditions and can be more prevalent during our 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: 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's growth is stunted.
• What causes it: A soilborne fungus that is more prevalent in warm, moist conditions.
• How to fix/prevent it: Improve soil drainage. Rotate crops to avoid planting onions in the same spot year after year. Plant resistant varieties.

Southern California Specific Challenges: The combination of our hot, dry summers and occasional winter rains can create ideal conditions for both pests and diseases. The extreme heat inland can also stress plants, making them more susceptible to problems. Be vigilant about monitoring your plants and take action quickly to address any issues. Water deeply and infrequently to encourage strong root growth, and be sure to provide adequate spacing for good air circulation.

Companion planting can really help your green onions thrive here in Southern California. Carrots are great companions because they deter onion flies, and green onions, in turn, deter carrot root flies. Lettuce also benefits from being planted near green onions, as the onions can help repel aphids. Tomatoes and peppers enjoy the protection from various pests that green onions provide. Beets are another good choice, as they don't compete for the same nutrients and can even improve soil health. Avoid planting green onions near beans or peas, as they can inhibit each other's growth.