Green Onions in Zone 10B — Southern California

Green onions are a SoCal gardener's dream – they're incredibly versatile in the kitchen, adding a fresh bite to everything from tacos to salads, and they're ridiculously easy to grow here. Plus, nothing beats the satisfaction of snipping a few green onions from your own garden for dinner, especially when they taste so much better than anything you'll find at the store.

We definitely have our challenges here in Southern California, from water restrictions to the occasional heat wave, but green onions are pretty forgiving. With a little attention to watering and some smart planting, you can enjoy a nearly year-round harvest in our 355-day growing season.

If you want to get a head start, you can transplant green onions outdoors from mid-December through early January. Before you put them in the ground, make sure you harden them off. Give them about a week of gradual exposure to the outdoors, increasing their time outside each day.

Space your transplants about 2-3 inches apart. Keep an eye on the weather forecast – even though we rarely get a hard freeze, a sudden cold snap can still stress young transplants.

Direct sowing is the easiest way to grow green onions, and you can do it from mid-December all the way through mid-October here in Southern California. Choose a spot with full sun to partial shade. Before sowing, amend the soil with compost to improve drainage and fertility.

Sow seeds about a quarter-inch deep, spacing them 2-3 inches apart. Keep the soil consistently moist until they germinate. A fun trick is to 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, especially in our Southern California climate. While we don't get a ton of rain, it's important to pay attention to watering, especially during the hotter months. Aim to keep the soil consistently moist, but not waterlogged, for the best flavor and texture.

During the cooler months, you might only need to water once or twice a week, depending on rainfall. In the summer heat inland, though, you'll likely need to water every other day, or even daily during heat waves. 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 the weather. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our moderate humidity.

If the leaves start to yellow and droop, you're likely overwatering. If they get dry and crispy at the tips, you're underwatering. A layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool, which is especially helpful during our hot summers.

You can expect your first harvest of green onions from mid-February through early January, about 60 days after planting. The best time to harvest is when the stalks are about pencil-thick. Don't wait too long, or they can get tough.

You can either pull up the entire plant or cut the green onions off about an inch above the soil line. If you cut them, they'll often regrow for another harvest. Keep harvesting regularly to encourage continued production. As we approach late December and the chance of frost increases, harvest any remaining green onions to use or preserve.

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 in the soil near the roots.
• What causes it: These pests thrive in moist soil and attack the roots of onion family plants.
• How to fix/prevent it: Rotate your crops, use row covers to prevent adult flies from laying eggs, and introduce beneficial nematodes to the soil.

Thrips

• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny black specks (thrip droppings).
• What causes it: These tiny insects suck the sap from leaves, especially during hot, dry weather.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings, use insecticidal soap or neem oil, and water regularly to reduce plant stress.

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 red, and the plant's growth is stunted.
• 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 summer to kill the fungus.

Southern California Specific Challenges: Our hot summers inland can stress green onions, making them more susceptible to pests and diseases. Consistent watering and some afternoon shade can help. Also, our winter-wet rainfall can create conditions favorable for fungal diseases, so good air circulation and careful watering practices are essential.

Companion planting can really boost your green onion crop here in Southern California. Carrots are great companions because their scent deters onion flies. Lettuce also works well, as it provides ground cover that helps retain moisture in our dry climate. Tomatoes and peppers benefit from green onions because they repel pests like aphids. Beets are also good companions, as they don't compete for the same nutrients.

Avoid planting green onions near beans and peas. These legumes can inhibit the growth of onions. Knowing these pairings can help you maximize your garden's potential.