Green Onions in Zone 8A — Desert Southwest

Green onions are a must-grow for any Desert Southwest gardener. Their fresh, mild flavor elevates everything from tacos to salads, and there's nothing quite like snipping a few from your own backyard. Plus, they're incredibly versatile—you can use the whole plant, from the white bulb to the green tops.

Sure, our extreme heat and arid conditions can be tough, but with smart timing, you can easily enjoy a continuous harvest of green onions throughout our long, 265-day growing season. You'll find that planting at the right time lets you avoid the worst of the summer heat.

You can transplant green onion seedlings outdoors from early February through early March. This gives them a good head start before the extreme heat hits. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

When you're ready to plant, space them about 2-3 inches apart in well-draining soil. Keep an eye on the weather—those early weeks can still bring unexpected temperature swings. Protect young transplants with shade cloth if necessary, especially during the hottest part of the day.

Direct sowing is the easiest way to grow green onions in the Desert Southwest, and you can do it from early February through mid September. Choose a spot with full sun to partial shade, especially during the hottest months. Prepare the soil by loosening it and adding compost.

Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seedlings emerge. You can also plant the root ends of store-bought green onions—just stick them in the ground, and they'll regrow!

Green onions need consistent moisture to thrive in our arid climate. They aren't drought-tolerant, and their shallow roots dry out quickly. During the cooler spring and fall months, aim for about 1 inch of water per week.

In the extreme heat of summer, increase that to 2 inches per week. Use the finger test: stick your finger about 2 inches into the soil. 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 during our monsoon season.

Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, so make sure your soil drains well. A layer of mulch around your plants helps retain moisture and keep the soil cool.

You can expect your first harvest of green onions from early April through early December, about 60 days after planting. Look for stalks that are at least pencil-thick. You can either pull the entire plant or cut the green tops about an inch above the soil.

If you cut them, they'll regrow, giving you a continuous harvest. To encourage further growth, side-dress with compost after harvesting. As the first frost approaches in late November, harvest any remaining green onions to use fresh or freeze for later.

Here are some common problems you might encounter growing green onions in the Desert Southwest:

Onion Maggots

• What it looks like: Wilting or yellowing plants, stunted growth, and small white maggots feeding on the roots and bulbs.
• What causes it: These pests thrive in moist soil.
• How to fix/prevent it: Rotate crops. Use row covers to prevent adult flies from laying eggs. Introduce beneficial nematodes to the soil.

Thrips

• What it looks like: Silvery streaks or stippling on leaves, distorted growth, and tiny, slender insects on the plants.
• What causes it: Thrips are attracted to stressed plants, and our arid conditions can exacerbate the problem.
• How to fix/prevent it: Provide adequate water. Spray plants with a strong stream of water or insecticidal soap. 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 bulbs are small.
• What causes it: A soilborne fungus that thrives in warm, moist conditions. Alkaline soil can make it worse.
• How to fix/prevent it: Improve soil drainage. Rotate crops. Solarize the soil during the hottest part of summer to kill the fungus.

Desert Southwest Specific Challenges: The extreme heat and low humidity can stress green onions, making them more susceptible to pests and diseases. During the monsoon season, watch out for fungal issues and ensure good air circulation. Alkaline soil can also be a problem, so amend your soil with plenty of compost.

Good companions for green onions include carrots, lettuce, tomatoes, peppers, and beets. Carrots deter onion flies, while onions deter carrot flies. Lettuce provides ground cover, keeping the soil cool and moist. Tomatoes and peppers benefit from the onion's pest-repelling properties. Beets help loosen the soil, improving drainage.

Avoid planting green onions near beans and peas. Onions can inhibit their growth.