Green Onions in Zone 10B — Desert Southwest

Green onions are a must-grow in any Desert Southwest garden. Their fresh, mild flavor adds a zing to our southwestern cuisine, and they’re so versatile you'll be adding them to everything from tacos to soups. Plus, the satisfaction of snipping fresh green onions from your own garden, even in January, is hard to beat!

Our extreme heat and alkaline soil can present challenges, but with careful timing and smart gardening practices, you can have green onions thriving almost year-round. We have a 349-day growing season here, so there's plenty of opportunity to get it right.

You can transplant green onion seedlings outdoors from mid-December through mid-January. This gives them a chance to get established before our weather starts to warm up. Before transplanting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space the seedlings 2-3 inches apart in well-draining soil. Keep an eye on the forecast. Even in our mild winters, we can get occasional dips below freezing, so be prepared to cover your transplants if necessary.

Direct sowing is the easiest way to grow green onions in our climate. You can sow seeds from mid-December all the way through mid-October, giving you almost continuous harvests. Prepare your soil by loosening it and amending with compost. Green onions prefer a soil temperature between 60°F and 70°F for optimal germination.

Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seedlings emerge. A fun and easy trick: you can also plant the root ends of store-bought green onions directly into the soil! They'll regrow quickly.

Watering is critical for green onions in our arid climate. They need consistent moisture to produce those tender, mild stalks we love. Their shallow roots mean they can dry out quickly, especially during our hottest months.

During the cooler months (late fall through early spring), water deeply about once a week, providing about 1 inch of water. In the extreme heat of summer, you may need to water every other day, or even daily, to keep the soil consistently moist. 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.

Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, which presents as wilting and mushy stems. A light layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool.

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

You can either pull up the entire plant or cut the green onions off about an inch above the base. If you cut them, they will often regrow, giving you multiple harvests. As our first frost approaches in late December, harvest any remaining green onions to use in your cooking or preserve for later.

Green onions are relatively easy to grow, but they can be susceptible to a few problems in our region:

• 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 thrive in moist soil and can be particularly problematic after our monsoon season.
• How to fix/prevent it: Use row covers to prevent adult flies from laying eggs. Remove and destroy any infested plants. Consider using beneficial nematodes in the soil.
• Thrips
• What it looks like: Silvery or white streaks on the leaves, distorted growth, and tiny black insects visible upon close inspection.
• What causes it: Thrips love our hot, dry conditions. They suck the sap from the leaves, weakening the plant.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings. Spray plants with a strong stream of water or use insecticidal soap.
• 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: This oomycete pathogen spreads in cool, humid conditions via wind-carried spores. While we're arid, our monsoon season can create pockets of humidity.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides can be used for prevention.
• Pink Root
• What it looks like: Roots turn pink or reddish, plants are stunted, and leaves yellow and die.
• What causes it: A soilborne fungus that thrives in warm, wet conditions and alkaline soils.
• How to fix/prevent it: Improve soil drainage and avoid overwatering. Rotate crops to avoid buildup of the fungus in the soil. Solarize the soil during the hottest part of summer to kill the fungus.

Desert Southwest Specific Challenges: The extreme heat and intense sun can stress green onions, making them more susceptible to pests and diseases. Providing afternoon shade with shade cloth, especially during the summer months, is essential. Our alkaline soil can also be a challenge, so amend with plenty of compost to improve drainage and nutrient availability.

Companion planting can help your green onions thrive. Carrots make great companions because they deter onion flies. Lettuce and beets are also good choices, as they have different nutrient needs and won't compete with the green onions. Planting tomatoes and peppers nearby can also be beneficial, as green onions repel some of their common pests.

Avoid planting green onions near beans or peas. These legumes can inhibit the growth of onions. In our Desert Southwest gardens, maximizing space and protecting plants from the harsh sun is key, so choose companions that offer mutual benefits and don't create unnecessary competition.