Green Onions in Zone 9B — Desert Southwest

Green onions are a must-grow in our Desert Southwest gardens. They add a fresh, mild onion flavor to everything from tacos to salads, and nothing beats the satisfaction of snipping them straight from your garden. Plus, they're super versatile and thrive in our two growing seasons.

Sure, desert gardening has its challenges—extreme heat and alkaline soil, for starters. But with a little planning, you can enjoy a continuous harvest of green onions nearly year-round thanks to our long 313-day growing season. Timing is key, and the green onion is a forgiving crop.

If you're starting green onions from transplants, aim to get them in the ground during the cooler months, from early January through early February. This gives them a chance to establish before the extreme heat kicks in.

Before transplanting, harden off your seedlings by gradually exposing them to the outdoor conditions for about a week. This helps them adjust to the desert sun and lower humidity.

Plant them 2-3 inches apart in well-draining soil. Keep an eye on the weather and protect young transplants from any unexpected temperature dips we sometimes see during this time of year.

Direct sowing is the easiest way to grow green onions here. You can sow seeds directly into the garden from early January through early October, taking advantage of our two growing seasons.

Prepare your soil by loosening it and adding some compost to improve drainage and fertility. Green onions prefer soil temperatures between 60-70°F for optimal germination. Sow seeds about ½ 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 soil, and they'll regrow.

Watering is critical for green onions in our arid climate. These guys need consistent moisture to produce tender, mild stalks. Their shallow roots can dry out quickly, especially during the extreme heat.

During the cooler months (late fall, winter, early spring), water deeply about once or twice a week, providing about 1 inch of water each time. In the peak of summer, you might need to water every day or every other day, especially if they're in full sun. The "finger test" is your friend – 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 in our monsoon season. Signs of underwatering include wilting and yellowing leaves, while overwatering can lead to rotting at the base. A light layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool.

You can expect your first harvest of green onions from early March through late December, about 60-70 days after planting. They're ready to harvest when the stalks are about pencil-thick.

To harvest, you can either pull up the entire plant or snip the green stalks about an inch above the soil line. Cutting them allows the plant to regrow, giving you a continuous harvest.

To keep them producing, harvest regularly. As our first frost approaches in mid- December, harvest any remaining green onions to use fresh or freeze for later.

Here are some common problems you might encounter with 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 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 adult flies from laying eggs near your plants. Apply beneficial nematodes to the soil to control the larvae.

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 quickly multiply in our arid climate.
• How to fix/prevent it: Regularly spray plants with a strong stream of water to dislodge thrips. Insecticidal soap or neem oil can also be effective.

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. Different species affect different plants. The monsoon season can create favorable conditions for this disease.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides for prevention. Plant resistant varieties where available.

Pink Root

• What it looks like: Pink or reddish roots, stunted growth, and yellowing leaves.
• What causes it: A soilborne fungus that thrives in warm, alkaline soils.
• How to fix/prevent it: Improve soil drainage and avoid overwatering. Rotate crops to prevent the buildup of the fungus in the soil. Amend the soil with organic matter to improve its health.

Desert Southwest Specific Challenges: The extreme heat and low humidity of our region can stress green onions, making them more susceptible to pests and diseases. The alkaline soil can also affect their growth. Be sure to provide adequate shade during the hottest part of the day and amend your soil with compost to improve its nutrient content and drainage. Monsoon rains can lead to fungal issues, so keep an eye out for signs of downy mildew and take preventative measures.

Green onions are great companions for several plants in our Desert Southwest gardens. Carrots benefit from the onion's pungent smell, which deters carrot root flies. Lettuce thrives in the partial shade provided by green onions, protecting it from sunscald. Tomatoes and peppers benefit from the pest-repelling properties of onions. Beets also appreciate the improved soil conditions around green onions.

Avoid planting green onions near beans and peas, as they can inhibit their growth. These legumes prefer different soil conditions and may compete for nutrients.