Green Onions in Zone 9A — Desert Southwest

Green onions are a must-grow in our Desert Southwest gardens. They're incredibly versatile in the kitchen, adding a mild oniony flavor to everything from tacos to soups. Plus, there's nothing quite like the satisfaction of snipping fresh green onions from your own backyard, especially when you know they're thriving despite our challenging climate.

Sure, desert gardening comes with its hurdles, like extreme heat and alkaline soil. But with a little planning and attention to timing, you can easily grow green onions during our two growing seasons. Our long 298-day season gives you plenty of opportunities for planting and harvesting.

If you're starting green onions from transplants, aim to get them in the ground from mid-January through mid-February. This gives them a head start before the weather really heats up. Make sure to harden off your seedlings for about a week, gradually exposing them to the outdoor conditions, including our intense sun, before planting.

Space your transplants about 2-3 inches apart. Keep an eye on the weather forecast around transplant time. Even though we're generally frost-free by late February, an unexpected cold snap can still happen.

Direct sowing is the easiest way to grow green onions here. You can sow seeds from mid-January through late September. Choose a spot with full sun to partial shade, especially for summer plantings when afternoon shade is beneficial.

Prepare the soil by loosening it and amending with compost to improve drainage and fertility. Sow seeds about ¼ inch deep, spacing them 2-3 inches apart. Keep the soil consistently moist until the seeds germinate, which usually takes about a week or two. Don’t forget you can also plant the root ends of store-bought green onions – a quick and easy way to get a continuous supply!

Consistent moisture is key to growing tender, mild green onions in our arid climate. They have shallow roots, so they dry out quickly, especially during the extreme heat of summer. Aim to keep the soil consistently moist, but not waterlogged.

During the cooler months (late fall through early spring), you'll likely only need to water once or twice a week, providing about 1 inch of water each time. As temperatures rise in late spring and summer, increase watering to every other day, or even daily during the hottest stretches, providing up to 2 inches of water per week. Use the finger test: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. When the monsoon season hits, adjust your watering schedule based on rainfall.

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, so be sure your soil is well-draining. A layer of mulch, like straw or wood chips, can help retain moisture and regulate soil temperature.

You can expect your first harvest of green onions about 60-70 days after planting, typically from mid-March through mid-December. Look for stalks that are about pencil-thick. You can either pull the entire plant or cut the stalks about an inch above the base.

Cutting above the base allows the plant to regrow, giving you a continuous harvest. For ongoing production, snip off the flower stalks as they appear to prevent the plant from going to seed. As the first frost approaches in early December, harvest any remaining green onions to enjoy before the cold weather sets in, or cover them to extend the season a bit longer.

Here are some common problems you might encounter with green onions in our region:

Onion Maggots

• What it looks like: Wilting or yellowing leaves, stunted growth, and small white maggots feeding on the roots and bulb.
• What causes it: These pests are attracted to the onion family.
• How to fix/prevent it: Use row covers to prevent adult flies from laying eggs near your plants. Introduce beneficial nematodes to the soil.

Thrips

• What it looks like: Silvery or distorted leaves with tiny black specks (thrip droppings).
• What causes it: These small insects suck plant juices, causing damage. They thrive in hot, dry conditions.
• 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: 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 plants may be stunted or wilted.
• What causes it: A soilborne fungus that thrives in warm, wet conditions.
• How to fix/prevent it: Improve soil drainage and avoid overwatering. Rotate crops to prevent the fungus from building up in the soil.

Desert Southwest Specific Challenges: The extreme heat and intense sun can stress green onions, making them more susceptible to pests and diseases. Our alkaline soil can also affect nutrient uptake, so amending with compost is essential. The monsoon season can bring periods of high humidity, which can increase the risk of fungal diseases like downy mildew.

Companion planting can really boost your green onion crop. Carrots are great companions because they deter onion flies, while the onions deter carrot root flies. Lettuce thrives in the shade provided by green onions, and green onions can help repel aphids that target tomatoes and peppers. Beets also benefit from being planted near green onions, as the onions can help deter leaf miners. Avoid planting green onions near beans and peas, as they can inhibit each other's growth.