Green Onions in Zone 5A — Mountain West

Green onions are a must-grow in our short-season Mountain gardens. Their mild, fresh flavor elevates everything from summer salads to grilled meats, and they're incredibly versatile in the kitchen. Plus, there's nothing quite like the satisfaction of snipping fresh green onions from your own backyard, especially when you know you grew them despite our challenging climate.

Sure, high altitude, intense sun, and our short growing season present some hurdles. But with a little planning and attention to timing, you can easily enjoy a continuous harvest of green onions from mid-June until our first frosts arrive in late September. Our 138-day growing season is plenty of time to get them in the ground and enjoy a great yield.

Transplanting green onions is a great option if you want a head start on the season. Aim to get your transplants in the ground from mid-April through early May, giving them plenty of time to establish before the heat of summer. Before planting, be sure to harden them off by gradually exposing them to the outdoors for about a week.

Space the transplants about 2-3 inches apart in rows. Keep an eye on the weather forecast; we can still get some late-season frosts during this period. If a frost is predicted, cover your transplants with row covers or blankets to protect them.

Direct sowing is the most common and easiest way to grow green onions here. You can start sowing seeds from mid-April through mid-July for a continuous harvest. Choose a spot with full sun to partial shade and prepare the soil by loosening it and adding some compost. Green onions prefer well-drained soil.

Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seeds germinate, which should take about a week or two. A little trick: you can also plant the root ends of store-bought green onions directly into the soil. They'll regrow!

In our dry Mountain climate, consistent watering is key to growing tender, mild green onions. They aren't drought-tolerant and their shallow roots mean they dry out quickly. Aim to keep the soil consistently moist, but not waterlogged.

During the cooler spring and fall, water deeply about once a week, providing about 1 inch of water. Increase watering to 2 inches per week during the hotter summer months. Use the "finger test" to check the soil moisture: 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 disease in other areas, though with our low humidity it is less of a concern.

Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to root rot, so watch out for soggy soil and stunted growth. A layer of mulch around your green onions can help retain moisture and keep the soil cool, which is especially helpful in our intense sun.

You can expect your first harvest of green onions from mid-June through early October, about 60-70 days after planting. They're ready to harvest when the stalks are about pencil-thick. You can either pull up the entire plant or cut the stalks about an inch above the base. If you cut them, they'll regrow, giving you multiple harvests.

For a continuous supply, harvest a few green onions at a time as needed, rather than harvesting all of them at once. As our first frost approaches in late September, harvest any remaining green onions. You can chop and freeze them for later use, or transplant them into pots and bring them indoors to extend your harvest.

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.
• What causes it: These pests are attracted to onions and related plants. The flies lay eggs at the base of the plants, and the maggots burrow into the bulbs.
• How to fix/prevent it: Use row covers to prevent the flies from laying eggs. Apply beneficial nematodes to the soil to kill the maggots.
• Thrips
• What it looks like: Small, silvery streaks on the leaves, distorted growth, and tiny black specks (thrip droppings).
• What causes it: Thrips are tiny insects that suck the sap from plants. They thrive in hot, dry conditions.
• How to fix/prevent it: Spray plants with insecticidal soap or neem oil. 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 may wilt.
• What causes it: Soilborne fungus that thrives in warm, wet conditions.
• How to fix/prevent it: Improve soil drainage. Rotate crops to avoid planting onions or related plants in the same spot for several years.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally reduce disease pressure, but intense sun can stress plants, making them more susceptible to pests. Be sure to provide adequate water and consider using shade cloth during the hottest part of the day.

Companion planting can help your green onions thrive. Carrots are great companions because their scent repels onion flies. Lettuce benefits from the shade provided by green onions, which helps prevent bolting in the summer. Tomatoes and peppers also benefit from green onions as they deter certain pests. Beets loosen the soil, which helps green onions grow.

Avoid planting green onions near beans or peas. They can inhibit the growth of these legumes.