Green Onions in Zone 6A — Mountain West

Green onions are a must-have in any Mountain West garden. Their mild, fresh flavor adds a zing to everything from salsas to stir-fries, and they're incredibly versatile. Plus, in our high-altitude gardens, the cool nights even in summer help develop a sweeter, less pungent onion flavor.

Our short 153-day growing season and intense sun can be a challenge, but green onions are quick to mature and relatively unfazed by our temperature swings. With a little attention to watering and timing, you'll have a steady supply.

You can transplant green onion seedlings outdoors from early April through early May. This gives them a head start, especially if you're after an early harvest. Before planting, be sure to harden off your seedlings by gradually exposing them to the outdoor elements for about a week.

Plant them 2-3 inches apart in rows. Keep an eye on the weather forecast, as late frosts are common in the Mountains. Be ready to cover your transplants with frost cloth if a cold snap threatens.

Direct sowing is the easiest way to grow green onions here. Sow seeds from early April through mid July for a continuous harvest. Prepare your soil by loosening it and adding compost, especially if your soil tends to be alkaline.

Plant seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until they germinate. For an even easier start, 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, especially with our dry Mountain air. Aim to keep the soil consistently moist, but not waterlogged, for the best flavor and growth. The shallow roots can dry out quickly in our intense sun and low humidity.

During the peak of summer, when temperatures are in the 80s, you'll likely need to water deeply about 2-3 times per week, providing about 1 inch of water each time. Use the finger test: if the top 2 inches of soil feel dry, it's time to water. Water at the base of the plants to avoid splashing soil onto the leaves, which can help prevent disease.

In the cooler spring and fall months, you can reduce watering to once or twice a week. Watch for signs of underwatering, like drooping or yellowing leaves. Overwatering can lead to rot, so ensure good drainage. A light layer of mulch, like straw or shredded leaves, can help retain moisture and regulate soil temperature.

You can expect your first harvest of green onions starting in early June, and continue harvesting through early October. They're usually ready about 60 days after planting, when the stalks are about pencil-thick. Don't worry about a specific size; harvest them when they look good to you.

To harvest, you can either pull the entire plant or cut the stalks about an inch above the soil line. If you cut them, they'll often regrow, giving you multiple harvests. As the first frost approaches in early October, 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 Mountain West:

Onion Maggots

• What it looks like: Wilting or yellowing plants, stunted growth, and small white maggots feeding on the roots.
• What causes it: These pests are attracted to onions and lay their eggs at the base of the plants.
• How to fix/prevent it: Use row covers to prevent the adult flies from laying eggs. Introduce beneficial nematodes to the soil.

Thrips

• What it looks like: Silvery or white 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.
• 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 red, and plants become stunted.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Ensure good soil drainage. Rotate crops to avoid buildup of the fungus in the soil.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can actually help reduce the risk of some diseases that thrive in humid climates. However, our intense sun can stress plants, making them more susceptible to pests. Be vigilant about watering and provide shade during the hottest part of the day if needed.

Green onions play well with others in the garden. Carrots are great companions because the smell of onions deters carrot root flies. Lettuce benefits from the shade provided by green onions, which helps prevent bolting in the summer. Tomatoes and peppers also benefit from the pest-repelling properties of onions. Beets are good companions as well, as they don't compete for the same nutrients.

Avoid planting green onions near beans and peas. Onions can inhibit the growth of these legumes.