Green Onions in Zone 7A — Mountain West

Green onions are a must-grow in any Mountain West garden. Their fresh, mild flavor elevates everything from salads to grilled meats, and they’re incredibly versatile in the kitchen. Plus, there's nothing quite as satisfying as snipping a few green onions fresh from your garden on a cool summer evening here in the mountains.

Our high altitude, intense sun, and short growing season present unique challenges. But with a little planning, you can enjoy a steady supply of green onions throughout our 173-day growing season. The key is timing your plantings and choosing the right spot in your garden.

If you want to get a head start, you can transplant green onion seedlings outdoors from late March through mid April. Be sure to harden off your seedlings for about a week before transplanting. Gradually expose them to the outdoor elements each day to prevent shock.

When transplanting, space the seedlings 2-3 inches apart in rows. Keep an eye on the weather forecast during this time. Late spring snow or a hard frost are always possible in the Mountains, so be prepared to cover your seedlings if necessary.

Direct sowing is the easiest and most common way to grow green onions in our region. Sow seeds directly into the garden from late March through late July for a continuous harvest.

Choose a spot with full sun to partial shade and prepare the soil by loosening it and adding compost. Green onions prefer well-drained soil. Plant seeds about ¼ inch deep and 2-3 inches apart. You can also plant the root ends of store-bought green onions. Just stick the root end in the soil, and they'll regrow!

Green onions need consistent moisture to thrive, but they don't like soggy soil. The key is to find the right balance, especially with our dry mountain air. During the warmer months, check the soil moisture regularly using the finger test: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water.

Generally, green onions need about 1 inch of water per week, but this can vary depending on the weather. During hot, dry spells, you may need to water more frequently. Water at the base of the plants to avoid wetting the foliage, which can encourage disease in other regions. But with our low humidity, overhead watering isn't a huge concern here unless you see signs of fungal issues.

Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to root rot, which shows up as stunted growth and mushy roots. Applying 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 late May through mid October, about 60 days after planting. Look for stalks that are at least pencil-thick. This is when they have the best flavor.

To harvest, you can either pull the entire plant or cut the green onion stalks about an inch above the soil line. If you cut them, they'll usually regrow for another harvest. For continuous production, plant new seeds every few weeks.

As the first frost approaches in early October, harvest any remaining green onions. You can chop and freeze them for later use. Or, pot up a few plants and bring them indoors to enjoy fresh green onions throughout the winter.

Here are some common issues to watch out for with green onions in the Mountain West:

Onion Maggots

• What it looks like: Wilting or yellowing plants, especially seedlings. You might find small white maggots near the roots.
• What causes it: These pests lay eggs at the base of onion plants. The maggots then burrow into the bulbs and roots.
• 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 streaks or white patches on the leaves. The leaves may also be distorted or curled.
• What causes it: Tiny, slender insects that suck the sap from plant leaves. They thrive in hot, dry conditions.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings. Spray plants with insecticidal soap or neem oil.

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 the plant's growth is stunted.
• What causes it: A soilborne fungus that thrives in warm, wet conditions and alkaline soil.
• How to fix/prevent it: Improve soil drainage. Rotate crops regularly. Consider solarizing the soil to kill the fungus.

Mountain West Specific Challenges: Our intense sun can sometimes stress green onions, making them more susceptible to pests and diseases. The alkaline soil can also be a problem, so amend your soil with plenty of compost. Hail can also damage the leaves, so consider using row covers or planting in a sheltered location.

Companion planting can help your green onions thrive in the Mountain West. Carrots are a great companion because they deter onion flies. Lettuce benefits from the pest-repelling properties of green onions. Tomatoes and peppers also benefit from being near green onions, as they can help deter certain pests. Beets are another good companion, as they don't compete for the same nutrients.

Avoid planting green onions near beans or peas. These plants can inhibit each other's growth. The alliums in green onions can stunt the growth of beans and peas, so keep them separated in your garden.