Green Onions in Zone 4B — Mountain West

Green onions are a must-grow for Mountain gardeners. Their mild, fresh flavor elevates everything from summer salads to grilled meats, and they're so easy to snip right from the garden. Plus, those cool nights we get even in summer concentrate their sweetness, making them extra delicious.

Our short season and alkaline soil can present challenges, but green onions are quick to mature. With a little planning within our 128-day growing season, you can enjoy a continuous harvest.

You can transplant green onions outdoors from mid April through mid May, giving them a head start. Be sure to harden them off for about a week by gradually exposing them to the intense sun and cooler temperatures. Plant them 2-3 inches apart in well-draining soil.

Keep an eye on the weather forecast, as late frosts are always a possibility. If a cold snap is predicted, cover your seedlings with frost blankets or row covers to protect them.

Direct sowing is the easiest way to grow green onions here. Sow seeds from mid April through early July, ensuring the soil temperature is at least 50°F. 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 white ends, roots down, into the soil, and they'll regrow. Keep the soil consistently moist, and you'll have fresh green onions in no time.

Green onions need consistent moisture to thrive, but our dry climate means they can dry out quickly. Aim to keep the soil consistently moist, but not soggy. Water deeply when the top two inches of soil feel dry to the touch – use the finger test!

During the hottest part of summer, you might need to water every other day, providing about an inch of water per week. Water at the base of the plants to avoid wetting the foliage, which can encourage disease, though with our low humidity, this is less of a concern than in other regions.

Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, indicated by wilting and mushy stalks. A light layer of mulch, such as straw or shredded bark, can help retain moisture and regulate soil temperature, which is especially helpful with our intense sun.

You can expect your first harvest of green onions starting in mid June and continuing through late September. They're usually ready about 60-70 days after planting, when the stalks are about pencil-thick.

To harvest, you can either pull the entire plant or cut the green onion above the base, leaving the roots in the ground. If you cut them, they will often regrow, giving you multiple harvests. As the first frost approaches in mid- September, harvest any remaining green onions, as they won't survive a hard freeze.

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

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. Rotate crops each year. Introduce beneficial nematodes to the soil.

Thrips

• What it looks like: Silvery streaks or white patches on the leaves, distorted growth, and tiny, slender insects visible upon close inspection.
• What causes it: Thrips are attracted to dry conditions and can be blown in by the wind.
• How to fix/prevent it: Keep plants well-watered. Spray plants with a strong stream of water to dislodge thrips. Insecticidal soap 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.
• 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 leaves may yellow and wilt.
• What causes it: A soilborne fungus that thrives in warm, moist conditions and alkaline soils.
• How to fix/prevent it: Improve soil drainage. Rotate crops. Amend soil with organic matter to improve its structure and nutrient content.

Mountain West Specific Challenges: Our intense sun can stress plants, making them more susceptible to pests and diseases. Low humidity can help prevent fungal diseases, but it also means you need to be extra vigilant about watering. Our dry rainfall also means you'll likely need to supplement with irrigation.

Green onions are great companions for many plants. Carrots benefit because the onion's scent deters carrot root flies. Lettuce enjoys the shade provided by green onions, which helps prevent bolting in our intense sun. Tomatoes and peppers benefit from the onion's pest-repelling properties. Beets also thrive alongside green onions, as they don't compete for the same nutrients.

Avoid planting green onions near beans and peas, as they can inhibit their growth.