Green Onions in Zone 3B — Mountain West

Green onions are a must-grow in our short Mountain West season. Their fresh, mild 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 garden for dinner, even with our cool nights.

Our high altitude and intense sun can be tough, and our growing season is definitely short, but green onions are quick to mature. With a little attention to timing, you can easily harvest plenty of these flavorful alliums within our 108-day window.

You can transplant green onion seedlings outdoors from late April through late May, after the risk of hard frost has passed. Before planting, be sure to harden off your seedlings. Give them about a week of gradually increasing outdoor exposure to acclimate them to our intense UV and cooler temperatures.

Space transplants about 2-3 inches apart in rows. Keep an eye on the weather forecast, as we can still get unexpected cold snaps or even hail during this period. Be ready to cover your young plants if needed.

Direct sowing is the easiest way to grow green onions here. Sow seeds from late April through late June. They'll germinate best when the soil temperature is consistently above 50°F, so wait until the soil has warmed up a bit.

Prepare your garden bed by loosening the soil and adding compost to improve drainage and fertility. Plant seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until the seedlings emerge. As a bonus, 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 produce tender, mild stalks, but it can be a tricky balance here with our dry climate. They're definitely not drought-tolerant. Aim to keep the soil consistently moist, but not waterlogged.

During our warmer summer months, from late June through August, you'll likely need to water deeply about 1-2 times per week, providing about 1 inch of water each time. Use the finger test – stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases.

In early spring and late summer, when temperatures are cooler, you can usually reduce watering to once a week or less. Signs of underwatering include yellowing leaves and stunted growth. Overwatering can lead to root rot, so watch for wilting or mushy stalks. A light layer of mulch, like straw or wood chips, can help retain moisture in our dry air.

You can expect your first harvest of green onions from late June through mid September, about 60-70 days after planting. The best time to harvest is when the stalks are about pencil-thick.

You can either pull up the entire plant or cut the stalks off about an inch above the soil line. If you cut them, they will often regrow, giving you a continuous harvest. For continued production, be sure to water and fertilize regularly after harvesting.

As our first frost approaches in early 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 a bit longer.

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

Onion Maggots *What it looks like:* Wilting or yellowing plants, stunted growth, and small white maggots feeding on the roots and bulbs. *What causes it:* These pests are attracted to onions and other alliums. The flies lay their eggs near the base of the plants, and the maggots hatch and burrow into the roots. *How to fix/prevent it:* Use row covers to prevent the flies from laying eggs. You can also apply beneficial nematodes to the soil to control the maggots.

Thrips *What it looks like:* Silver streaks or blotches on the leaves, distorted growth, and tiny, slender insects on the plants. *What causes it:* Thrips are tiny, sap-sucking insects that can damage plant tissue. They thrive in hot, dry conditions, which we often have here. *How to fix/prevent it:* Keep plants well-watered and use insecticidal soap or neem oil to control infestations. 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. Different species affect different plants. *How to fix/prevent it:* Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides for prevention. Plant resistant varieties where available.

Pink Root *What it looks like:* Pink or reddish roots, stunted growth, and yellowing leaves. *What causes it:* A soilborne fungus that infects the roots. It's more common in warm, wet conditions, but can still occur in our alkaline soils. *How to fix/prevent it:* Improve soil drainage, rotate crops, and avoid overwatering. Soil solarization can help reduce the fungus in the soil.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can actually be beneficial for green onions, as they reduce the risk of many fungal diseases. However, the intense sun can sometimes scorch the leaves, so providing some afternoon shade can be helpful. Our alkaline soil can also be a challenge, so amend with compost to improve nutrient availability.

Green onions are great companions for many plants in the Mountain West garden. Carrots benefit because the onion scent deters carrot root flies. Lettuce thrives nearby because green onions repel aphids. Tomatoes and peppers enjoy the protection from various pests that green onions provide. Beets do well, as green onions can deter leaf miners.

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