Green Onions in Zone 6B — Mountain West

Green onions are a must-grow in our Mountain gardens. Their fresh, mild flavor is fantastic in everything from summer salads to grilled dishes, and they add a zesty bite that store-bought onions just can't match. Plus, you can't beat the satisfaction of snipping fresh greens right outside your door, even with our cool nights and intense sun.

Our short growing season and alkaline soil can be a challenge, but green onions are surprisingly adaptable. With a little planning and attention to watering, you can enjoy a continuous harvest. Our 163-day growing season is plenty of time to get multiple crops of these flavorful alliums.

You can transplant green onion seedlings outdoors in late March through late April, once the soil is workable. Before planting, be sure to harden off your seedlings. This means gradually exposing them to outdoor conditions for about a week to toughen them up.

Space your transplants about 2-3 inches apart in rows. Keep an eye on the weather forecast at this time of year; we can still get some surprise snow or late frosts. Cover your young plants with row covers or frost blankets if a cold snap is predicted.

Direct sowing is the easiest way to grow green onions in our region. You can 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 well-drained soil.

Before sowing, amend your soil with compost to improve drainage and fertility. Green onions prefer a slightly alkaline soil, so you may need to add some lime if your soil is particularly acidic. Sow seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. A neat trick? Plant the root ends of store-bought green onions for a quick start!

Consistent watering is key to growing tender, flavorful green onions in our dry Mountain climate. While they aren't drought-tolerant, overwatering can lead to problems too. Finding the right balance is essential.

During the spring and fall, when temperatures are cooler, water deeply about once a week, providing about 1 inch of water. In the heat of summer, especially with our intense sun and low humidity, you'll likely need to water every other day, providing up to 2 inches of water per week. Use the "finger test" – 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, as this can encourage fungal diseases in our cool evenings. Yellowing leaves can indicate overwatering, while drooping or stunted growth suggests underwatering. A light layer of organic mulch, like straw or shredded leaves, can help retain moisture and regulate soil temperature.

You can expect your first harvest of green onions in late May through mid October, about 60 days after planting. They're typically ready to harvest when the stalks are about pencil-thick.

You can either pull the entire plant or cut the green onions off about an inch above the soil line. If you cut them, they will usually regrow for a second harvest. For continuous production, sow new seeds every few weeks throughout the growing season.

As our first frost approaches in early October, harvest any remaining green onions. They can tolerate a light frost, but prolonged freezing temperatures will damage them. 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: Yellowing or wilting plants, stunted growth, and small white maggots feeding on the roots.
• What causes it: These pests are attracted to the smell of onions and lay their eggs at the base of the plants.
• How to fix/prevent it: Use row covers to prevent the flies from laying eggs. Introduce beneficial nematodes to the soil. Remove and destroy any infested plants.

Thrips

• What it looks like: Small, elongated insects that feed on plant sap, causing silvery streaks and distorted growth on the leaves.
• What causes it: Thrips thrive in hot, dry conditions and can be blown in by the wind.
• How to fix/prevent it: Spray plants with a strong jet of water to dislodge thrips. Insecticidal soap or neem oil can also be effective. 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. Plant resistant varieties where available.

Pink Root

• What it looks like: Roots turn pink or reddish, and plants become stunted.
• What causes it: A soilborne fungus that thrives in warm, wet conditions.
• How to fix/prevent it: Improve soil drainage. Rotate crops to avoid planting onions in the same spot year after year. Plant resistant varieties. Solarize the soil in summer to kill the fungus.

Mountain West Specific Challenges: Our moderate-at-altitude summer heat and low humidity generally help to reduce fungal diseases. However, our dry conditions mean you'll need to pay close attention to watering to keep your green onions healthy. Hail can also damage the leaves, so consider using row covers or netting if hail is in the forecast.

Companion planting can help your green onions thrive. Carrots are excellent companions because their scent deters onion flies. Lettuce benefits from the shade provided by green onions, which helps prevent bolting in the summer heat. Tomatoes and peppers also benefit from green onions, as they repel certain pests. Beets are also good companions, as they don't compete for the same nutrients.

Avoid planting green onions near beans and peas. These legumes inhibit the growth of onions and vice versa.