Green Onions in Zone 4A — Mountain West

Green onions are a fantastic addition to any Mountain West garden. Their mild, fresh flavor elevates everything from summer salads to grilled dishes, and they're incredibly versatile. Plus, there's nothing quite like the satisfaction of snipping fresh green onions from your own backyard, especially when our intense sunlight helps them develop such a vibrant taste.

Our short growing season and cool nights can present challenges, but green onions are surprisingly resilient. With a bit of attention to timing and watering, you can easily enjoy a continuous harvest throughout our 118-day growing season.

If you're starting green onions indoors, aim to transplant them outdoors in late April through mid May. Before planting, be sure to harden off your seedlings. Give them about a week of gradual exposure to the outdoors, increasing the time each day.

Space your transplants 2-3 inches apart in rows. Keep an eye on the weather forecast, as late frosts are still possible during this period. Cover your young plants with horticultural fleece if temperatures are predicted to dip below freezing.

Direct sowing is the easiest and most common method for growing green onions here in the Mountain West. Sow seeds directly into the garden from late April through early July. Green onions aren't picky, but they do prefer well-drained soil.

Before planting, loosen the soil and amend with compost to improve drainage and fertility. Sow seeds about ¼ inch deep and 2-3 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. For a continuous harvest, sow a new batch of seeds every few weeks. You can also plant the root ends of store-bought green onions for a quick start!

Green onions need consistent moisture to thrive in our dry Mountain West climate. They aren't drought-tolerant, and their shallow roots can dry out quickly, especially with our intense sun. Aim to keep the soil consistently moist, but not waterlogged.

During the warmer months, especially from mid-June through August, you'll likely need to water your green onions deeply a couple of times a week. Use the "finger test" – if the top two inches of soil feel dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the foliage, which can encourage disease.

Signs of underwatering include wilting and yellowing leaves. Overwatering, on the other hand, can lead to root rot, indicated by mushy, brown roots and yellowing leaves. A layer of mulch, such as straw or wood chips, can help retain moisture and regulate soil temperature.

You can expect your first harvest of green onions from late June through late September, about 60-70 days after planting. They're ready to harvest when the stalks are about pencil-thick. Don't wait too long, or they can become tough.

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

As the first frost approaches in mid- 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.

Here are some common problems you might encounter with green onions in the Mountain West:

Onion Maggots

• What it looks like: Yellowing or wilting plants, stunted growth, and small white maggots feeding on the roots and bulb.
• What causes it: These pests are attracted to onions and other alliums.
• How to fix/prevent it: Use row covers to prevent the adult flies from laying eggs. Companion plant with carrots, as their scent repels the flies.

Thrips

• What it looks like: Tiny, slender insects that suck sap from the leaves, causing silvery or white streaks and distorted growth.
• What causes it: Hot, dry conditions favor thrips.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil if infestations are severe.

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, stunting growth and causing the plant to wilt.
• What causes it: A soilborne fungus that thrives in warm, wet conditions and alkaline soil.
• How to fix/prevent it: Improve soil drainage. Amend soil with organic matter to lower pH. Rotate crops to avoid buildup of the fungus.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally help reduce disease pressure on green onions, but our alkaline soil can contribute to pink root. Consistent watering is crucial to prevent stress from our dry climate, which can make plants more susceptible to pests and diseases. Hail can also damage foliage, so consider using row covers for protection during severe weather.

Companion planting can greatly benefit your green onions here in the Mountain West. Carrots are excellent companions because their scent repels onion flies, and the onions deter carrot root flies. Lettuce provides ground cover, helping to retain moisture in our dry climate.

Tomatoes and peppers also benefit from being planted near green onions, as the onions can deter certain pests. Beets are also good companions.

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