Green onions are a popular and versatile addition to many home gardens, prized for their mild flavor and continuous harvest. These slender, leafy vegetables are relatively low-maintenance. Understanding how green onions tolerate varying degrees of cold is key to ensuring a consistent supply throughout the growing season and even into colder months.
Green Onion Cold Hardiness
Green onions exhibit a notable tolerance to cold temperatures. While they thrive in moderate temperatures between 60-75°F (15-24°C), many varieties are frost-tolerant and can endure temperatures well below freezing. Some varieties are even cold-hardy down to -10°F (-23°C) when well-established in the garden.
A light frost, typically occurring when temperatures dip just below 32°F (0°C), might cause some wilting or browning of the green tops. However, the plant’s root system usually remains unharmed, allowing for quick recovery and new growth once warmer conditions return. Conversely, a hard frost, where temperatures drop significantly to 28°F (-2°C) or lower for extended periods, can cause more extensive damage to the foliage. If the exposed portions of the bulbs appear translucent or water-soaked, this indicates freeze damage. Despite top-growth damage, green onions often possess the ability to regrow from their protected roots.
Protecting Green Onions from Frost
To protect green onions during cold snaps, apply a layer of organic mulch, such as straw, pine needles, or grass clippings, around the base of the plants. A layer of mulch, ideally at least 2 inches deep, insulates the soil and helps retain warmth around the roots.
Adequate soil moisture also plays a role in frost protection, as moist soil retains heat more effectively than dry soil. Watering green onions thoroughly before a predicted frost can help keep the soil warmer around the root system. Additionally, covering plants with frost blankets, row covers, or even old blankets can provide an extra layer of defense against freezing air. These covers should extend to the ground to trap heat and protect the foliage from direct exposure to cold winds.
Post-Frost Care and Harvesting
If green onions have been exposed to frost, assess the damage. Severely damaged, mushy, or discolored foliage should be trimmed away. Despite visible top damage, the underground root systems are often resilient and can resprout new greens. Allow a couple of weeks for the plants to generate new carbohydrates and show signs of recovery, indicated by emerging new leaves.
Green onions can be continuously harvested throughout the growing season. If a hard frost is anticipated, harvesting the entire plant before the cold arrives is an option. After a light frost, green onions are generally safe to harvest and consume; some even suggest that light frost can enhance their flavor by converting starches into natural sugars. When harvesting, snip the leaves about an inch or two above the soil line, allowing the plant to regrow for future harvests.
Overwintering Green Onions
Green onions can often be overwintered in the garden for continued harvests in spring. Many varieties are hardy enough to survive winter in USDA zones 6 through 9, and sometimes even colder regions with proper protection. A thick layer of mulch applied in late fall is a primary method for overwintering, protecting the bulbs from freezing temperatures and allowing them to go dormant. This mulch should be removed in early spring as the soil warms, encouraging new growth.
For gardeners in colder climates or those with limited garden space, growing green onions in containers offers flexibility. Containers can be moved indoors to a sunny window or a protected area like a garage or unheated shed during the coldest months. While indoor conditions may slow growth, it can provide a fresh supply throughout winter. Alternatively, leaving green onions in the ground to go dormant is a common practice, with plants often being among the first to produce new shoots as spring arrives.