Can onions survive winter for perennial growth?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.While plenty of onions will not survive a hard freeze, there are exceptions. My Egyptian walking onions have survived winters in Wyoming at -15°F (-26°C) under 6-inch (15 cm) deep mulch. Bulb onions like 'Walla Walla' will die with frost, while perennial onions will come back every year from the bulbils underground. It's good to know the variety of onions you are growing and what to expect for winter survival.
Cold-Hardy Varieties
- Egyptian walking onions survive to -30°F (-34°C)
- Bunching onions tolerate 10°F (-12°C) with protection
- Multiplier onions regrow for 3-5 years in zones 5+
Winter Preparation
- Apply straw mulch after first hard frost
- Mound soil 6 inches (15 cm) around plant bases
- Cover with burlap during polar vortex events
Spring Revival Care
- Remove mulch gradually as temps reach 40°F (4°C)
- Apply 5-10-10 fertilizer when new growth appears
- Divide bulb clusters every 3 years for vigor
We require a degree of care for container onions. I overwinter my container onions in unheated garages - and insulated pots. Wrap your containers in bubble wrap coverings and group them. Water them once a month; even dormant plants require moisture. In my 2022 experiment, I achieved an 80% survival using this method in zone 5.
Frost heave causes more damage to onions than being cold alone. I avoid this problem by planting onions in raised mounds facing south in Vermont. The slope helps drain away meltwater from the bulbs. I also use a mulch of evergreen boughs that creates even more air space to hold the soil gap and stabilize the temperature of the soil.
Read the full article: When to Plant Onions: Expert Guide for Perfect Bulbs
