How to Grow Perennial Potato Onions

These are some of these coolest onions out there. What makes them so amazing is mainly their storage longevity - up to eighteen months in ideal conditions. These onions produce clusters similarly to shallots, though they're larger and can stand in for onions in recipes in a way that shallots cannot. While they are smaller, one to three inches wide, they have a fantastic onion flavor. This is a great onion for the beginner gardener who struggles with starting onions from seed. These are replanted from the bulb which is generally considered easier. They are adapted to grow in a wide array of places, but will not grow well in Florida or Southern Texas. They can be replanted year after year and harvested each autumn. This means a perpetual supply of alliums for your kitchen without needing to start and baby onion seeds every single year. 

Growing Perennial Potato Onions

Perennial onions prefer well-draining soil high in organic matter in an area with full sun. Heavy clay soils may be best suited for raised bed gardening. Nitrogen should not be applied during bulb development (when the green shoots pop up), but the soil can always be amended with rock phosphate (for phosphorus and calcium)  or greensand (a soil conditioner that improves aeration and adds helpful trace minerals).

These onions are traditionally planted in the fall and are overwintered to give the roots a head start before spring. This will result in better bulb development and larger yields. Plant your potato onions 3 to 4 weeks before the first frost, around the same time as garlic. If you tend to have particularly harsh winters, consider mulching to protect your bulbs from dying. 

Space larger bulbs 6 to 8 inches apart and smaller bulbs 4 to 6 inches apart and ½ to 1 inch deep. The rows should be 12 inches apart from each other. 

Caring for Perennial Potato Onions

After you have planted the onions, water and cover with about 2 inches of mulch. If you experience a dry winter, be sure to keep the soil consistently moist. If the soil dries out, it will affect the bulbs’ development and the yield. 

Harvesting Perennial Potato Onions

It’s time to harvest when the onion tops fall over. After this happens, remove the mulch and stop watering for two weeks. Then, lift the onions out of the ground gently, with a garden fork. These perennial onions are dormant in summer and weeds will cause problems if they’re left in the ground to get overtaken. It’s better to harvest and replant in autumn. 

Dry them in a shady place in your garden or in a dry place - garages work great! Pick the more favorable onions to save for next year’s seed. These should be the largest onions without any blemishes and well formed skins. They will keep well in a cool, dry place.

	Article Written by: Hannah Gibbons
	About the Author: Hannah Gibbons, an employee at Sow True Seed since 2020, has nearly a decade of experience in the agricultural industry. Their passion for environmental education and regenerative agriculture has been the cornerstone of their work, aimed at making gardening accessible to all.