The science of companion planting requires a harmonious relationship between two different plant species, but even plants that were recently removed from a site still leave their mark within the soil itself. It is possible that natural, leftover root toxins may harm a newly planted crop. Strawberries (Fragaria spp.) and onions (Allium cepa) seem like an unusual combination in the garden, but it is possible to grow your favorite sweet fruits where onions once resided.
Pathogen and Pest Interaction
Preferring a wide range of locations in U.S. Department of Agriculture plant hardiness zones 3 through 10, strawberries have a number of different pests and pathogens that attach to their foliage and cause dieback, from mites to harmful verticillium wilt. Unlike tomatoes and peppers, onions do not typically harbor verticillium wilt that decimates strawberry crops -- the soil should be free from this pathogen. However, onions infested with onion maggots may leave some of these pests in the soil. Before planting your strawberries, apply a pesticide to the soil if you observe any larvae in the ground.
Your onion's old planting location works well for cultivating strawberries -- both plants need well-drained soil with a full sunlight location. Adding approximately 2-inches of organic matter to the topsoil helps your strawberry roots grow strong for effective anchoring and moisture uptake. Your previous onion garden makes strawberry planting faster since you do not need to cultivate the area from scratch -- remove any remaining onion plant debris to allow ample strawberry spread throughout the patch.
Although onions are slow-growing vegetables, their final size creates a huge, future space for strawberry planting. With approximately 18 inches between each strawberry plant, you need a sizable garden for prolific fruit production. In fact, strawberry rootlets grow into the thousands as they populate the garden, and die back after only a few weeks but are constantly replaced. As strawberries propagate through natural, above-ground daughter plants, or runners, they use the surrounding onion patch as an open space for more growth. Alternatively, remove these runners and plant them in other previous onion gardens -- you will have a constant supply of strawberry plants throughout the growing season.
Consider planting your strawberries with onions at the same time, or interplanting, so that both plants benefit. For example, rapidly growing strawberries produce shade across the soil so that onions remain in their preferred cool climate. If mature enough, the onion plants may disguise the strawberry's sweet scent so that pests do not feed on the developing fruits. Overall, both plants work well in the same planting space or you may simply plant strawberries alone -- your soil is healthy and cultivated for high strawberry fruit yields.
- Sunset: How to Grow Strawberries
- Ed Hume Seeds: Companion Vegetable Gardening
- National Gardening Association: Companion and Interplanting
- Oregon Live: Fit Strawberries Into a Tight Space by Interplanting Them
- Cornell University Cooperative Extension: Companion Planting
- Cornell University: Strawberry Plant Structure and Growth Habit
- The Old Farmer's Almanac: Strawberries
- The Old Farmer's Almanac: Onions
- Brand X Pictures/Brand X Pictures/Getty Images