Trees in Raised Beds

Raised bed gardens, or garden beds constructed above natural terrain, benefit both trees and gardeners. Raised beds add a variety of heights, textures and contrasts to please the eye. Functionally, higher, easy-to-reach raised beds provide better ergonomics. Soil in raised bed drains more effectively, heats up earlier in the spring and prevents root exposure to poor soil. With a bit of planning, landscape and fruit trees can thrive in raised beds.

The most basic raised garden bed is the ground bed. Raised ground beds consist of sloped, 6- to 8-inch mounds of soil mixed with compost, peat moss or manure. Ground beds should measure between 2 1/2 and 5 feet wide. Surround the ground beds with access areas at least 24 inches wide. Ground beds are appropriate for smaller tree species.

Larger trees may require more space than raised ground beds can afford. Surrounding structures made from wood, plastic, rock or brick surround supported raised beds. Supported raised beds can be larger than 5 feet wide. The University of Minnesota recommends using untreated, rot-resistant wood such as cedar to construct a support structure. Once boards are connected with deck screws, fill in the bed with amended soil. Supported raised beds can accommodate larger tree species as no sloping is necessary at the bed’s edge.

Many tree species cannot tolerate poorly drained, soggy soils. According to North Carolina State University’s Cooperative Extension Service, it’s always better to plant trees in a raised manner than planting too deep and risking exposure to saturated soil. Common landscaping trees especially susceptible to waterlogged soil include flowering dogwood (Cornus florida), white fir (Abies concolor), sugar maple (Acer saccharum) and white pine (Pinus strobus). Raised beds can help eliminate damage from wet soil. When planting landscaping trees in raised bed, planting depth is the most important consideration. To plant in a 10-inch-high raised bed, dig a hole the same depth and two to three times as wide as the tree’s root ball. After filling in the hole, the North Carolina State University Cooperative Extension Service recommends forming a 4- to 6-inch soil barrier around the tree’s drip zone to minimize runoff.

Poorly drained soil poses a special risk to fruit trees such as cherries, peaches and nectarines. Raised bed planting offers a solution to this problem, as raised beds dry out faster and offer better drainage. Beds should be at least 6 to 8 feet wide and 8 to 10 inches high. The University of Ohio recommends amending the soil with organic matter before planting and applying 1 to 2 inches of mulch to the bed’s surface.

Though it can be a challenge, you can incorporate an existing tree into a new raised bed. The Texas A&M Agri-Life Extension recommends placing a circle of metal edging around the tree to keep soil and mulch away from the trunk. Leave as much space as possible between the edging and the tree trunk. Don’t add too much soil on top of established tree roots, though, as this can damage or even kill plants.