PREPARING THE PLANTING HOLE Technical information and practices for planting new trees Prepared by CropHealth Advising & Research Kelowna BC Canada www.crophealth.com
Size of the planting hole Dig a shallow, broad planting hole but only as deep as the root ball. Drawing from Introduction to Arboriculture: Planting and & Early Care CD. 2006. International Society of Arboriculture Roots will grow away from the root ball into the wide planting hole. It is better not to disturb the soil under the root ball. These practices provide wide space for root growth and stability to prevent tree settling.
Planting hole width The planting hole should be two to three times as wide as the root ball. Trees benefit from wider planting holes, especially on sites with compacted or slow draining soil. In many urban soils, root growth from the bottom half of the root ball will be minimal. Loosened soil around the root ball provides greater soil volume for rapid initial root growth. Drawing from Plant Health Care for Woody Ornamentals Page 46 (1997) University of Illinois Board of Trustees and the International Society of Arboriculture The success of a tree is fundamentally linked to the soil in which it grows. James Urban
Sides of planting hole Roughen the sides of the hole to break the interface and help root penetration. Drawing from Best Management Practices Tree Planting. 2005. International Society of Arboriculture Or, dig a hole wide enough for the root ball and place the tree. With a shovel slope the edges of the planting hole and tamp the soil firmly (but lightly) around the root ball.
Planting hole depth Adjust the depth of the planting hole to match the soil and local weather. Drawing from James Urban. 2008. Up By Roots Healthy Soils and Trees in the Built Environment. Page 419. International Society of Arboriculture Drawing 1 In a slow draining soil, plant the tree slightly higher. Drawing 2 In a well drained soil, the top of the root ball is level to the final grade. Drawing 3 In a dry climate, the root ball can be placed slightly lower.
Soil volume requirement Use a long, trench-like planting hole in areas where the soil width is limited. The soil volume must be large enough to support the size of the mature tree. This consideration is important when planting near sidewalks and roadways.
Limited horizontal area for root growth Increase soil depth in areas with limited width. For trees, the minimum soil depth should be 0.75 to 1 metre. Loosened soil Root ball Compacted soil The soil under the root ball should be undisturbed or compacted to reduce future settling. A deeper soil with an improved structure will retain water longer. This feature will be important where the horizontal soil profile is thin, the soil is sandy or the site is designed for low maintenance. Drawing adapted from James Urban. 2008. Up By Roots Healthy Soils and Trees in the Built Environment. Page 204. International Society of Arboriculture
Limited planting space Plant trees appropriate to the planting area. The volume of soil available must be large enough to support the size of the mature tree. In a small planting space consider planting a smaller tree.
Backfilling Firmly but lightly tamp the backfill soil around the base of the root ball. Excessive tamping can compact soil and slow water penetration and root growth. Do not grade when the soil is wet. On sites with high-quality soil, use the native soil to backfill the planting hole. On sites with low-quality soil, use compost as an amendment to mix with the backfill soil. Compost added to the planting hole can be 10% to 40% of the total soil volume. However, an excessive amount of compost can cause soil shrinkage and settling of the tree.
Soil amendment Use properly composted plant material as an organic amendment. Better quality compost is the color of dark chocolate with a pleasant smell. Bark chips are good for surface mulch to reduce weeds and keep grass away.
Industry Standards Roots and Planting Excavation of the subgrade below the root ball shall permit the bottom of the root ball to sit on undisturbed material or compacted fill such that the top of the root ball remains at the proper finished grade. The British Columbia Landscape Standard (2008) British Columbia Society of Landscape Architects & and British Columbia Landscape & Nursery Association Consider amendments only on sites with poor-quality soil to improve soil structure, water-holding capacity, or drainage. Amending the whole planting site is preferred. Best Management Practices Tree Planting (2005) International Society of Arboriculture
For more details, consult these publications Available from BCLNA (B.C. Landscape and Nursery Association) http://bclna.com/bc-landscape-standards/ Available from ISA (International Society of Arboriculture) http://secure.isa-arbor.com/webstore/ All text and pictures from CropHealth Advising & Research, Kelowna, B.C., www.crophealth.com