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A hilly predicament

Q: What’s the best way to plant a tree on a hillside?

Roger Burnett, Adams, MA

Simple Steps for Hillside Planning Photo/Illustration: Haley Aselin Graves

A: Melissa LeVangie, certified arborist and owner of Trees New England in South Handley, Massachusetts, responds: Planting on hillsides can be tricky for both the planter and the planted. The tactics for planting trees and shrubs on hillsides, however, are not very different from those for planting on even ground. In both cases, the roots of existing vegetation are the glue that holds the soil together. The difficulty in hillside planting stems from the instability of the soil once the slope is disturbed. Preparing your site properly will help establish the tree’s root system, which, in turn, will help stabilize the soil.

It’s also important to choose your tree carefully. One that can withstand fairly anaerobic conditions will adjust well to the relatively harsh environment. Trees that work well on hillsides include red maples (Acer rubrum and cvs., Zones 3–9), sycamore maples (Acer pseudoplatanus and cvs., Zones 4–7), sycamore (Platanus occidentalis, Zones 5–8), pin oaks (Quercus palustris and cvs., Zones 5–8), swamp white oak (Quercus bicolor, Zones 4–8), and serviceberry (Amelanchier canadensis, Zones 3–7).

Once you’ve selected the desired location, prepare the planting site by creating a back-sloped cut into the hillside. Use the edge of a shovel or a Pulaski (an excellent cutting tool that combines an ax head on one side and a flat spade on the other) to cut at an angle into the slope. This will make a solid platform for the tree’s root-ball and help stabilize the planting area.

Reinforce and widen the planting platform by transferring soil and organic matter to the lower part of the slope. The platform should be wide enough to accommodate your new tree. Dig a planting hole that is two to three times the size of the root-ball, and place the tree at the proper height, keeping the trunk flare visible.

Remove as much of the basket and burlap as you can from the top two-thirds of the root-ball. Backfill the soil, and create a strong well of soil around the tree about 12 inches away from the trunk. The well acts as a raised, circular moat, which retains water that will slowly seep into the soil rather than run off before the tree has a chance to absorb it. Apply a 3- to 4-inch-deep layer of mulch onto the well. Make sure the mulch is level and away from the trunk of the tree. The mulch will ensure greater water retention after planting.

Staking is no longer generally recommended, but if your hilly site is windy, you’ll want to stake the tree to keep it stable as the roots become established. Keep the stakes away from the lower branches and trunk. The stake ties I prefer are ArborTie or Aglock. Both products are trunk friendly and easy to use. Once the ties are in place, the tree’s trunk should be able to sway and gently bend. Monitor the tree to be sure bark is not being rubbed off, and remove staking after one to two years.

Most newly planted trees and shrubs that die do so because of improper planting and poor post-planting care. For excellent information on tree planting and care, visit www.treesaregood.com.

From Fine Gardening 105, pp. 74