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Laid-Back Gardening with Robert Kourik

Laid-Back Gardening with Robert Kourik


Plant for fruitfulness — not your typical planting hole

Planting a tree seems easy enough; just dig an enormous hole, fill it up with lots of amendments, compost, and fertilizers, bind a stake to the trunk, water at the base of the trunk like there’s no tomorrow, and sit back. According to many recent studies, however, all this is literally overkill or just plain wrong.

When I was running a landscape business, I was amazed to discover over the years that the trees planted with the most amendments were the most likely to blow over, and that perfectly good-looking small perennial shrubs could be pulled out of the ground years after planting, their roots still conforming to the shape of the original planting hole. Many of the outdated planting guidelines about amendments continue to be praised with great fervor on radio and television gardening shows throughout the country. (It’s little surprise, since soil amendment companies are often some of the main sponsors of such radio programs.) They’re perpetuating profitable myths.

Thanks to research, we now know that proper planting begins by choosing the best rootstock or plant for your soil; that we needn’t use any amendments, compost, or fertilizers; that an actual planting hole may not be worthwhile (planting on a mound can be healthier); and that mulch shouldn’t be piled up against the trunk or stem of the plant.

The scoop on planting

Digging a hole seems like a simple task, but this is misleading. A poorly dug hole will have a detrimental effect for decades on any tree planted in it, and may even kill the tree.

Remember that the roots of most trees and shrubs will, if unrestricted, extend outward horizontally to cover an area 1.5 times wider than the canopy dripline in clayey soil, and up to 3 times wider in sandy soil. For a wonderful shade tree like a pin oak ( Quercus palustris) with a 40-foot spread, this means roots extending 60 feet across in clay soil and 120 feet across in sandy soil. The goal of planting is to encourage the tree’s or shrub’s roots to grow beyond the planting hole into the native soil as quickly as possible; thus, the size of even a well-dug hole has little influence on the growth of the tree. Dig a planting hole only when the soil is slightly moist, but not wet. Turning over a shovel full of wet clay soil causes the plate-like structure of the clay to compress, excluding air and further destroying what little loose structure the soil may have had. The result is a stickier and nearly anaerobic clay soil—a condition that’s tough on young root hairs. Sandier soils can be worked when they’re moister.

It’s important to remember to finish off the digging of the hole by using the spading fork to fracture the sides and bottom. This provides nooks and crannies that the young root hairs can use to creep out of the hole and into native soil.

I like to plant trees and shrubs on a mound for three important reasons: 1) The water drains away from the crown of the root system, preventing crown rots.

2) The roots are encouraged to grow away from the planting area in search of water and nutrients, thus creating a wider root system with more feeding root hairs. This makes for a healthier tree.

3) The wider the root system gets, the better the tree can stand up to wind, snow, and ice.

Photo by Anthony Pagani

Robert Kourik is the author of 18 books on gardening, including Lazy-Ass Gardening, Understanding Roots, The Insectary Calendar, and Drip Irrigation for Every Landscape and All Climates.