Planting in heavy soils
Heavy clay soils are one of the toughest environments to plant in, but there are no hard and fast rules to follow. Whether the planting site is irrigated or not, and how much irrigation it’s receiving is crucial information. Here is an example: Concolor Firs will often decline and die in a heavily irrigated clay soil. In a lightly irrigated setting they will do fine.
Many planting guides will tell you to excavate 2-3 times the root ball diameter and amend the soil with top soil and peat moss. This is a big mistake! When you do this in a heavy clay soil you create a large “bathtub”, which can fill up with water in a heavy rain and drown your trees and shrubs. Digging a hole just large enough to hold the root ball reduces the amount of water around the plant.
Planting a little or a lot high to grade, depending on how wet the soil is, can be a good defense strategy. Just use a well-draining topsoil to feather out from the top of the ball to the top of the surrounding soil.
This columnar oak was planted at a correct depth in a raised bed. See below for a closer view.
One of the biggest mistakes I see is planting trees above grade on the top of a berm. Trees subjected to this treatment will almost surely die! Any rain (other than an all-day soaker), runs right off the berm. In this case create a shallow basin and plant below grade to capture those quarter to half inch mini rains.
