The importance of planting trees at the correct depth
A few years ago, Mike saw a Lime gently rocking in the soil, its trunk leaving an ever-increasing hollow in the soil line, signifying that its root system is buried way below the correct level. It is widely recognised that planting trees too deep is a major cause of premature decline.
Tree roots need oxygen and water blended in measure, so they inevitably grow within the top metre of the soil. Plant the container an inch proud of the soil line — it’ll settle down naturally as the ground adjusts. Better to plant too proud than too deep!
Root-balled trees can be quite problematic. When these trees are grown and lifted in the field, soil is often pushed up around the stem, meaning they start off sitting several inches too deep. Some nurseries then pot these trees into containers, adding even more compost on top. Later, landscapers may install them using root anchors for stability, without adjusting the planting depth. As a result, many root-balled trees end up planted at least five inches too deep—a major cause of failure later on.
The design of the planting pit is another common issue. We often speak to landscape architects who specify a standard 1.2-metre square pit—but why make it so deep? When the soil beneath the tree is loosened, the tree tends to sink into it, especially if it’s being pulled down by a root anchor. This leaves the roots sitting in compacted soil with little to no oxygen—a poor environment for healthy growth. What a tree really needs is width, not depth.
Professor Gary Watson, who has studied this issue in the USA, uses the term ‘root shank’ to describe the section of the tree’s stem below ground, before the root system begins. A helpful way to visualise this is to think of a fine red wine glass—with a slender stem, a flat base, and a wide bowl. This mirrors how a tree stands firm: the broad base provides stability. If the base isn’t wide enough, the tree is easily blown over. And if it’s planted too high up the stem, it tends to wobble and shift in the soil.
When we lift our large trees from the field and pot them, the top of the first root is placed no more than a centimetre below the compost surface. For customers who request it, we also mark the point where the root flare meets the compost with a line
This simple visual guide helps ensure correct planting depth: if the paint line isn’t visible after planting, the tree has been set too deep. We call this ‘The Barcham Line’, and we hope it becomes a valuable tool in tackling the all-too-common—and damaging—practice of planting trees too deep.
See how we recommend planting our trees in our video on ‘how to plant a Barcham Tree’: