BENEFICIAL LANDSCAPES: Lonely Trees how to help, and how not to
In our modern landscapes, trees often get planted as lone individuals surrounded by a sea of lawn. This is less than ideal for trees—and vice-versa. Trees typically grow in forests where little grass is present. When trees are placed in lawns and those lawns are excessively fussed over (and we Americans love to fuss over our lawns) trees can be sitting ducks for such things as mower and trimmer damage as well as herbicide injury. Another issue is underground as tree roots and lawn roots don’t always mix well. Lawn soils are often wet and compacted which favors grasses while tree roots prefer loose soils rich in microbial and fungal life.
This is too bad, because we can have both a nice, highly-functional lawn and healthy trees if we do it right. One place to start is by surrounding trees with companion plantings that create an island of landscape. Trees in landscape beds will suffer fewer conflicts with lawn care and the soils typically become more bioactive and sustaining for the trees and the other companion plants that share the rooting zone.
Tree islands can be small—such as a few perennials or groundcovers in the mulch ring around the tree. But generally speaking, the larger they are the more benefits they provide. Good companion plants include shrubs of all kinds, as well as many perennials, ornamental grasses and various groundcovers. When the trees are young, the companion plants should be sun-loving. But as the trees grow, the companion plantings can transition to more shade-tolerant types.
Another great benefit of island planting—especially big islands, is that they reduce the amount of inputs associated with lawncare including mowing, trimming, aerating, watering, fertilizing and pesticiding (is that a word?). As someone who abhors mowing, this is a big plus for me. However, less lawn does not necessarily mean less management time. Landscape islands do require ongoing work weeding, trimming, replanting, watering and sometimes re-mulching. That’s a willing tradeoff for me as I much prefer gardening to lawn care.
Do your trees a favor and use more of them as anchors to island plantings. Not only will your trees be healthier and grow faster, the companion plantings will increase insect and wildlife biodiversity, improve soil health, aid in stormwater infiltration, help with water conservation and add dynamic beauty that increases property value and perhaps even the envy of neighbors.
What not to do
It’s important not to change the grade around established trees when adding other plants around them. In the modern landscape, people often like to put borders of rock, timbers or concrete blocks around their trees to create a crisp separation between the two, and often the soil level within these borders is raised for planting annual or perennial flowers within them. There’s nothing wrong with a hardscape border around a tree or a landscape bed, but it’s important NOT to change the soil grade within those beds if they’re being constructed around existing trees.
Raising the soil level is the equivalent of planting the tree too deep, which can lead to serious root decline and potential tree death. Many people don’t realize that most tree roots grow within a few inches of the soil surface where they’re better able to exchange atmospheric gases and compete for soil nutrients.
A simpler solution that is better for trees is to establish an at-grade mulch ring around new trees and plant companion plantings directly within that mulch ring. There’s no need for hardscape edging.
For new trees, similarly, it’s best not to change the soil grade in a small area around the tree since their roots will eventually reach far beyond the base of the tree.
Justin Evertson, Nebraska Statewide Arboretum, plantnebraska.org