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.
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.
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