Dealing with Existing Plants, Trees and Surface Roots
As you consider the fate of existing plants, remember that some plants have deep roots or surface roots. You can find this entry in the Site Assessment for Better Gardens and Landscapes workbook, however it is added here because we are working on documenting Existing Plants and Trees in this week's assignment.
Moving & Removing Existing Plants & Trees
If you move or remove plants and trees with extensive root systems, it may take the better part of a day to dig them up. Other plants may require professionals with specialized equipment to move or remove them. The plants you decide to renew may need extensive pruning, staking, trellising, or reshaping.
Other poorly placed plants and trees may need to be removed. As trees grow to mature sizes, they take up more space and create more shade. Factor that in as you plan. With shrubs and woody vines, however, it is possible to manage their size by judicious pruning.
Rule of Thumb
A rule of thumb defines a tree protection zone as a circle around the trunk with 1 foot of radius for each inch of dbh (diameter at breast height) Avoid changing the grade or building walls, patios or other below-ground based construction projects in the tree protection zone. This rule-of-thumb is primarily for tree root protection. For instance, if you have a mature tree with a 12-inch dbh, avoid construction projects within 12 feet of the trunk.
Digging within this circle will do damage to the roots. In this example, tree roots may spread out in a circle as far as 12 feet from the trunk of the tree. Vegetable gardens, where the soil may be tilled annually, are best suited outside of the tree protection zone. Plants with extensive roots such as shrubs, perennials, and vegetables, will find sites under and near a tree challenging because they are in direct competition with tree roots. This mature spruce tree is in good condition but must be cut down or severely pruned. It is about 2 feet in diameter and is only 2 feet from the house. The roots will continue to grow and may damage the foundation.
Keep it Simple
When underplanting with grass or ground covers, grass plants have relatively small roots and may get spotty, with more and more bare spaces as a tree grows to maturity. Weeds, especially those that can tolerate dry, less fertile soil, may fill in. Shallow-rooted, shade-tolerant ground covers, such as barrenwort or bishop’s hat may survive for several years, but perhaps not permanently. Judicious watering and fertilizing helps, but the plan here is “less planting is better.”
If you are keeping a larger tree in place, the best approach is to mulch under it, especially if there are extensive roots and surface roots. However, if you must plant in a small space under a tree, keep it simple and at least avoid shrubs. Shallow rooted plants, like annuals or herbaceous perennials that can be replaced, if necessary, are a compromise.
Tree roots from the other side of a fence or near a property line can affect plantings in the garden you are assessing. When the tree is on a neighbor’s property, you cannot remove the tree, but do not ignore it either. It will influence your assessment and planning for the future.
Adapted from Site Assessment for Better Gardens and Landscapes, Charles P. Mazza
Additional Resources
CCE Rockland: Surfacing Tree Roots
Purdue University: What to do With Tree Surface Roots, Woodmansee (2024)
Wisconsin Horticulture: How to Deal with Surface Tree Roots, Alfuth (2024)
University of Nebraska: Landscaping around Established Trees, Cue, Josiah (2002)