News Release Distributed 01/29/10

By LSU AgCenter Horticulturists Dan Gill, Allen Owings and John Young

Landscape beds, parking lots and construction activities around trees are all possible without harming the trees if you understand where the tree roots are and what they need to survive. Louisiana celebrated Arbor Day earlier in January, and now is a good time of the year to be reminded about tree care in landscape beds, parking lots and construction sites.

A tree’s important feeder roots are located in the surface soil and radiate out in all directions far beyond the crown spread of the tree. To survive, roots need oxygen, adequate moisture and organic soil components. Fill dirt, soil compaction, soil contaminants and damaging or cutting roots will kill trees.

Use the following guidelines to protect trees in potentially damaging situations:

Landscape beds

– Use a coarse organic soil mix when constructing beds around trees. Do not use any soil mix that has clay or silt in it.

– Do not till or dig up the existing soil around the tree.

– Only dig the holes necessary to install landscape plants.

– Do not install plants within two feet of the trunk or root collar of the tree.

– Install irrigation in beds around trees very carefully. Do not cut through feeder roots to install irrigation pipes. Do not arrange sprinkle heads so that water hits the trunk of the tree.

– Select drought-tolerant plants for beds under trees. Some landscape plants require more water than most trees. Irrigate as little as possible.

– Check the irrigation system often and fix leaks immediately.

Parking lots

– Use tree species that are tolerant of heat and root restrictions. Consider the growth form of tree selections. Live oak and Chinese elm, both popular selections for parking lots, have low-spreading forms that require almost constant pruning. Some trees such as bald cypress have roots or “knees” that can be a problem in parking lots.

– Root barriers or deflectors can be installed to prevent roots from lifting or otherwise damaging parking surfaces.

– The critical soil space for a tree in a parking lot is 100 square feet with a 5-foot minimum width.

– On average, street trees and parking lot trees have a life span of approximately 12 years. In concrete or asphalt parking lots, a minimum of 400 square feet (20 feet x 20 feet) planting area for each tree is necessary for healthier, more long-lived trees.

– Porous parking lots made of gravel, limestone or grass pavers are much better for trees because the roots can survive under the parking lot and are not as restricted by the size of the planting space.

Construction sites

– The first thing that should be done to protect trees in a construction area is to communicate with the construction crew and educate them about protecting the trees from construction activities.

– Protect the critical root zone with a fence completely around the tree. The critical root zone is equal at minimum to the crown spread of the tree. A fence is more substantial and works much better than flagging. Monitor the fence often to make sure everyone understands to leave the fenced area alone.

– Before construction begins, treat the critical root zone area by aerating the soil, applying a root stimulator and mulching. This should continue for a year after construction.

– Do not trench for electrical, water, sewer, gas or any other reason in the root zone.

– Do not grade, fill or otherwise disturb the soil in the root zone.

– Do not park vehicles or heavy equipment or store materials within the fenced area.

– Do not dump concrete, drywall, paint or any other material in the root zone.

– Do not attach signs or otherwise damage the trunk or branches.

– Do not allow anyone except an arborist to prune the tree for any reason.

– Do not take down the fence until all construction is finished.

Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.louisianahouse.org and www.lsuagcenter.com/lyn.

Rick Bogren