The replacement price of a mature tree can exceed $20,000, so you need to do everything you can to protect trees during a turf conversion. A large, mature shade tree is the most valuable asset of any landscape and provides many important benefits. Trees reduce energy use by providing shade and evaporation cooling. They also add beauty, provide wildlife habitat, and sequester carbon. Not only is it smart to preserve these valuable trees, but it is the responsibility of adept owners and landscape professionals to protect these high-value assets.
Trees in the lawn
As trees adapt to growing in a lawn environment, they begin to rely on the uniform, frequent distribution of water applied to lawns through sprinklers. Additionally, the lawn and thatch layer help buffer temperature extremes, especially in hot, arid environments. Once established and happily growing in a lawn, any disruption to this environment (i.e. converting turf to xeriscape) can adversely affect tree health leading to stress, insect and disease infections, severe decline and eventual death.
The root of the issue
It is paramount that we understand the role of tree roots and the importance of protecting them. Tree roots store the energy needed to produce foliage, absorb water and fertilizer, produce important hormones, and act as an anchor to stabilize the tree. The majority of tree roots growing in urban lawns are found in the top 6 to 18 inches of soil. These roots consist of large perennial roots and small, short-lived feeder roots. The larger perennial roots stabilize and support the tree. The small feeder roots absorb water and nutrients and make up the majority of the root system near the soil surface. Feeder roots extend well beyond (up to 4 times) the tree’s drip line (see diagram) and are mixed with lawn roots. What are the consequences of damaged, cut-off tree roots? Water and nutrient absorption is eliminated, the tree’s stability is compromised, and the outcome is a decline, underperformance, and possible death.
The first lesson learned: Protecting a tree’s root system is crucial when performing turf to xeriscape conversions.
About the water
However, even when tree roots are left undisturbed the potential for great loss remains. With the lawn removed, roots left in the soil no longer have a temperature buffer and, more importantly, a water source provided by the lawn’s sprinkler system. Many beautiful and valuable shade trees have been lost because the new irrigation system failed to provide the correct amount of water to the correct area where it could be absorbed by feeder roots. At a minimum, the new irrigation system should provide coverage to 70% of the tree root zone (ideally 100%) to adequately meet tree water needs – remember, the tree root zone may extend 1 ½ to 4 times beyond the tree canopy.
The second lesson learned: Correct water management is not only about how much water is applied but where the water is applied.
The key to success is simple: protect the root system and provide adequate irrigation coverage
One of the most effective and efficient ways to meet tree water needs and ensure a long post-turf conversion tree life is to use subsurface, inline drip tubing. (For example, Total CV Emitterline or Top Drip Emitterline by Jain Irrigation, Inc.). The installation of this product is simple, minimizes damage to the existing root system, and provides trees with the right amount of water throughout the root canopy area. Organic or aggregate mulch should be applied, 2-4” deep, after the new irrigation system is installed to improve the aesthetic value of the landscape and to help reduce water loss to evaporation. The following recommendations will also help ensure success:
- Deeply irrigate trees during the entire conversion process to reduce stress and help ensure a successful transition.
- Identify and protect major roots near the soil surface. Removal of roots should be kept at an absolute minimum. Trenching under the canopy should be avoided, if possible, to minimize root damage. Consider tunneling under roots if absolutely necessary.
- Turf in the tree root zone should be removed carefully. This is best done using herbicides, a dethatcher, or a lawnmower to scalp the lawn to bare dirt. Heavy equipment and construction traffic will compact soil, crush roots and cause mechanical damage to the trunk, limbs, and roots.
- If a sod cutter, tractor or other heavy equipment will be used a protection zone or barrier should be set up around the tree canopy root zone to keep equipment at a safe distance.
- Water the tree to survive! Placing four drip emitters near the trunk of a mature tree is grossly insufficient. The new irrigation should provide water throughout the existing root zone and extend beyond to allow for future growth (ideally at least two times the diameter of the tree canopy). At a minimum, the new irrigation coverage should be 70% of the drip zone to sustain the tree and minimize stress.
Is it critical to protect tree root systems and provide proper irrigation (during and after) when performing turf to xeriscape conversions? Trees provide tremendous environmental, economic, and aesthetic value. Proper protection of and irrigation to the tree root zone is critical. We can conserve water by converting turf to xeriscape AND protect our valuable shade trees.