Sick Oak Tree and Its Spring Recovery

Q. I have a sick oak tree in our backyard. It is an older tree and but not growing well. Our gardener suggested hiring an arborist to treat the tree and help it recover. Can we purchase something to correct this? Would an arborist be able to save it? Your thoughts.

Sick Oak tree trunk in the backyard. 'Heritage' live oak is a good tree choice for two-story homes in Las Vegas.

A. From the picture you sent it looks like a southern live oak such as 'Heritage'. It looks like the trunk of the tree is slow to recover and has some pretty old wounds. Getting it to recover depends on how far “gone” it is. You will not know that until the summer hits. Even though it's a 30 to 40 foot tree (size-wise think of it as a bit larger than European olive). This particular oak is classified in between xeric and mesic and a native to southern Texas and into the Chihuahuan desert. It does well where there is a bit more water and also into the drier locations. The "cons" of this tree

       All oaks like amended soil and don’t like the soil “mineralized” by rock mulch over time. Rake the rock back three feet from the trunk. Change this area over to a layer of organics that can rot on top of the soil. Add a thin layer of finely screened compost to the soil. Water the tree two feet deep once a week right now. This can be done with a sprinkler on the end of a hose. This may be increased to twice a week if it gets hot and windy.

            Oaks in general dont like rock up to the trunk but prefer growing in soils getting organics periodically. Rocks cause the soil to become “mineralized” over time (organics in the soil are lost to decomposition). This is the reason for adding compost and wood chips to the top of the soil.

Tree roots require deeper irrigation. The bigger the plant, the deeper the roots. Use a length of rebar to judge how to deep to water. To get water deeper with the same amount of time, add more drip emitters!

            Secondly, this tree needs additional water each time its irrigated; 15 to 20 gallons during the first few years but now may be 30 to 40 gallons each time. Instead of increasing or decreasing the minutes, add more and larger drip emitters to the area under the tree. Put sprinkler hose water into a 6 to 8 foot wide area under the tree for about one hour and encourage the roots to “chase” the water into this newly wetted area. This will increase the trees vigor and cause it to heal fast. No need for additional fertilizer if the compost is rich with nutrients.

            If you see evidence of borer activity from previous years, it probably was reinfested each year since that time. Soil drench the area under the tree with a borer systemic insecticide. Apply it as a soil drench after the tree finishes flowering.