Ivory Silk tree + root girdling – how long will it take to recover?

(Question)

Hello,
I have a 7 year old Ivory Silk tree that was doing wonderful the first 3 years. The 4th year there was some yellowing of leaves in center of tree followed by early leaf drop. The 5th year the leafs were stunted in size and canopy was sparse but the tree had its blooms. I did at this point gently remove soil around base of tree and discovered some girdling roots. I removed the girdling roots and tried to expose more of the flare of the trunk. The 6th year the tree was about the same in regards to leaf size being stunted in size.
My question is….how long does it take for a Ivory Silk tree to show signs of recovery after girdling roots are removed and more of the trunk flare has been exposed. Is there anything else I could do to help this tree along or is it a lost cause at this point?

Thank you

(Answer)

It sounds like you want to do everything you can for your Syringa reticulata ‘Ivory Silk’ ( Japanese tree lilac)! It is not possible to accurately predict if or when the tree will fully recover, as it can take several years for roots to regenerate, and other factors may come into play.  Be patient, if the tree’s health does not seem to be declining, it may well recover.

When tree roots are severed, the balance between the crown (top) of the tree and its root system is altered, which  is stressful for the tree. For example, the roots you removed may have supplied some of the water and nutrients to the tree canopy, and the tree will need time to compensate for this loss.  As well, removing the girdling root created a wound, which could leave the tree more vulnerable to disease and pests.

I mentioned that other issues may affect a tree’s recovery time.  For example, the season the girdling roots are removed may have some impact; Johnson (see link below) notes that in a study involving red maple trees, root removal in the summer resulted in better growth over a 2-year period than when the roots were removed during the fall or summer/fall combination.  Although this study related to a different tree than yours, it illustrates that  there may be other factors that impact tree recovery, which we have not considered.

In any event, best practices to enhance recovery of the tree after removal of girdling roots include:

  • Water the tree deeply and well, over the entire root system, especially during dry periods over the summer.
  • A light surface mulch on the exposed roots helps retain soil moisture. Do not pile mulch on the trunk flare – it should not touch the trunk.
  • Prune any dead branches every couple of years.  Expect branch dieback, this is normal during the recovery process.
  • Consider whether the soil is deficient in nutrients, which could contribute to the stunted/yellowing leaves. If this is the case, slow-release nitrogen fertilizers may benefit the tree.  Caution – don’t overdo it — excessive fertilizer could result in too much above-ground growth, stressing the already weakened stem and root system.

Here are links to a couple of good resources:

Finally, you may want to consult an arborist to confirm that your tree is indeed on the road to recovery.  Landscape Ontario  provides lists of various experts, including arborists, in your area.