Q: My Linden has small leaves on most of the tree except the part over the deck. The tips of the branches are dying back, and the leaves are turning yellow between the veins. Our yard was landscaped five years ago, and I irrigate and fertilize my lawn regularly, and the tree is in the middle of the yard.
A: The size of the leaves means the tree did not have enough energy to produce full-sized leaves. This tree is under a considerable amount of stress, indicated by the dying tips. Dying tips usually indicate a problem with the roots.
Because the tree was planted five years ago, transplant shock or damage to the roots during planting can be ruled out. The tree should have become established by now as long as it was not very large (greater than 4 inches diameter) when planted.
The yellowing leaves indicate a nutrient deficiency, usually iron, but magnesium also could be deficient. One might assume the soil lacks enough nutrients, but Lindens rarely have that kind of a problem in this region. Because you also fertilize and irrigate, we can rule out that as a problem too.
One possible cause is weed-
wacker or lawn-mower damage to the trunk of the tree. Damage to the cambium, the living layer of the tree, can cause severe stress. The cambium is just beneath the bark, and when the top layer is damaged or ripped off the tree, the cambium underneath will die.
The portion of dead cambium can no longer function in its role to help transport water, nutrients, hormones and other compounds.
Roots usually serve different sections of the canopy, and it appears the roots under the deck are not affected by whatever is happening. That would lead to a problem with the roots within the lawn area.
Lindens are sensitive to a chemical used in most “weed and feed” fertilizers, called dicamba. It could be possible that the chemical is killing roots, resulting in small leaves. This also is likely the cause of the tips of branches dying.
Nonfunctioning roots cannot absorb the proper amounts of nutrients, and this is causing the yellowing between the veins of the leaves.
Because the chemical dose is not high enough, the tree has been stressed but did not die. However, dicamba accumulates in the soil and will eventually kill the tree.
I suggest you apply organic fertilizer to your lawn to restore the natural balance of nutrients and organic matter to your soil.
Earthworms and micro-organisms important for root development and growth also will appreciate this change. Use a spot spray to control weeds. Mow lawn to no lower than 3 1/2 inches high. The extra shade will help keep soil cooler and shade out germinating weed seeds.
Remember, in nature there is seldom an easy chemical fix. Products that promise great rewards for little work often come with a hitch. “Weed and feed” fertilizers and “three-month insect control” products for lawns can damage the ecosystem. Use them with caution and an understanding of what is happening. Plants have evolved over eons with many thousands of micro-organisms within the soil. There are many symbiotic relationships that benefit tree roots within the soil.
Robert Brudenell is a registered consulting arborist and owner of The Natural Way Inc. Send questions to Robert@thenaturalwayinc.net.
