linden tree problems

Asked October 3, 2019, 3:03 PM EDT

We have a linden tree in our front yard that is looking fairly sickly. Its leaves are small, sparse, and curled.
We had an arborist come out early last spring, because at that time the leaves were sparse and yellow.
He injected iron and nutrients into the ground around the tree, and now the leaves are not as yellow, but it still doesn't look right, and we don't want to lose it. Its really a nice tree.
Do you have any suggestions of what we should do?
Thank you.

Mark Sandvick, Loveland

Larimer County Colorado

1 Response

Hi, Mark. Without photos, it may be hard to say, but it is coming to the end of the growing season, so this could be natural yellowing. I live in Loveland also, and have noticed several linden trees suffering from leaf scorch, and yellowing as well, here in town, and down in Longmont as well. Lindens are susceptible to leaf scorch. But yes, I think it very well can be due to the fact that we had some hot temperatures in September. Take a thin bladed screw driver, about 10" long, and insert it into the soil under the tree at the drip line, to see if it goes in easily. If you can push the screwdriver into the soil easily but not too easily (ie, if it goes into the soil up to the handle), then the tree is probably getting enough water, but if you meet resistance, the tree may need to be watered more. Keep in mind that fairly mature trees require 10 gallons of water per 1-inch diameter of the trunk, (measure trunk diameter at 6" above ground level) per month, even in fall and winter. In the fall and winter, trees with shallow root systems, such as lindens, require supplemental watering during dry periods, when we have had no measurable rain or snow for three weeks , in fall and winter. Also keep in mind that, if you are using a deep-root watering tool, but inserting it too deeply, you are probably going too deeply to benefit the roots. Lindens are shallow rooted trees.Trees obtain water best when it is allowed to soak into the soil slowly to a depth of 12 inches. Methods of watering trees include: sprinklers, deep-root fork or needle, soaker hose or soft spray wand. Apply water to many locations under the dripline and beyond if possible. If using a deep-root fork or needle, insert no deeper than 8 inches into the soil. As a general survival rule, apply 10 gallons of water for each diameter inch of the tree. For example, a two-inch diameter tree needs 20 gallons per watering. Use a ruler to measure your tree’s diameter at 6″ above ground level.
It could also be aphids causing your linden tree's leaves to curl. Check the leaves to see if they are sticky. Aphid "poo" is sticky because they feed on the juices in the leaves. You might also see wasps and other insects flying around, attracted to the aphid "honeydew". With colder weather coming on, the aphids should get zapped, but they will lay eggs in protected crevices on the tree, and around buds, and the eggs hatch in the spring, so you would have linden aphids again next year, if not treated.

As to the iron that your arborist gave the tree, you are correct in thinking that lindens are susceptible to iron chlorosis, so you are doing well to monitor for that and treat as needed. Plants affected by iron chlorosis first show an interveinal chlorosis, where leaf veins remain green and the rest of the leaf tissue turns pale green or yellow. New growth will show symptoms of chlorosis first. When it is needed, one treatment per year with chelated iron should do fine. Again, try to determine if an environmental factor or cultural factor might be causing the chlorosis: that is water saturation or oxygen starvation (if the soil is water-logged, or if the tree is planted too deeply) or drought, and alleviate those factors, if they can be corrected, first.
If you would like to take a photo of the tree, the leaves in question, and possibly the trunk of the tree showing how it is planted, we could look and try to determine better.
You could also contact the Larimer County Extension office (970-498-6000) between the hours of 10 am and 1 pm, on Monday, Wednesday or Friday. There are master gardeners on duty during those hours. You can request an onsite visit from the tree team to look at your linden tree. There is a charge of $25 per hour, with most visits completed within an hour.