Q.Slow thin growth and curling leaves on our linden tree
We have several beautiful linden trees behind us. One of them (the smallest of them) seemed very thin this spring after an exceptionally cold winter. The branches are supple, but many of the leaves on the branches are curled up and dry on the edges. The trunk on this one tree is heavier on the bottom and tapers off, unlike the others. I don’t see any signs of insects. The trunks on all, but more so on this one have some gray/ greenish patches on them. Any ideas?

Certified GKH Gardening Expert
This does seem like a fungal infection. The most common cause is soil that remains wet for too long without a period to dry out between watering.
The course of action from here will be a fungicide. This article will help:https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
I would also apply DOLOMITIC LIME and WETTABLE SULFUR to the soil. Continue to do this once or twice per year, especially if you know that it may be a wet year.
This article will help you to grow Linden trees: https://www.gardeningknowhow.com/ornamental/trees/linden/linden-tree-information.htm