National Trust for Scotland said it had found growing numbers of coins embedded into trees at its properties.
"We wish you wouldn't do it, especially to live trees as it harmful."
NTS urged people to donate their coins to the conservation charity instead.
One of the most celebrated trees could be found on Isle Maree on Loch Maree, where pilgrims travelled to attach their offerings.
In the late 19th Century, the tree was covered in hundreds of nails and 'countless pennies and half pennies'.
One account of the tree said: "The effect is that the tree for about eight or nine feet up from the ground is covered with metallic scales.
"The scaly covering forms armour something like what is depicted on a dragon.
"Visitors go there to see the tree and hammer in coins and probably wish a silent wish before leaving."
The tree, which was also visited by Queen Victoria, later died due to the damage to the bark.
It us understood that the tree suffers copper poisoning after coins are pushed through its surface.
The warning from National Trust for Scotland about the trees prompted a reaction on the charity's social media channels.
One woman said: "Why? I don't understand this whimsical vandalism. It is the same with love locks. What is the point? Why litter beautiful natural places with such things?"
Another added: "Wish people would just leave a place the way they found it, this kind of crap is just permanent litter."
One user said: "Too much of this going on. Rock stacking, love locks, tying offerings to branches, and now this."