Trivial problem

Why is he doing this if you have asked him not to?
Say it again, a bit more forcefully, they are your trees after all.

Why would you let anyone in your garden to decimate your shrubs? Does he live with you ?
None of my children would dream of walking into my house or garden and start doing something that hadn’t been asked
Where are your boundaries ?

Make a bargain with him: For every cut he makes, you are allowed one on something of his........T- shirt in half, mouse cable, page from a book.etc.
But honestly, just exert your authority! Your property not his!

He needs a right rollicking. Any offspring of mine that did something like that would certainly get one. I like stree's idea.

Good idea stree you really need to be firm on this one Alexa I don't think resorting to hiding the tools should be necessary. I have perfected ' the look ' which my children and grandchildren know means business.

Is he a tree surgeon - or a wood butcher as DH would call him?

Lemongrove, I have wondered why he does this. He also placed little mats at front and back door although I explained they are a hazard for my walking frame. This son is very sympathetic and affectionate and has been literally a life saver during my recent back injury. Everybody loves him.

It sounds like he's a very nice man and he thinks he's being helpful but it is rather insensitive and patronising to, in effect, dictate what happens in your own house and garden.

Tell him more firmly that you want him to leave the trees alone. And you are right, little mats at doors are not a good idea for people who have mobility issues (of for anyone really as it's easy to trip on them). Just put them away somewhere.

Has he got a woodburning stove?

Jalima

Thank him for "trimming" the trees, tell him you think they have been trimmed enough and would he please now start on the ivy

Your his mother ....remind him of his manners!!

put your foot down , if that was my son I would say jokingly f you persist in trimming my trees which I don't want I will be lopping off a certain part of your anatomy ,..., that should cure him ..

You need to lay down the law and have a strong word with him or ban him from visiting until he obeys your rules. Like a naughty child springs to mind.

morningdew

Is he an horticulturist? if not tell him to leave things alone.

Oh yes he is very nice as are most of our DSs but you're still his DM and he needs telling! Touch MY trees at your peril.

He sounds alarmingly like my partner, who does things like move the mat outside the back door several inches away from the door itself, so that you step out only half onto it and risk going flying. After 15 years in this house, I finally lost my rag the other day and tore the elastic band off the plug in the kitchen sink so that water actually stays in the sink instead of leaching away all the time. He was so shocked at my finally taking a stand that he’s left it like that. I’m tempted now to try it out on a few more of the weird things he does. : )

My Mum's partner is a "nice" man whom everyone loves but he is like your son...it doesn't make it any more irritating. It is a form of passive aggression if you ask somebody not to do something and they continue to nicely do so. Be appreciative about his help by all means but be assertive about things that aren't helpful.

Find an internet page by an expert explaining how to trim your trees and send it to him.

No-one would touch my garden twice unless I gave specific instructions. DH even if I pointed out clumps of plants & said leave those alone they're not weeds would dig them up. He was banned from weeding except under my strict supervision

You do need to be firm with DS & tell him not to touch

DS weeded out all my carefully planted aster plants.
I tend to be an over-enthusiastic pruner.

Send him round to me. There is nothing in my garden that doesn't need a trim!

Alexa
I can't understand people who can't run their own lives. Do you just look on helplessly and go with the flow, even when he does stuff you object to? It sounds as if you're a doormat.
If you can't or won't assert yourself then nothing we say will change your son. Unbelievable.