I had an email from a nice lady called Heather yesterday: *waves* which made me roll my eyes in sympathy.
Heather has a beautiful beech hedge, and her neighbour's brambles throw themselves over the boundary and infiltrate this hedge, so when the hedge is trimmed, the brambles - not unreasonably - get chopped.
Apparently the neighbour came round and complained about the loss of blackberries!!!
So what can you do in this sort of situation?
The first rule is "Don't fall out with neighbours if you can possibly avoid it" which usually means talking to them. It's always tricky when inter-neighbour communication starts with a complaint, but it's worth gritting your teeth and accepting that part of being a grown-up is having to do things you don't really like doing, and sometimes an apology (no matter how insincere) can prevent years of low-level war and bad feeling.
If "one" had known beforehand that the neighbour was going to complain, "one" could have been ready to say "Oh, I'm terribly sorry, I had no idea
that they were of value to you, I thought that they were just wild
brambles which are making a terrible mess of my lovely hedge. Can I
suggest that if you don't want them chopped, that's no problem, just
keep them on your side of the boundary." and I would suggest that in most cases, it's worth going round to their door and attempting to say something similar.
But before doing so, take a look at the boundary and see what you can do to make life easier for both parties: what sort of fencing exists? Can it be mended, strengthened, replaced? Is there a way for you to repel the brambles before they get to your hedge?
I've written about brambles several times: if you go to the very top left-hand corner of this page you will find an orange "B", then an empty box with what looks like a Q in it: I'm not sure if that is meant to be a magnifying glass symbolising "look closely" or is simply a Q for Question, but either way, it's a search box, so type "brambles" into it, to get a list of everything I have ever written on the subject.
If you don't have time to do this, skip to this How To Deal With Brambles article, which explained how brambles grow, and why you don't need to dig our yards of roots, but you DO need to get a couple of inches below soil level.
Then check out Bramble Removing: Invaders From Next Door, which has a few suggestions on ways to deal with this annoying issue, and some additional information in the article prompted by the question What Shrubs Can Hold Brambles Back? (answer: none, but there are some more comments and suggestions about fencing and tactics).
In Heather's case, she mentions a fence which is presumably "behind" (from her perspective) the hedge, and this makes it a lot easier to solve the problem.
If there is a fence of some sort, then the answers are in the articles mentioned: basically you have to patrol the boundary once a fortnight or so and fold back all invading stems, pushing them firmly back over to "their" side. Don't cut them off, or you will double your trouble - just fold them back, flip them over the fence until they catch on themselves and stay back. Any stems that are forcing themselves through the fence must be pushed back through the slats.
If the fence is decrepit and full of holes, then whoever owns it should be advised to replace it. In Heather's case, if the fence is hers then she has the option to install a stouter fence, possibly higher than the existing one, which will help to keep the brambles out of her hedge. If it belongs to the neighbour, then the neighbour could be politely advised that if they want to get the best crop from their brambles, they should replace the fence, and put wires along their side of it, to train the brambles properly.
You will need to get behind your own hedge in order to do this, but this is not a bad thing: it might mean that you have to clip the "back" side of your hedge instead of just letting it grow (bashing up against a fence usually restricts the growth of a hedge in a sort of "natural pruning" way), but this will make it easier to keep the base of the hedge clear of weeds and other undesirables, and might well make it easier for whoever trims your hedge, if they can access it from both side. And it helps for boundary maintenance, too.
So, in short, the advice is to trim the back of your hedge so that you can get behind it, then make a point of tucking or flipping back all new bramble growth as soon as it gets over to your side. This should please the neighbour, who will see more stems and therefore more crop - and it will keep the darned things out of your hedge. Once the hedge is clipped, it should only take you five minutes or so every couple of weeks, and peace will be restore: and who knows, if you get on good terms with the neighbour, there might be a pot of bramble jelly for you, later in the year!