Neighbour put flower bed against my wall, potential problem?

Hi, I’ve finished building a property where the garage is on the boundary with the neighbour. I have perimeter concrete right round the house but not next to the garage as I can’t obviously pave the neighbour’s land. He has now built a flower bed against my garage wall. Put a 2 brick high enclosure for it and filled it with soil. These Bricks don’t touch my house. It isn’t past my damp barrier but is close as in 5cm maybe. The brick wall is about 20cm above what was the ground level. He cut away the loose orange plastic membrane that was coming out of the ground next to my slab.

Should I have any concerns about moisture affecting my slab from this new flower bed?

How about termites?

Wanting to see if I am worrying over nothing or if I need to try and come to an arrangement with him?

You will surely face some problem.

what specifically?

Probably water damage water getting onto the wall might make efflorescence, might also attract bugs like booklice (psocids) and termites.

It is just a garage. I'd go and ask if you can paint waterproofing on the slab edge. It's your property so you are entitled to waterproof it but you obviously need to access his property to do it.
That will help prevent moisture problems just in case they end up put soil in there.

Excellent suggestion chippy.

Nothings gonna happen.
Exposed slab edge will always come in contact with soil or moisture at ground floor. If your that precious do what chippy said and ask them if you can apply the WPM to the edge.

Depending on you soil profile, clays will absorb the extra moisture causing localised heave which will cause cracking to you concrete floor minor movement to the cornice and hairline <1mm cracking to bricks, Do a search for CSIRO BTF 18 "Foundation Maintenance and Footing Performance: A Homeowner's Guide", it will explain the risk, a garden generally gets watered "A LOT".

You’re in WA so you will be fine. Water drains away easily and is nice and stable.

Is your situation the same as above?
Ultimately it's not a good idea to stack soil up against brick walls.
Sand drains well and doesn't have issues with movement due to moisture like clay soils but if it's a double brick wall it introduces areas where termites can move into a cavity without being seen or if it's a single brick wall the damp soil will allow moisture to wick through the brick to the internal side.
The OP only had a very low level retaining that the neighbour had built that only got to the footing height. In WA typically the footing is lower and you will see brick. In that case I'd waterproof the bricks right down to the footing to the height of the proposed soil height.

Typically the footing is one course below the ground level outside.
The general way construction works in WA is the slab is 2 courses above the footing and then there is a one course (86mm) step down out of the house onto ground level.
This can vary slightly if there have been dropped footings put in but most houses on flat blocks work as I have mentioned.

If you explain what you were trying to do I can give you a better idea of how to approach it.

So are you planning on building garden beds against your house or are you concerned about a zero lot wall on the boundary?

They can't use the side of your house as a garden bed. The OP's neighbour had only put very low almost garden edging in that wasn't going to pile dirt against their brickwork.
If your neighbour plans on building a raised garden bed using your zero lot wall as a back edge you will have to have a chat with them. The wall isn't designed as a retaining wall it's designed to take compressive (downward pressure) and not lateral pressure from having soil pushing against it.

The wall isn't theirs, it belongs to you and is on your property
They can't put soil up against it, they can't attach items to it.
The OP's question related to a really low and minimal little garden border that really wasn't going to have any impact.
If your neighbour wants to build a garden bed they need to put a back on their property that retains the soil from resting against your wall.
I'd have a polite chat to them and let them know that they can't just pile soil up against your house.
If it was just a really low garden edge (maybe only a couple of courses) then you could probably let it slide and just waterproof the wall from the footing up to the height of the proposed soil. If it's any higher than a couple of courses I'd be asking them to put a back on their garden bed.

All this is based on having no actual idea of what your neighbour is proposing or has already done.
In my experience you don't make a big deal about small things with your neighbours because there is nothing worse than having beef with someone you see often and may possibly need at some point.
Reasonableness is the key. From what you have said I kind of have visions of a 500mm high garden bed built against your garage and in this case I would definitely say something. The moisture will come through the wall and will have a detrimental affect on your property.
Even attaching things to the wall isn't the end of the world but I'd expect them to talk to you first and explain what they intend to do and how. I've seen to many home handy men drill right through single brick walls and blow the bricks out. Again it will be your problem because it's your wall.

So is it your garage or is it your neighbours?
I'm kinda getting the sense that maybe it's the neighbours garage and you would like to build up against it and attach to it.
Zero lot walls belong to the person whose property they are on. The neighbour isn't permitted to use that wall as their own either to build against or attach to.

All good then.
All the best with your build.