How much space must be left between two hives.
The ideal spot in my garden, next to a south facing wall lies between a greenhouse and my garage. It total this is about 2m wide.
What spacing should I leave between two hives ?
...
As others have said, the hives could be touching.
Not ideal, but possible.
It would be very helpful if the hive entrances could face in different directions, but another twist is to ensure that the hives are bee-identifiable as being recognisably different. Bees can recognise colour differences (but can't tell red from black) and *some* shape differences (principally between a solid shape and its outline version). So some *different* yellow, blue or green 'mystic' decoration of the entrances will help.
Its quite usual to have a pair of hives on a single stand about 1.5 metres long.
But mounting the hives at different heights would also help the bees distinguish the hives - though it may make beekeeping a touch more awkward with at least one hive not being at an ideal working height for you.
HOWEVER, with them being backed up against a wall and squashed in between garage and greenhouse, my concern would not be their proximity, but the bees flightpath -- and how that might interfere with people using the garage and greenhouse, and whether you recognise that this position is going to demand that you approach the hives from the front (which is "sub-optimal" - especially if/when the bees are being "defensive").
And also recognise that 1m workspace behind the hives is likely to be needed for you to work comfortably - possibly pushing the flightpath (or beeline) a metre closer to the garage and/or greenhouse entrance.
There may also be a question of the shade from the garage, but this is going to depend on the detail of the site layout. (Better shaded in the afternoon than in the morning!)