How to take advantage of a black south facing wall

I have a fenced off garden that butts against the south side of my home that I would like to take advantage of. I'm in zone 5b in Atlantic Canada and the wall is nearly black which will store a lot of heat. There is no topsoil in this location, just subsoil with a 3 ft border of gravel 1 to 2 feet deep (foundation gravel pad) underneath of which is landscape fabric. My home is on screw piles so I'm not concerned with roots damaging the foundation but I shouldn't dig too big a hole and disturb their stability.

I've been going back and forth with various ideas and would love to hear some of yours.

I live in a cold climate too, much drier and further south than you, but much higher, so our winters are good and cold. I designed the house to be solar heated by a greenhouse I attach only for the winter. That's not going to work in Atlantic Canada, I guess, but anyway, here's my garden. The space with the greenhouse is open for 5-6 months of summer. I grow things that would never survive outside, like rosemary.

Good Morning Rebecca:  Would you mind detailing a little bit about the removable greenhouse.  We have thought for a while about doing something like that on our south facing walls here in Maine.  When its temporary that means it may be a bit flimsy and we have some snow (coastal) but we do have lots of wind.  Previously in another location we had 3 greenhouses, 1 plastic, 1 glass and 1 twin wall.  Difficult to see how any of these would work.  Thanks.

Ed Waters wrote:Good Morning Rebecca:  Would you mind detailing a little bit about the removable greenhouse.  We have thought for a while about doing something like that on our south facing walls here in Maine.  When its temporary that means it may be a bit flimsy and we have some snow (coastal) but we do have lots of wind.  Previously in another location we had 3 greenhouses, 1 plastic, 1 glass and 1 twin wall.  Difficult to see how any of these would work.  Thanks.

I dunno, my location can get insanely windy but it seems to hold. The current plastic has served three previous winters and still seems good. It's UV-resistant film; not as clear as I might like, but it does hold up well. The iron frame has these aluminum gutters bolted to it, and you use a zig-zag shaped long wire called a clip to hold the plastic in place. I bury the bottom edge of the plastic in a trench to hold it tight.