Hydrangea Petiolaris will need support at first but will use pads to cling to the wall later. Might be a good idea to make a large planting hole and remove half the the clay and replace it with a peat or general purpose compost. Use bone meal to give the roots a good start and to keep feeding it over the winter. Make sure your wall is in good condition if you choose something like ivy.It will not damage a wall in good condition but it will put roots in to any crevice with not so good results. I believe pears can be grown as an espalier on a north facing wall. Welcome to Goy