Along my front porch, which is in partial shade most the time, I have some hosta, iris, lamb's ear, silver dollar, lily of the valley, and day lily... all doing fair. Before I put these plants in three years ago (when I bought the house) there were arborvitae growing in this location.
The soil is hard and gray. What should I add to it to improve it -- compost? manure? humus?
The first thing you need to do is get a soil test; contact your local extension office for the information the test kits are very reasonable.
After you get the results back you can then acertain what ammendents you will need.
Please feel free to Email me if you have any ?
Put in raised beds and just use your own soil mix. That way you can flowers ASAP instead of waiting for years for your soil to get in good condition. The raised beds will also prevent roots etc from disturbing your foundation.
A good mix would be 1 part compost, 1 part top soil, 1 part peat moss, may a bit of sand in their too.
If you don't want to gfo the raised bed route add all of the things you mentioned and also add time as it will take several years for the amendments to work. Oh and keep adding compost etc., at least twice a year.