Elanor, sorry I didn't get back to you sooner.* :?* You said, "Is it OK to include the coffee filters in the compost?"* Yes.* Some folks are purists and don't like using the white coffee filters because they are bleached.* If you use the tan or white ones it's still ok by me.* :)*
You asked, "I have avery shaded area close to the house that resists just about anything I plant, yet an isolated bunch of myrtle grows there, and a few sickly hosta. The soil there is very clayey-- how to amend an area with compost?* I don't make that much compost. Should I get some garden store manure?"
I would recommend you add 4" of compost and dig it in as deep as you can.* You can purchase compost in bags at just about any garden center. You don't need manure, compost will work just fine.* You could even add chopped leaves and coffee grounds in the fall and let it decompose over the winter.* Then you can plant.* If you are just adding the leaves they are considered 'browns'.* Add some coffee grounds to the mix as they are considered 'greens'.* Get a big bag from Starbucks (free to gardeners) and add that to the leaves.* It will help the leaves to break down faster.
You asked, "I'm also wondering why the begonias and the boxwoods are doing so well, but the azaleas and lamium died right nearby?"
Maybe you should have a soil test done for that area.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.