They'd love some bone meal mixed in with the soil, along with a handful or two of manure. I don't know if Chickity Doo Doo (don't blame me for the name!) is available but it's lightweight, easy to use, and it's all I use since the heavy bag of manure is just too difficult to handle for me now. Mulch it very heavily so the soil will retain the moisture. Four inches is not too much!
