i would look at the manufacters website they should have ph values as well as a plethora of other info. dont breathe that dust though you could end up in a hospital with some coal miners. my main concern is with your compost as it tends to be very rich(not good especially for young stock) thus you may want to dillute that down to one part with a light soil mix. that would depend a lot on the quality of the compost and soil you mix with. if they are young dont use it at all.