Once you have uncovered the stones, you will need to cover the area with organic compost, lime and gypsum due to the soil being 'sour'. When adding lime to your soil, remember that using too much could change your future planted hydrangeas pink. Make sure you use just enough to 'sweeten' the soil. The instructions on the back of the lime packet will advise you on quantity. For good results, scratch Nitrophoska Blue fertilizer into the soil around your plants.