Q: Is it possible that a two-year-old hydrangea has outgrown its nice comfy soil mixture and is being stunted by the clay around it?
A: That is indeed possible if a wide area of soil was not loosened around the shrub when planted. Hydrangea roots know a good thing when they see it, so they prefer growing in soft, organic soil. Within a couple of years the top of the plant will grow too large for the relatively small soil ball in which the plant originally grew. Your hydrangea won’t be able to get the moisture and nutrients it needs. Before planting, always loosen an area five times as wide as the plant rootball and consider mixing soil conditioner with the native soil.