I recently purchased a Nikko Blue hydrangea. Some of the leaves had some brown on the edges. I cut them off, but I'm still getting the brown on the leaves. Could it be a disease or am I doing something wrong? Thank you.
This could be a number of things--too little or too much water, over fertilizing, leaf scorch (if planted in too much sun), etc. Typically, in hydrangea, this is caused by a watering issue. Has it recently been planted? If newly planted, there may be gaps in the soil around the root ball that is drying out the roots. I would tamp down the soil around the plant. I would also recommend upping the watering. In addition, it could be suffering from shock. This article will help with that: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm