I need advice on how to care for my big leaf hydrangea that has not shown any signs of growth since I got received her two weeks ago from a nursery out of state. Below is a photo of the plant in question. I have been watering them every day including the other three hydrangea plants that came with this. They are all doing well. They get morning sun and partial shade throughout the day. Thank you!
It appears to be a fungal infection. This is caused, mostly, by overwatering, or the plants roots remaining saturated for too long. This will deprive the roots, and beneficial microbes of oxygen, which will lead to pathogenic infection of "bad" microbes.
If it isn't too far gone, then you can attempt to correct this with dolomitic lime and wettable sulfur. This will kill off any infection, and restore the soil to a more suitable pH after.
Make sure, in the future, that you only water when the top two inches of soil are almost completely dry. During wetter seasons, it may not need water but every 2 weeks or so, where as if it is really hot, and dry, it may need it once a day, or once every two days. This will depend on how long it takes to soil to dry out quite a bit.