Why does my hydrangea get black spost on the leaves? I sprayed it

The concrete has to be super clean and if there has ever been any kind of spill that had a petroleum base, super clean is critical. There are cleaners specifically designed to clean concrete. If you paint it (garage floor paint) and its not clean, the paint will bubble up then chip off over time. I would stain it. Home Depot or Lowes can walk you through the process.

Call a garden store/nursery, or call your state university's Extension Service. You can find them online.

caused by a fungus that spreads via spores in wet or humid conditions. To control leaf spot, avoid watering your hydrangeas from overhead, and again, remove and destroy diseased plant parts.

Thanks ,I have been watering from the top. I will stop doing that.