Welcome to gardening and glad you love hydrangeas as I do too. The problem is hydrangeas like cool soil and lots of water. The plastic weed block and rubber mulch heats up and blocks water and your hydrangeas may not do well. I suggest you wait until spring and then if the hydrangeas fail to flower remove the plastic weed block by cutting it away all around the root zone or about a 3 foot circle around the hydrangea. Replace the plastic mulch with wood chips or bark dust or better yet some bagged compost. Then in spring you can add the Osmocote around the base of the hydrangeas as the once a year feeding. Keeping the roots cool and moist, and shade from the hot afternoon sun will grow the happiest hydrangeas. Keep growing, Marianne Binetti