Old hydrangeas can be renewed by cutting the old wood back to encourage new branches. It is easier on the plant if you do this by thirds. The first year cut one third of the branches to the ground, the second year remove another third and the third year the final third. The oldest branches are the woody ones that look thick and brown. Do this in early spring or winter. No need to fertilize until late spring. A slow release plant food like Osmocote will help the hydrangeas recover from the shock. You can also cut the entire shrub to the ground and wait for new shoots to emerge and renew the shrub. This may take a few years before the new branches will flower again. Hydrangeas love moist, organic soil so a mulch of compost around the roots but not next to the trunk will help to renew the plants. If you do decide to replace the old shrubs switch them out for the much more productive Endless Summer hydrangeas. These new hydrangeas flower on old and new wood for an abundance of flowers. Keep growing, Marianne Binetti