You can expand your hydrangea garden by propagating or splitting your shrubs as they grow. You can propagate the shrubs using an existing plant. To propagate the hydrangea, choose a branch that is close to an open area in your garden. Strip the bark from the branch in a 1-inch wide strip all around the branch. The stripped section should be 6 to 12 inches from the end of the branch. Bury the exposed part of the branch in the soil and allow the end of the branch to extend out of the soil. A new shrub will grow from this buried branch. This method works best for Bigleaf hydrangeas.
You can also split your hydrangeas by digging part of the large plant out of the ground and replanting it in the garden. You can split moderately sized plant in half or split very large shrubs in quarters. Use a sharp knife or shovel to cut the shrub through the root area. Follow the original planting instructions when you replant your splits.
As your hydrangea grows, you can prune the shrub to control their size. Many hydrangeas grow on old wood, so pruning immediately after they finish blooming in the summer will help the hydrangeas develop old wood between early fall and the next spring. Take care as you prune your hydrangeas that you remove less than half of each branch. If you prune the hydrangeas too much, you might damage the plant and inhibit their ability to bloom the following summer.
Image courtesy of USDA.gov