Avoid planting it in hot, dry, exposed sites. Most people buy hydrangeas when they are blooming, but spring or fall is the best time to set them out. For planting, dig a large hole approximately two feet across and one foot deep. Bigleaf hydrangea responds to several light applications of fertilizer during the growing season. It is not necessary to remove the mulch when fertilizing, but water soon after application to help dissolve the fertilizer and send it into the soil.
Hydrangeas have such big leaves that they can suffer if set out during hot weather.
They need plenty of water, so plan to water thoroughly once per week or more frequently. Avoid pruning after August 1. One of the easiest ways to propagate bigleaf hydrangea is by layering. This is done by digging a trench near the plant and bending a section of limb down into the trench. Use a knife to remove a small ring of outer bark about an inch wide all the way around the limb.