Big blue hydrangeas are showy shrubs that provide colorful blooms throughout the summer. Gardeners must prune hydrangeas carefully so they do not disrupt future blossoms, because big blue hydrangeas bloom on the growth from the previous year. Prune in the summer after the blooms fade so you do not damage the terminal buds of the hydrangea shoots. The terminal buds are the buds at the tips of the stems.
Watch the big blue hydrangeas as they bloom in the summer. You must prune these hydrangeas immediately after the blooms fade on the shrub to enable the plant to produce as many blooms as possible in the next growing season.
Use the pruning shears to cut off the bloom. Cut the stem off at the point on the stem below the bloom where you see the strongest buds. This will be the point where new flower shoots will grow from the stem.
Examine the plant and prune away any weak, dead or damaged stems. Cut these stems off at the soil level. As the plant grows larger, each year you must remove old stems and any stems that rub on each other. The point where stems rub on each other can be a point where infection enters the plant.
Leave stems alone that have not bloomed during the current summer.These stems might yet produce blooms, and if you cut them off you will remove future blooms.
Prune overgrown hydrangeas more drastically, if necessary. A hydrangea that has not had regular pruning for several years will appear misshapen and leggy. If this is the case with your hydrangea, cut each stem back to the strongest buds. This pruning method could eliminate future blooms for the next season, but it will produce a healthier and more vibrant hydrangea that will bloom with more vigor in subsequent seasons.