Renew and control size
Thin shrubs by cutting branches back to a main branch or stem or by removing the oldest stems on mature shrubs by cutting them back to the ground. The latter encourages strong new stems and flowering. Thinning also helps control shrub height and width and decreases the need for severe pruning.

Many deciduous flowering shrubs, including viburnum, forsythia and beautyberry, respond well when one-quarter to one-third of the oldest stems are removed each year. Doing so completely renews the shrub every three to four years.

Shape
After thinning, occasional wayward or overgrown stems may need trimming back, called heading, to enhance the natural shape of the shrub.

Because heading cuts promote branching, it's important to use them prudently. Otherwise, dense growth will develop at the ends of branches and will shade out the rest of the plant, resulting in sparse foliage on the inside. For the same reason, don't head back all the branches to the same length or shear flowering shrubs into globes and boxes. This not only makes them look stemmy, stiff and awkward, but also prevents them from flowering.

Rejuvenate an old shrub
Certain shrubs, even though badly overgrown, can be restored to new vigor by cutting all of the branches back to 4 to 8 in. above ground level. The best time to do this is during the dormant season before new growth starts. The plant will be entering its most vigorous growth period so it will be most resilient.

By summer it will renew itself with healthy, vigorous growth, and within two to three years the shrub will totally fill out. There are a couple of drawbacks to this approach, however. It is usually necessary to thin the regrowth, and flowering could be delayed by as many as three years for some shrubs.

Cut back only those shrubs known to respond well, such as forsythia, honeysuckle and butterfly bush. If in doubt about a particular shrub, consult the local extension service or a good reference book.

Pruning takes courage. But flowering shrubs are forgiving, and they want to grow. As long as you know what you're trying to accomplish with each cut and when you should make the cuts, you can't go wrong.

Prune in winter or early spring

Prune just before flowers fade
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