Like most flowering deciduous shrubs, a weigela (Weigela florida) benefits from regular pruning, which can stimulate strong new growth and keep lots of flowers coming year after year. It's also possible to rejuvenate an older, overgrown weigela plant by cutting it back heavily. Pruning isn't difficult, provided you do it at the right time of year, generally in early summer after major flowering has ended.
Choosing a Pruning Time
Weigela shrubs come in a few different varieties, most growing in U.S. Department of Agriculture plant hardiness zones 4 through 8. Their flowers are usually rosy pink, with masses of blooms appearing in spring and a second, lesser number of flowers again in summer. Most shrubs grow 6 to 10 feet tall and spread to become 9 to 12 feet wide, although a few are more compact. A cultivar called 'Red Prince' (_Weigela florida '_Red Prince') is an example that's only about 5 or 6 feet tall and wide; its flowers are deep red and it grows in USDA zones 4 through 8.
A weigela shrub has a two-phase blooming period; it blooms on the previous season's growth -- called old wood -- in spring, and again on new growth -- or new wood -- in summer. Major pruning is best done in mid-summer, after the shrub's finished its bloom season. With this schedule, it's possible that you might see a few flowers later in the season from buds that appear on new growth. You can also prune in spring by trimming back old wood, but if you do this extensively, you'll see few if any flowers until a few appear on new growth in summer. Avoid pruning a weigela in the fall because fresh cuts might not heal before the plant enters winter dormancy, and these could provide easy entry for pests the following spring.
It's important to make clean cuts without ragged edges when pruning, and to avoid tearing a weigela's bark. To accomplish this, always use sharp pruning shears or, for larger branches, loppers or a recently sharpened pruning saw. When pruning, wipe your cutting blade well with rubbing alcohol after each cut, to prevent spreading plant diseases.
For general pruning to keep the shrub's shape compact and bushy, prune flowering branches back to a point just ahead of the next side branch, also called a lateral branch. If you see branches that are crowded or rub on each other, prune these back; this also allows more light to reach the shrub's interior, which promotes heavy flowering. If the plant is mature and full-sized, you can also remove a few large branches at their origins to stimulate healthy new growth from the plant's base.
If you see some branches that are partially or completely dead in spring, when the plant starts growing after being dormant, these are likely the result of winter cold and severe weather -- called winter die-back. It's best to trim these dead parts off the plant to stimulate new growth. Make cuts just behind the dead portion, into living wood. Find this by scratching through bark with a fingernail; living wood is whitish-green under the bark while dead wood is brown and brittle.
Always make slanted pruning cuts, never cutting straight across a branch. A slanted cut allows water to drain away from the cut surface, helping prevent rotting and entry of disease organisms before the cut can heal.
If you have a large, older weigela that's become leggy, has slowed flowering and has been unpruned for several years, it's not too late to rejuvenate it and spur healthy new growth. Although you can cut the entire shrub down to the desired size, cutting it as short as about 2 feet tall, it's best to thin the plant out in an orderly way. Use loppers and hand pruners to cut back about one-third of the plant's oldest branches, trimming them back at their origins from plant's main trunk. For the remaining two-thirds of the branches, cut these back to bring the overall plant to the desired size.