Keeping flowering shrubs healthy, vigorous, and blooming profusely can be tricky but manageable. The most important part is to determine whether they bloom on old or new growth.
Plants in this group fall into one of three important categories:
Early-blooming shrubs that flower in spring.
Late-blooming shrubs that flower in summer.
Remontant or “everblooming” shrubs that bloom in spring and summer.
Pruning common shrubs like lilacs, forsythia, and burning bush into tight mounds is not only unnecessary but isn’t that great for the plants, either. Many flowering shrubs will look their best when allowed to grow in their natural form or habit.
Spring-flowering shrubs bloom on branches formed the year before such as azaleas, lilacs, forsythia, and fothergilla. Don’t prune in the early spring or you’ll cut off this year’s flowers. Wait until right after the flowers are spent because these shrubs need time to form the buds on new summer growth for next year’s flowers. If you cut too late, you’ll cut off those buds and miss out on the blooms for a year. Most of these plants don’t need heavy pruning every year, just some selective thinning of branches to give them a nice shape.
Summer flowering shrubs include most, blue mist spirea, Hancock coralberry, mockorange, potentilla, Spirea bumalda and S. japonica, Annabelle and Pee Gee hydrangea, shrub-althea (Rose of Sharon), snowberry, and St. Johnswort. Removing older canes of flowering shrubs also allows better sunlight penetration into the shrub. This results in better flowering throughout the shrub, instead of flowers just at the top where sunlight is sufficient. On shrubs noted for their bark color (like Red-Twig Dogwood), the new shoot growth has a more brilliant color. Routine pruning at the base encourages new shoots, which have the desired red color
Everblooming shrubs, particularly hydrangeas, bloom on old wood in spring and produce summer flowers on new wood in the same growing season. For these remontant types, limit your pruning to minimal shaping to keep old and new wood intact for blooms
Some bushes such as Butterfly Bushes do not need to be pruned every year.
In fact, you only need to prune them when they get too large for the space allotted. But since butterfly bushes only bloom on new growth, many gardeners prune them severely each spring to encourage lots of new growth and lots of flowers.
You are safe to prune it in the spring. Avoid pruning in the fall and winter. The reason being the stems are hollow and any water that accumulates in the stem and subsequently freezes will cause the wood to split. That’s not a good thing. Butterfly bush bloom on new wood so as long as you have plenty of sunlight, you’ll get lots of blooms throughout the summer by pruning in the spring.
Cut back all of the woody stalks by about two-thirds in early spring and remove any weak shoots sprouting from the ground. This hard pruning encourages stronger growth at the base of the plant, producing new shoots with flowers developing at their tips throughout the summer.
In the fall, prune away all of the tips to remove any faded flowers and developing seeds. In some areas, buddleia has become an invasive pest. Deadheading and removing the spent flowers before they go to seed is an important step in reducing the chances of butterfly bushes escaping from the garden and into the surrounding fields and woodlands.
It takes some time for your butterfly bush to flourish each year, so give them adequate time to bounce back in the spring.
A fertilizer application in March or April and again in June or July will help to encourage growth. A generous helping of compost or all-purpose organic fertilizer is recommended. If you’re inclined to use synthetic products, a tablespoon of 10-10-10 for each foot of height is appropriate. Sprinkle it around the shrub out to the drip line, but no more.
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