Multiplying the Blooms on Flowering Shrubs
It’s easy for home gardeners to double or triple the number of blooms on flowering shrubs like Lilac, Hydrangea, Spirea, and Weigela. All it takes is regular shearing once a year, particularly when the plant is young, along with regular feeding. There’s a technique to doing this, and a reason it works so well..
When woody plants are sheared or pruned, they will “fork” just below the cut. At least two but as many as five new branches will sprout along the stem, each one with a “growth tip” or bud at the end. Most woody shrubs bloom on their new growth, so the bud is a flower bud.
Young shrubs typically have only a few branches coming from the base of the plant, and these branches tend to get long and gangly if they’re not trimmed. Often the weight of blooms will then cause these sucker branches to sag. Trimming young shrubs each year will encourage better branching habits and a more mounding shape, as well as stronger branches that won’t droop.
Good nurseries regularly shear young shrubs several times during production. They call this “cutting to the can” or “shearing back to a flush” because the first thing the plant does after shearing is “flush” or sprout a bunch of healthy new shoots. Nurseries time this flush to the selling season, because freshly flushing shrubs look nice and fluffy and start to produce flower buds, making them easier to sell.
Once the shrub is in your yard you should continue this practice each year until the plant is full grown. On most shrubs this is best done during dormancy (in the fall or winter when the plant has no leaves). The exception is plants that bloom on their previous year’s growth, like Lilac or Forsythia. These shrubs should be sheared just after flowering in spring. Either way, what you need to do is cut the plant back to just above the previous year’s cut. You can see where this is because there are forks in each branch where it was cut before.
Our pride and joy is the giant Limelight Hydrangea in our front yard; it’s like a giant ten-foot snowball after years of regular shearing. We have a row of “Limemound” spirea in our garden; their new foliage glows neon green in the early spring if the plants are sheared back. Our “Pinky Winky” hydrangeas, planted only a few years ago, are five-foot powder puffs covered with creamy pink cones that look good enough to eat.
Don’t be afraid to trim or shear flowering shrubs. You can cut them back to about half without harming them in any way, and you’ll be rewarded with a much tidier, more compact shape as well as much heavier bloom. At the same time you should scatter some fertilizer around the base of the plant (we use Espoma Plant Tone). Regular watering helps, too. If plants get too dry or hungry during the growing season the flowers will be much smaller.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.