It’s easy for home gardeners to double or triple the number of blooms on flowering shrubs like lilac, hydrangea, spirea and weigela. All that is needed is regular mowing once a year, especially when the plant is young, and regular feeding. There is a technique for doing this, and a reason why it works so well.
When woody plants are sheared or pruned, they “fork” just below the cut. At least two but up to five new branches will grow along the stem, each with a “growing tip” or bud at the end. Most woody shrubs flower on their new growth, so the bud is a flower bud.
Young shrubs usually have only a few branches coming from the base of the plant, and these branches tend to become long and lanky if left unpruned. Often the weight of the flowers will then cause these sucker branches to sag. Pruning young shrubs each year will encourage better branching habits and a more mounded shape, as well as stronger branches that won’t sag.
Good nurseries regularly mow young shrubs several times during production. They call it “box cutting” or “back shearing” because the first thing the plant does after shearing is “flush” or sprout a bunch of healthy new shoots. Nurseries time this selling season because freshly flushed shrubs look nice and fluffy and start to produce flower buds, making them easier to sell.
Once the shrub is in your garden, you should continue this practice every year until the plant is fully grown. On most shrubs, this is best done during dormancy (in fall or winter when the plant has no leaves). The exception is plants that bloom on their previous year’s growth, such as lilac or forsythia. These shrubs should be pruned right after flowering in the spring. Either way, what you need to do is cut the plant just above the previous year’s cut. You can see where it 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 steady shearing. We have a row of ‘Liemound’ spirea in our garden; their new foliage turns neon green in early spring if the plants are sheared. Our “Pinky Winky” hydrangeas, planted only a few years ago, are five-foot puffs covered in creamy pink cones that look good enough to eat.
Don’t be afraid to prune or mow flowering shrubs. You can cut them down by about half without damaging them in any way, and you’ll be rewarded with a much neater, more compact shape as well as a much heavier bloom. At the same time, you should spread some fertilizer around the base of the plant (we use Espoma Plant Tone). Regular watering also helps. If the plants get too dry or starved during the growing season, the flowers will be much smaller.
Steve Boehme is a landscaper/installer specializing in landscape “metamorphoses”. “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.
This drawing shows how annual shear multiplies the number of branch tips and blooms on flowering shrubs.