How to Prune Magic Carpet Spirea
Magic Carpet spirea (Spiraea japonica "Walbuma") brightens a garden with rosy-pink flowers set against a background of bright, yellow-green leaves. Magic Carpet is regarded as a low-maintenance plant but benefits from pruning to rejuvenate its growth and to maintain its appearance. Hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, this compact shrub reaches an average size of 18 to 24 inches tall by 24 inches wide and requires full-sun exposure. It is used as a low border shrub and in the foreground of flowerbeds.
Magic Carpet responds well to pruning and quickly produces new healthy growth. An annual hard-pruning in late winter or early spring can help the shrub. Pruning should be completed before the final frost and before the plant forms new buds so that during the growing season it has a neat, uniform shape without any old, unattractive branches. Additionally, light pruning can be performed annually at the end of the shrub's blooming period in late spring to early summer to clean up expired blooms and maintain the plant's shape.
The best tool to use for annual hard-pruning is small hand pruners so you can assess the health of stems as you prune them individually. Magic Carpet's stems are thin so do not require the use of larger tools such as lopping shears and a pruning saw. Hand shears work well for cleaning up the plant after its blooming period and allow you to trim the entire plant quickly. Because the hard-pruning session just a couple months earlier requires careful inspection, such close inspection of stems after the shrub finishes flowering isn't necessary.
All pruning tools should be disinfected before you begin pruning; disinfect them again after pruning diseased branches. Soak the blades in a solution of diluted bleach -- one part bleach to nine parts water -- for about 10 minutes before wiping them clean and rinsing them with water. Alternatively, spray the blades thoroughly with the diluted bleach solution from a spray bottle, and allow the solution to sit on the blades for about 10 minutes before rinsing the blades with water.
Magic Carpet spirea can handle pruning of up to two-thirds its total height, but such a severe pruning may not be necessary if the stems appear neat and relatively healthy. Estimate the amount of pruning required visually, or measure the tallest stems for more accurate pruning. Cut each stem back to about 1/4 inch above a healthy bud, leaf node or intersecting branch; a bud is a small bump that will develop a flower or stem, and a leaf node is a small bump that will develop a leaf. Repeat the procedure throughout the entire plant to give it a uniform shape. If you notice signs of disease or damage, usually indicated by dead or black stems, then cut them to the ground. An old plant may require rejuvenation pruning over a period of three years so it grows completely new branches. In the first year, cut one-third of its total branches to the ground, and repeat that task with another one-third of the old branches in the second year. In the third year, cut back the remaining one-third of the old branches.
Shaping after Blooms
Magic Carpet spirea does not require pruning after its blooming period, but pruning at that time helps maintain a neat appearance in the vigorous grower. After the last blooms expire, shear off the tips of the stems just below the spent flowers. Cut back as much as one-third of each stem's length if the plant appears unkempt or overgrown. If you have trouble giving the shrub a uniform shape by using large garden shears, then use smaller grass shears or hand pruners for better control.