The Best Ways to Split a Spirea Bush

Growing Spirea

• Fast-growing deciduous shrubs valued both for their graceful forms and flowers, spireas grow best in partial to full sun -- the sunnier the better for best flowers. Spireas don’t like wet soils but otherwise tolerate many soil types, although rich loamy soils are ideal. Mulch shrubs well to retain soil moisture and make sure they get water in the summer. Prune bridal wreath-type spireas after they flower, cutting weak or old canes all the way to the ground. Wait until winter or early spring to lightly prune the lower growing shrubby spireas. Remove flowers after they fade to stimulate a second flush of growth and bloom.

Crown Division

• Established shrubs can get overgrown and lose vitality. Dividing shrubs can quickly reinvigorate them, but it should only be done when they are dormant. Crown division offers the opportunity to cut out old growth while creating new large, well-rooted shrubs. Loosen the soil around the entire shrub and carefully lift the shrub clump, removing some soil from roots. You may need a sharp garden spade or hatchet to cut the crown into quarters or smaller sections. Cut away and discard old root sections -- the narrow tip of each root section -- and replant the rest. Before planting, prune any damaged roots and cut back woody stems.

Sucker Division

• Spirea shrubs also produce suckers from their roots. These individual rooted shoots emerge from large underground horizontal roots that extend out from the parent plant. In time each sucker will grow into a new shrub, but you can establish a large, vigorous shrub more quickly by planting several suckers together. Make sure suckers have a sufficient independent root system before you separate them. Dig up just enough of the parent’s roots to separate the plants. Use pruners or a sharp shovel blade to sever the root connecting the parent to the sucker. Keep as much soil as possible around the roots when transplanting suckers.

Other Propagation

• You can also propagate spirea by simple layering, or bending a long, flexible stem into a loose U shape and burying the bend underground to generate a new, separately rooted plant. New spirea shrubs can also be propagated from rooted cuttings -- both softwood and hardwood. For softwood cuttings -- generally quickest to root -- take new growth before it gets woody, usually by mid-summer. Take hardwood cuttings in late fall or early winter when plants are dormant, after at least one hard frost. Root both types of cuttings in sterile potting soil. Some spirea shrubs, particularly Japanese spireas, reproduce aggressively from seed. In fact, in moist temperate climates they are considered invasive. Once established in disturbed areas they make their way to meadows, stream banks and open areas in forests, developing in dense stands that choke out native plants.