False Spirea

Sorbaria sorbifolia, false spirea or Ural false spirea, is a deciduous shrub native to Siberia, northern China, and Korea, named for its pinnate, ash-like foliage (Sorbaria shares the leaf pattern of Sorbus, the mountain ashes, without being closely related). Large, upright, creamy-white flower plumes — astilbe-like in shape — cover the shrub for several weeks in mid-to-late summer, a season when few other shrubs are still flowering. It is exceptionally cold hardy, tolerating winters into Zone 2, and adapts to nearly any soil, including wet or poor ground that would struggle most other ornamental shrubs.

That same toughness is its biggest liability: false spirea spreads aggressively by root suckers, quickly forming a dense colony that keeps expanding outward well beyond its original planting hole, and it has escaped cultivation into natural areas in parts of the northern US and Canada, including documented invasive spread in Alaska and the Northeast. Plant it only where unlimited suckering spread is genuinely wanted — mass plantings, slope and erosion control, or a naturalized screen with room to fill in — and never in a small foundation bed or border where it will need constant digging out to stay contained. A buried root barrier around the planting area is the only reliable way to keep it in bounds in a smaller garden.