Spiraea tomentosa is an erect shrub with stems unbranched (unless damaged) and usually less than one meter tall. The leaves are simple, alternate, 3 -7 cm long, 1-3 cm wide, with toothed margins (margins may be entire toward the base of some leaves). The adaxial (upper) leaf surface is dark green and the abaxial (under) surface is covered by tomentose (dense wooly), often tan hairs. The flowers each have 5 pink or rose-colored petals, each tapering quickly toward the base. The calyx is fused at the base with 5 broadly triangular lobes. The entire calyx, and the branches of the inflorescence are covered by a dense growth of tomentose (usually tan) hairs. The flowers are aggregated into a long pyrimidal shape at the tip of the stem. The fruits are dry, brown follicles opening broadly at the tip when ripe and long-persistent on the stems.

Spiraea tomentosa is widely distributed throughout the interior of Wisconsin, but is apparently absent or at least uncommon in the southern and eastern counties, along the western boundary north to St. Croix County and also in the area bordering Lake Superior. It is found most commonly on sunny sites, in moist to wet soil.