May’s weed of the month is an aggressively spreading, thorny plant. Multiflora rose (Rosa multiflora) is native to eastern Asia. It was introduced to North America as a rootstock for ornamental roses, and for erosion control, living fencerows, and wildlife habitat. Because of its highly invasive nature, it escaped cultivation and has become a serious threat to habitats where it outcompetes native plants and desirable agricultural forages.
Multiflora rose is a multi-stemmed, bushy shrub with long, thorny stems. The stems can grow up to six feet tall, and spread horizontally up to 15 feet. Stems are green or reddish in color with stiff, curved thorns. Leaves are compound and divided into 5-11 leaflets. The leaflets are one-two inches in length. Clusters of showy white flowers are produced in May and June, and have a distinct rose fragrance. The flowers produce rose hip fruits that turn bright red and contain several seeds that persist throughout the winter.
Multiflora rose can invade many types of habitat. It has been recorded in forest understories, hedgerows, savannas, stream banks, wetland and bog edges, pastures, roadsides, and other disturbed habitats. In Minnesota, it is commonly found in the southeastern part of the state and is spreading northward. It can invade new areas through seed dispersal when animals consume the fruit and spread the seed, and it also spreads by the elongated stems rooting to the ground.
Because of its ability to root from stems, multiflora rose can form thick, impenetrable thickets. The stems can also climb trees, shrubs, and structures that make it difficult for humans, wildlife, and livestock to navigate. Its invasive growth habitat prevents the growth of native herbaceous and woody plants.
Management of multiflora rose requires a multi-year commitment.