Petasites japonicus

The Japanese Butterbur or Petasites japonicus is a vigorous trailing perennial plant found in shaded areas and humid environments. Its globular flower heads rest on a collar of pale green bracts and grow upwards into spikes adorned with small, fragrant cream-coloured flowers in spring before the appearance of large luxuriant leaves. Interesting for bringing a bit of luxuriance to a large garden's shady, inhospitable wet areas, its tendency to spread must be contained. This plant prefers humus-rich soils and dislikes scorching sun.

The Petasites japonicus is a plant native to China, Korea, and Japan. This perennial forms a strongly carpeting clump that reaches up to 1.20 m (4ft) in height and spreads without any theoretical limit over time through its robust trailing rhizome—the plant blooms in March-April before the appearance of the leaves. Emerging from grey leaves, the flower head emerges from the ground, borne on a leafy stem. On this stem, the leaves are alternate, elongated, pointed, and sessile, very different from the large basal leaves that appear after flowering. The flower head forms an elliptical and compact cluster, 10 to 25 cm (4 to 10in) tall. It consists of small female or male heads gathered in panicles. The pale green and white flowers, surrounded by light green bracts with a diameter of 1 cm (0in), emit a sweet scent reminiscent of honey. The basal, deciduous foliage appears at a later stage. It comprises large kidney-shaped leaves with a rounded, veined, undulate margin, reaching 40 cm (16in) in diameter. Their colour is a satiny greyish green, and they are downy on the upper surface. They are bordered by a dentate margin and are attached to the rhizome by a long petiole that is often consumed as a vegetable in Japan.

The Japanese Butterbur is a fast-growing plant, helpful in bringing a luxuriant touch to the boundaries of a very large garden to cover a ditch, a fresh rockery, or even a neglected, humid understory. However, care must ensure it does not exceed the allotted limits. Since it loves humidity and dislikes the sun, it can be easily contained by placing a dry rockery in its path, where the sun prevails over the shade. It can be paired with American Skunk Cabbage, Yellow Flag Iris, Solomon's Seal, and well-established Peonies.