Clematis

Armand clematis is a vigorous evergreen climbing shrub native to much of China (except the north and extreme south) and northern Myanmar, grown for its profusion of almond-scented, star-shaped white flowers in early spring (March-April) on the previous season's wood. It excels as a structure-covering climber on sheltered walls, pergolas, and fences, providing year-round glossy, deep-green foliage. The honest catch is its rampant vigor: in a favored site it can overwhelm host structures within a few years, sheds masses of dead leaves through the year (a persistent litter problem), and all parts are toxic to cats, dogs, and horses (and the sap irritates skin) - and it is only reliably hardy to about USDA zone 7b with the shelter of a warm wall, making it a borderline plant anywhere colder.

The classic large-flowered garden clematis - represented here by the iconic Jackman hybrid (Clematis x jackmanii), a deciduous twining vine bred in England in 1858 and still the benchmark for the group. It carries an abundance of showy, four-sepaled violet-purple flowers 5 to 7 inches across from mid summer, climbing 7 to 10 feet on a trellis, arbor, or fence. The classic gardener rule applies: roots in cool shade, flowers in the sun.

Mountain clematis is a vigorous deciduous climber native to the mountains of Asia from Afghanistan east to Taiwan, ascending through the Himalayas and China. In temperate gardens it smothers walls, fences, and large trees with a breathtaking flush of white or pale-pink four-petalled flowers in late spring, covering itself so densely the foliage disappears. The honest catch is its sheer vigor: left unchecked it reaches 39 feet and can engulf adjacent shrubs or lift roof tiles, and like all clematis it contains protoanemonin - a skin and mucous-membrane irritant - in its sap and leaves, making it toxic if ingested.