Powis Castle artemisia is a woody, evergreen plant. This species produces silvery-green foliage with a greener hue in spring and summer that turns more silvery during the colder months. Powis Castle artemisia is not grown for its flowers, which rarely occur, but for its foliage, which has an unusual color and strong fragrance. It grows in short, dense mounds up to 3 feet (1 m) tall and up to 6 feet (2 m) in diameter.
There are around 400 species of artemisia, and Powis Castle is actually a hybrid variety. It is believed to be a cross between Artemisia arborescens and Artemisia absinthium. Being a hybrid variety, Powis Castle artemisia does not produce viable seeds, so new plants can only be produced from stem cuttings or by dividing the roots of mature plants. Flowers are rarely produced and, if seeds from these flowers are used, there is a considerable chance that they will not germinate. If the seeds do germinate, the result will be a second generation hybrid that will most likely be unstable with negative characteristics.
Believed to have originated at Powis Castle in Wales in the United Kingdom in 1972, this species is tolerant of a wide range of environmental factors. Powis Castle artemisia can tolerate most soil types and still thrives in areas of high humidity, high summer temperatures and periods of hard frost. It is also tolerant of periods of drought but is not tolerant of periods of waterlogging. This encourages a variety of root rot infections.
Powis Castle artemisia is prone to a considerable number of bacterial and fungal diseases, such as mildews, rusts, leaf spots and root rots. If kept in good general health, this species is less likely to contract infection. A gardener can minimize the risk of fungal and bacterial infection by regularly removing dead leaves and plant matter from the area around the plant, because diseases and insects can lay dormant in dead garden matter.
This species is also prone to attack from gall midges and aphids. Gall midges are tiny, hairy maggots that turn into flies as they mature. Feeding on the stems of the Powis Castle artemisia, gall midges cause foliage to wilt and die back. The feeding sites are open to infection and disease, and, if left untreated, the plant may die. This can be a serious issue for lovers of this species, because seed is not available, and plants are often hard to find and quite expensive.