Artemisias are a species of Mediterranean herbs distinguished by their silver, white or gray foliage. There are over 300 different species of artemisia. Most artimisias are referred to as mugworts, white sages or wormwood, except for tarragon, which is also a type of artemisia. Artemisias make wonderful borders for flower and vegetable gardens, and although many can become invasive if left to their own devices, several cultivars, namely Silver King and Silver Mound, form very slowly, spreading tidy mounds. Artemisias don't need much in the way of winter care.
Shear off faded flower stalks in late summer or early fall.
Remove dead or broken branches. Make the cuts 1 to 2 inches into live wood at a 45-degree angle above a strong branch or bud.
Mound 3 to 4 inches of mulch around the base of the plant and over the root zone. This prevents frost heave (roots are exposed due to soil expanding and contracting during thaw/freeze cycles) and protects the roots from freezing.
Give your artemisia 1 to 2 inches of water a week during the fall. Stop watering two to three days before predicted freezing weather.
Divide your artemisia. When the center becomes woody and open and the plant starts to flop to the sides, dig up the plant, removing as much of the root ball as you can. Divide the plant into three to four sections, removing the vigorous outer growth from the woody center. Replant the sections as normal and discard the center. You may only need to divide artemisia every three to four years.