The artemisia group of herbs encompasses several silvery-grey foliage plants, including mugwort, common artemisia, wormwood, tarragon and southernwood. Though varying in height from the ground-hugging dwarf wormwood to the towering southernwood, artemisias share a pungent scent and a filigreed, silvery appearance. Gardeners utilize this delicate foliage and ethereal color in moon gardens, to sooth a hectic color scheme and for breaking up the monotony of green foliage.
Choose a sunny site in an area of the garden not prone to water runoff or puddles. If necessary, build a slightly raised bed to accommodate the herbs, which can't tolerate wet or moist soil. The only exception is the almost treelike white mugwort (Artemisia lactiflora), which prefers moist soil and will grow well in either sun or part shade.
Artemisias prefer light, dry soil. If the patch in which you plan to grow the herbs is on the normal to clay side, add sand or gravel for drainage. Again, white mugwort represents the exception to this rule; plant this 5-foot artemisia where its soil will remain consistently moist, or where you can easily water it.
Position artemisias where they will do the most good---and avoid placing them where they can harm other plants. Herbalist Lesley Bremness suggests keeping wormwood away from sage, caraway, anise and fennel, because wormwood exudes a substance which can inhibit the growth of these plants. Onions and carrots, on the other hand, may benefit from wormwood's proximity, because its pungent scent confuses the flying pests which feed on them. Similarly, wormwood and southernwood work well in orchards to repel the fruit tree moth, and by the cabbage patch to deter cabbage moths.
Set artemisia seedlings 18 inches (smaller varieties) to 36 inches (taller varieties) apart in prepared soil. If growing from seed, thin to the proper spacing when the herbs are several inches tall. Do not mulch with plastic or heavy wood chips, which potentially create too much moisture for the dry soil-loving herbs. Stake southernwood and other tall herbs if the garden spot is prone to high winds.
Watering and Feeding
Rainfall usually provides enough moisture for artemisias. If they seem to be wilting during unusually dry weather, give the soil a thorough soaking. While the carefree plants don't need fertilizer to thrive, a nitrogen-rich feeding in early spring will encourage more vigorous foliage growth. Lay 1 to 2 inches of aged manure in a circle around the plants, or water the foliage and soil with liquid fish emulsion.
Cutting back artemisias helps protect the herbs from winter damage. In autumn, prune the herbs back by at least 1/3. For southernwood, however, an early spring pruning in which only the dead-looking growth is removed is the best practice, according to Bremness.