"Artemesias Dress the Garden in Silver"

by Carolyn Singer, Foothill Cottage Gardens
Fine Gardening, July/August 1995

I wonder if any gardener, seeing sunlight catch the beautiful silver luminescence of artemisia leaves, or noting how the colors of nearby flowers are intensified by their gray glow, could resist planting a few. Each one that I have added to my rock garden and my herbaceous border has pleased me, and most of them, with their strong herbal fragrance, have gone untouched by the deer who forage there frequently, Gardeners everywhere will love that! Artemisias are more than just "lace"—accessories to garden centerpieces: they are beautiful and functional all by themselves.

Most artemisias are strong growers ideally suited to hot, sunny, dry exposures, and rocky or poor soil, Many will also thrive in cool, foggy coastal climates, and all the artemisias covered here are cold hardy at least to USDA Zone 4 ( -30°F).

There are hundreds of artemisias, including some annuals but it is the ornamental perennials that are garden-worthy. These plants have a tarnished reputation despite their dependability and the value of their silver foliage. The flowers are not attractive in some species, many are too aggressive to include in borders, and in hot, humid weather, the foliage of some may wilt. However, there are many artemisias without these drawbacks, and special attention to growing conditions and varietal choices will ensure success with this wonderful plant.

Very adaptable artemisias

Four of my favorite artemisias are good garden plants in a wide range of climates, from the mountains of northern California, where I garden, to the deep south. All four tolerate weekly irrigation in my clay soil and still look as beautifully silver as those plants growing in dry conditions.

'Powis Castle'—This plant is shrubby but very delicate. It grows up to 2 feet high and 4 feet wide. The finely cut foliage of this non-blooming cultivar is a perfect background for 'Autumn Joy' sedum or any perennial 2 to 3 feet high. Tall alliums, such as A. sphaerocephalum 'Drumsticks' or A. caeruleum are especially striking next to it. 'Powis Castle' may also be used as an accent near taller shrubs because of its neat, mounding growth habit.

'Powis Castle' will grow in any but a highly enriched soil. To keep the plant dense and compact, keep it pruned all summer. I prune mine back only once a year, in late winter, leaving short ( 12 inches) woody stems with lots of buds. I don't prune in summer, so my plant is spreading but full.

A. ludoviciana—The cultivar 'Valerie Finnis' grows 18 to 24 inches tall and has broad leaves that, in a certain light, appear to be almost white. I grow it just behind alpine asters in one of my borders, providing a foil for the violet of the asters' daisylike spring flowers. In midsummer, when it begins to look rangy, I cut it to the ground. By August it reappears at a lower height and contrasts exquisitely for the next three months with the glowing blue-violet flowers of Aster x frikartii.

In my clay loam, the spread of 'Valerie Finnis' is not aggressive, but in sandy soils it grows more rapidly and needs to be kept in check. Hardy to Zone 1, where winter temperatures may fall below -50°F, 'Valerie Finnis' is also an ideal drought-tolerant plant for warmer areas (to Zone 9 [20°F]) with little moisture in winter. 'Silver King' (photo, below) is another fine cultivar hardy to Zone 3 (-40°F).

A. versicolor—This petite artemisia is delicate and lacy. It is so striking it brings visitors in my garden to a stop. The plant spreads to 3 feet and has a maximum height of 12 inches. Its pale gray curly leaves have a blue-green cast, but it looks quite silvery in bright light when grown in dry soil. The foliage is unusual and dries beautifully for wreaths. I grow this low artemisia near ornamental grasses, especially blue oat grass (Helictotrichon sempervirens), for an echo of its foliage color.

A. stelleriana—Beach wormwood. also known as old woman or dusty miller, is one of the best rockgarden artemisias and a standby of Southern gardeners near the coast. 'Silver Brocade' is a choice cultivar with soft, felt-like leaves. Its size, 3 to 4 feet wide and under 1 foot tall, makes it a wonderful ground cover or edging plant for dry areas. The blooms are not valuable, but they do not detract from the plant. Deer will occasionally browse on this species, perhaps because it does not have the strong, herby odor that other artemisias do.

The peach-pink flowers and bright green foliage of twinspur (Diascia vigilis) growing next to 'Silver Brocade' are a highlight in my rock garden for months. In early spring, miniature narcissus bloom near the newly emerging artemisia, contrasting with its tight, mounded appearance.

An artemisia for cool climates

A. frigida—Fringed wormwood is native to the northern Rockies and Great Plains and also grows in Siberia, yet it does beautifully in my Zone 8 garden, where temperatures rarely go below 10°F. It has very fine foliage and looks good in my rock garden even in winter, when rains are heavy and the clay soil does not dry out until spring.

Its slightly curved, 18-inch tall flower stalks rise from a low mat of leaves. The stalks are attractive dried for wreaths and arrangements. I leave the stalks on until they start to flop over, and then I hang them up to dry. This artemisia is not an aggressive grower. The creeping mat spreads slowly, making an appealing perennial that requires little maintenance.

Taller artemisias

Two striking artemisias for the tall mixed border differ from the other artemisias in foliage color and growing requirements.

A. absinthium 'Lambrook Silver'—If left uncrowded by nearby plants, 'Lambrook Silver' wormwood is delicate and airy. It is stunning when contrasted with red or bronze foliage. It grows to a height and spread of about 3 feet, but the base of the plant stays narrow. 'Lambrook Silver' is beautiful during the entire summer and even into fall, when its flower stalks add texture to the landscape.

A. lactiflora—White mugwort grows even taller than wormwood—up to 7 feet. I was once amazed by a huge stand of it at the governor's perennial garden in Vancouver, British Columbia, in August. Fragrant, creamy white flowers hanging in panicles contrasted with rich green foliage. The mugwort had spread to cover an area 5 by 10 feet in size. Paired with Rudbeckia 'Goldsturm' this artemisia had everyone's attention. In my own garden, mugwort grows to about 3 feet tall, seems to prefer the irrigated border and afternoon shade, and spreads very little. While some gardeners have reported deer damage, it has never been browsed in my garden.

Low and refined artemisias

A. schmidtiana 'Silver Mound'—The popular artemisia known as silver mound requires good drainage. Mine has done best in very poor, rocky soil on the edge of my dry rock garden. When I tried it as an edging plant in richer soil, or where it was irrigated weekly, it eventually died. It forms a low mound (under 6 inches tall) of soft, silver foliage. I have seen it grow taller in more fertile soil, but then in midsummer it needs to be cut back to keep it attractive, and it will not survive for more than a few years. I cut only the bloom stalks off my silver mound, and I enjoy its silky foliage all summer.

A. caucasica (A. assoana) My alpine wormwood grows at the top of a wall, where it spills over in a tight mat, hugging the rocks. Its soft filigreed foliage invites touching. Since it is evergreen here in Zone 8, it highlights the winter rock garden. Its blooms are 3-inch tall, gray-green spheres that add interest all summer. The plant’s height is under 3 inches, and the spread in two years has been 14 inches. In this short period, it has become my favorite species because of its beautiful growth habit and ease of culture.

Culture and propagation of artemisias

While gardeners in the south do not have the ideal conditions for growing artemisias, these plants will adapt to many garden environments. Full sun is a requirement for optimal foliage growth and color (except in the case of A. lactiflora). Western and southern exposures, and areas that enjoy reflected heat from walls, rocks or buildings, offer the perfect microclimates. Soil may be amended, but should not be too rich: a handful of rock phosphate will boost root growth. Compost and/or gravel may be added to heavy clay soils to improve drainage—especially important in winter. Soils that are saturated with frequent rains usually need the addition of gravel to improve drainage. After planting, small rocks and gravel are the perfect mulch on the soil surface.

Virtually all artemisias can propagated by cuttings taken in late spring or early summer before stems elongate and the plants try to flower. Since 'Powis Castle' does not bloom, cutting material is available anytime during the spring or summer. If you cut back 'Valerie Finnis’ and 'Silver Mound' to prevent them from blooming, you'll have a continuous supply of new shoots from which to take cuttings throughout the summer and into fall.

Artemisia cuttings should never kept too moist, or they will rot before roots have sprouted. I recommend a fast-draining medium, such as a half-and-half mix of perlite and vermiculite.

You can easily divide all artemisias—except 'Lambrook Silver' and ‘Powis Castle’, which seems to resent transplanting -- in spring as soon as growth begins. Gardeners in mild climates can also take divisions from the parent plants in fall.

Limitless versatility

Artemisias fill so many roles that you can hardly go wrong, no matter how you choose to use them. Their elegant silver adds a highlight to perennial borders and rock gardens unmatched by other perennials chosen for their color. A less demanding plant would be difficult to find.

Best of all, artemisias perform all season long. ‘Silver Mound’ contrasts early in the year with the bold, dark green foliage of purple coneflower (Echinacea purpurea) and later with its pink flowers. The form and foliage of ‘Powis Castle’ artemisia provide a backdrop for spring bulbs, a foil for the glowing hues of penstemons in midsummer and, at season’s end, a lovely contrast for the rich copper brown of ‘Autumn Joy’ sedum. While many perennials in the border bloom and fade, artemisias provide a definition, a strength and sometimes an ethereal quality for many months.