How to Grow and Care for Artemisia

The genus Artemisia contains about 300 species. Although it is part of the Asteraceae (daisy) family, you will not see a lot of showy flowers with the Artemisia species. The genus includes annuals, perennials, and even woody shrubs, but those cultivated for garden use are mostly herbaceous perennials.

Most garden artemisias are grown as foliage plants, valued for their filagree-like leaves and their tolerance for dry, sunny locations. Commonly known as artemesia, individual species also may be known as wormwood, absinthe, southernwood, and mugwort. Artemisias have alternate leaves in various shapes, often lobed and covered with whitish hairs that give them a silvery, grayish look. Their non-showy flowers, often clustered in panicles but sometimes single, are small (1/16 to 3/8 inches), white or yellow, and cylindrical.

Artemisias are typically planted from nursery-grown plants in the spring as soon as the soil can be worked, but this sturdy plant can be planted almost any time. It will grow quickly, achieving full size within a couple of months. Established clumps will return quickly each spring.

Some caution is warranted, as some species of Artemisia, such as tarragon, are considered highly toxic to pets. For humans, many species are mildly toxic.

Artemisia Care

Artemisias are relatively low-maintenance plants, but they do have some preferences when it comes to growing environment. They will grow best in a full sun location, although most varieties can handle part shade. Most types like dry to medium-moisture soil—well-draining soil is essential. These plants are among the best at tolerating dry soil and drought conditions.

Beyond this, there is little care required with these plants. Perhaps because of the powerful scent many species have, they are largely immune to common insect pests.

Warning

Some artemisia species are considered invasive in some parts of the U.S. Check with a local expert before planting them, and take care to prevent your plants from escaping into surrounding areas. Named cultivars are often less invasive than the pure species plants, so it's a good idea to do some research before choosing a variety. For example, mugwort (Artemisia vulgaris) is a two- to four-foot tall plant with greenish-white blooms that appears in mid to late summer. It can be grown in zones 3 to 8, but it is considered a noxious weed in much of the Midwest.

Light

Artemisias grow best in full sun, but some types will tolerate some shade, provided they receive about six hours of sun.

Soil

With a few exceptions, such as Artemisia lactiflora, which likes moist soils, Artemisias need well-draining soil on the dry side within a soil pH range of 5.5–8.0. If left sitting in damp soil, they will decline and/or be short-lived.

Water

As with most silver-leaved perennials, Artemisia plants are very drought tolerant, considered ideal for dry, sunny sites. They will need regular water until the plants are established, but they can take care of themselves after that. Except in prolonged drought, they rarely need supplemental watering.

Temperature and Humidity

Most Artemisia species are hardy in USDA cold hardiness zones 4 to 8 or 9, but there are some that can be planted as far north as zone 3 and as far south as zone 10. The varieties offered at local garden centers will generally be appropriate for your climate. Most artemisias do equally well in arid and humid atmospheric conditions, provided soil moisture is on the dry side. Some species can be prone to fungal rust and powdery mildew in humid conditions.

Fertilizer

Artemisias do not like overly rich soil. No supplemental fertilizer should be necessary, especially if you are regularly adding organic matter to your beds. Too much nitrogen tends to cause stems to become leggy and ungainly.

Types of Artemisia

Several popular Artemisia species are known by other common names: southernwood (A. abrotanum); wormwood, also called absinthe (A. absinthium); mugwort (A. vulgaris); sagebrush (A. tridentata); and the culinary herb called tarragon (A. dracunculus). But those used as landscape plants are often named cultivars or hybrids that are sold simply as "artemisia." Here are some common varieties popular for landscape use:

• Artemisia abrotanum (southernwood) is two- to four-foot shrub-like species with grayish green foliage. It is hardy in zones 4 to 8.
• Artemisia californica'Canyon Gray', also known as canyon sagebrush, stays under two feet in height but can spread as much as ten feet, making it an excellent ground cover. It is hardy in zones 7 to 10.
• Artemisia'Powis Castle' is a hybrid variety, an upright plant growing two to three feet tall with silver-gray fern-like foliage. It can be grown in USDA zones 6 to 10.
• Artemisia ludoviciana'Silver Queen' is a fast-spreading variety with bright silver-white leaves that turn reddish in fall. It grows up to four feet tall and is hardy in zone 4 to 9.
• Artemisia stelleriana'Silver Brocade' is a low-growing six- to eight-inch tall plant that spreads about one foot. It has wooly white leaves and is often used in containers or planted into crevices of retaining walls. It is hardy in zones 3 to 9.
• Artemisia versicolor'Seafoam' is a ground-hugging eight-inch variety with billowy silver foliage; it is hardy in zones 4 to 10.
• Artemisia schmidtiana'Silver Mound' forms one-foot mounds of soft-textured light green foliage. This variety is hardy in zones 5 to 10.

Pruning

Perennial artemisias can be cut back in the fall or spring. Shrubby varieties should be pruned back hard, to a point just above the lowest growth nodes—don't cut them back flush with ground level. Non-woody artemisias can get floppy, especially after flowering. Shear them in midsummer to prevent them from splitting open down the middle.

Propagating Artemisia

New plants can be started from seeds, divisions, or cuttings, but many of these plants are hybrids that are either sterile or produce seeds that do not grow true to the parent plant. Thus, propagation is most often done by simple division of the root clumps, which offers the fastest, most trouble-free method. Here's how to do it:

1. In spring or fall, use a shovel to dig up the entire clump.
2. Using a spade or sharp trowel, divide the root ball into sections, each having a healthy section of roots and crown eyes.
3. Replant the pieces immediately, with the crown just barely covered with soil.
4. Water regularly until established.

For the health of the plant, it's best to divide every two to three years or when you start to notice the center beginning to die out.

How to Grow Artemisia From Seed

Pure species plants will produce seeds that grow true to the parent plant but hybrids (which includes most cultivated garden plants) do not. But because simple root division is so easy, seed propagation isn't practiced very often. Even when purchasing this plant from online retailers, you will usually receive either live plants or root sections to plant.

However, if you are purchasing commercial seeds—which might be the only way to obtain some species, such as absinthe—they can be started indoors or direct-sown in the garden in spring or early summer. Plant the seeds about 1/2 inch deep and keep them moist in a sunny location until they sprout. Seedlings will take 90 to 120 days to mature into flowering plants.

Potting and Repotting Artemisia

Artemisia makes a good container plant to add a gentle aroma to a sunny deck or patio. It's best to use a very porous potting mix, such as cactus/succulent mix, in a container of any material, provided it has good drainage. Standard peat-based potting mixes retain too much water and sometimes can encourage root rot with this plant.

Rather than repotting plants into larger containers, you can simply divide the plants every couple of years, replanting one piece in the original pot and discarding the rest or using them for propagating new plants.

In cold regions, potted artemisia plants should be moved into a protected location for the winter. A cold frame or an unheated porch or garage makes a good sheltered location for the winter.

Overwintering

If planted in an appropriate USDA zone, artemesia needs little in the way of winter protection. In either fall or the following spring, you will want to shear back the plants to just above the growth buds (not all the way to ground level).

Common Pests & Plant Diseases

If the conditions are ideal, artemisias are quite resilient. Because of their strong scent, insects tend to avoid artemisias. But they can be prone to many fungal and rust diseases, like white rust, powdery mildew, and downy mildew. Hot, humid weather exacerbates these problems. Growing them in an open area with good airflow will help mitigate the problems.

How to Get Artemisia to Bloom

The tiny flowers that bloom in late summer or fall on most species are not at all showy, so lack of flowering is not considered a problem. In fact, many gardeners pinch off the flower buds to allow the plant to put its energy into growing its foliage.

Common Problems With Artemisia

These are remarkably problem-free plants, but gardeners who make an ill-advised choice of species are sometimes alarmed by the rampant spread within the garden and sometimes beyond. Generally speaking, the named cultivars are less invasive than the pure species, but some of the pure species plants can take over a garden rather easily. The biggest offender is A. vulgaris (common mugwort), which has demonstrated its invasiveness throughout most of the U.S.—even its named cultivars are renowned for their aggressive spread. Should you find that you've selected one of the badly behaved artemisias, it's best to dig up your plants and look for an alternate species that has better manners.

Artemisia planted in dense, wet soils can readily develop root rot. Discard affected plants and choose another location or amend with plenty of sand before replanting.

From: thespruce