Microbiota decussata: A Versatile

Nancy Rose

decussata is an elegant, low- arborvitae), but the two are different enough to evergreen that is finding maintain their separate designations. ~/-L /~V1 /icrobiota growing its way into more gardens every year. With a height at maturity averaging only ten Its combmation of graceful form, attractive foli- to eighteen inches in most landscape plantings, age, cold hardiness, and landscape value earned the ’s low, widespreading form resem- it a 1998 Cary Award, which annually honors bles that of spreading . (Interestingly, outstanding woody for New England native Siberian specimens with heights ranging gardens. Microbiota decussata has gamed favor from eight inches to over three feet have been well beyond New England, however, and gar- reported, indicating that it may be possible to deners in many states may find it an excellent select shorter or taller types from wild popu- addition to their landscapes. lations.) Many long stems radiate horizontally This unique conifer has a remote and limited from the plant’s crown, creating a spread that native range: the Sikhote Alin mountain range can reach ten feet or more. As these main in the southeastern leg of Siberia, bordering the stems grow outward, numerous gently arching Sea of Japan. It is often found growing above secondary branches rise from them, develop- the treeline, frequently in association with ing first near the center of the plant. Since all of Pinus pumila, a shrubby pine species, and in Microbiota decussata’s branch tips nod down- shrubland areas m the upper mountain valleys ward, the result is a wonderfully graceful, softly of the region. The species was first recorded by layered appearance. The nodding branch tips are botamst I. K. Shishkin in 1921, in the mountains characteristic of the species and make it easy to northeast of Vladivostok, and named by botanist differentiate it from spreading jumpers, whose V. L. Komarov in 1923. branch tips tend to flare upward Despite being discovered and named over 80 The individual branchlets of Microbiota years ago, Microbiota decussata is often described decussata are arranged in lacy, fernlike sprays, in garden catalogs as "new" or "recently discov- much like those of arborvitae; no doubt this ered." This claim is actually not so far off, since accounts for another common name for the there was a significant lag between the plant’s plant, "Russian arborvitae." The branchlets are discovery and its introduction to gardeners in covered with closely pressed, scale-like needles North America. The species was not mentioned arranged in opposite pairs. The pairs emerge at in Hortus Third, the 1976 edition of the vener- 90-degree angles from each other, resulting in a able tome that lists cultivated plants of the U.S. neatly layered, four-ranked arrangement termed and Canada. It has slowly become more available decussate-hence the plant’s specific epithet in the nursery trade over the past 20 years, how- decussata. The individual needles are tiny (one- ever, and is clearly now here to stay. eighth inch or less), with convex outer surfaces, Microbiota decussata is the lone species in its a triangular shape, and tips that feel slightly , but it is not without relatives. It belongs sharp when you run a finger down the branchlet to the family, a wide-ranging group of backwards, from tip to base. coniferous trees and that includes well- The foliage can safely be described as a pleas- known evergreen genera like Jumperus, Thu~a ant bright green during the growing season but (arborvitae), and (false cypress). describing its winter color is a highly subjec- Taxonomically, M. decussata is perhaps most tive exercise. Those who don’t like the plant similar to orientahs (oriental use terms like "dull brown" or "dirty purplish 16

of organic mulch-wood chips, shredded bark, or pine needles- applied in a wide circle around the plant will help keep the root zone cool and moist. So far M. decus- sata has not shown susceptibility to Phomopsis tip blight, a com- mon disease problem for some of the spreading junipers, and appears to be free of other major disease or insect problems. When Microbiota decussata started to become available in nurseries it was often touted as extremely shade tolerant. This was seen as a great advantage over spreading junipers, which grow poorly and exhibit thinning foliage Microbiota decussata has a natural affimty for rocks in shade. More experience with brown" while those who find it appealing M. decussata has led to modified recommenda- describe the color as anything from "magnificent tions, however. It too is prone to limited growth " copper" to "rich bronze" or "burgundy purple." and thinner foliage when grown m dense, full Beauty (and color descriptions) are clearly in the shade, so the better choice seems to be partial eye of the beholder. Plants grown where they shade or full sun exposure. In regions with hot are shaded during the winter show less bronzing summers this Siberian native appears to benefit than those in full sun. Some plants seem to green from partial shade, especially in the afternoon. up more quickly than others in the spring; per- Microbiota decussata is usually sold in con- haps in the future nursery growers should select tainers at nurseries and garden centers, but for this trait in new cultivars. is also available from a number of mail order Being a conifer, Microbiota decussata does of garden catalogs. While it can be grown from course bear cones, but they are so small as to be , most commercial propagation is by rooted hardly noticeable. Male and female cones occur stem cuttings. on the same plant-in other words, it is monoe- This is a plant with multiple uses in the land- cious. The male cones are the smaller, about scape. Because of its low height and wide spread, one-sixteenth to one-eighth inch long; they it makes an ideal evergreen groundcover, its ferny, release pollen in the spring. Female cones, about layered foliage creating a three-dimensional that is in It one-eighth inch long, consist of a single naked effect lacking many groundcovers. seed held within two to four leathery scales; the has a natural affinity for rocks, whether sweep- a decorative mature in late summer or early autumn. ing around the base of well-placed or over the of a stone retam- It is a very cold hardy plant, surviving through boulder spilling top wall. Attractive it also combines well USDA zone 3 (average annual minimum temper- ing alone, ature minus 30 degrees to minus 40 degrees F). In with small deciduous shrubs, herbaceous peren- and other . Even its bronze winter fact, it seems to prefer cooler climates and may nials, fail to thrive in areas warmer than USDA zone color shows to advantage when contrasted with the dark of the colorful 6. Excellent soil drainage is a must, but as long green foliage evergreens, fruit of shrubs like Ilex verticillata ’Red as the site is well drained the plant can adapt Sprite’, or the tones of ornamental to a range of soil types and pH levels. It grows light grasses. well in evenly moist soil, but once established it also tolerates drier conditions. An inch or two For a note about the author, see page 25.