Microbiota decussata

Several years ago, on a visit to the Rhododendron Species Botanical Garden in Federal Way, Wash., I encountered a low-growing evergreen shrub labelled Microbiota decussata. At first glance I mistook it for its genetic cousin, the juniper, but its soft, elegant texture made me quickly realize that this was something special. In fact, Microbiota decussata is the lone species in its genus, belonging to the same family, Cupressaceae, as its more flamboyant relatives the Thuja, Chamaecyparis and Cupressus. It’s road into cultivation and specifically into American gardens has been a slow process.

The species was first recorded by botanist I. K. Shishkin in 1921 when he found it growing in its remote native range in far-eastern Siberia, bordering on the Sea of Japan. Its discovery, like all discoveries in the newly formed Soviet Union, was considered a “state secret” and it was over 50 years later that restrictions relaxed enough for the plant to be shared with the western world. I’m imagining a Russian botanist during the cold war telling his western colleague, “I’d like to send you this beautiful plant, but then I’d have to kill you.”

Microbiota is hardy to USDA Zone 2 and grows well in full sun to partial shade. It is a low, spreading evergreen groundcover, attaining a mature height of 12 to 24 inches. The foliage is a beautiful bright green during the growing season and fades to a rich bronze-purple in winter. It must have excellent soil drainage and will adapt to regular, even watering or is drought tolerant once established.

In nursery production, it’s critical that Microbiota is grown in a well-drained soil mix or it will be prone to root diseases. Some growers have discovered that it can easily be grafted onto Thuja occidentalis to create a lovely tree form of the plant that makes a stunning addition to the landscape or a beautiful evergreen container specimen. I had a great conversation about Microbiota with Doug Wilson, the curator and caretaker of the conifer plantings at the Oregon Garden. He lauds the merits of this plant and believes that the grafted form is much more desirable than growing it on its own roots.

“It can be grown on its own root system, but you have to be very careful about watering and soil mix, as it is prone to root diseases if it’s too wet,” Wilson says.

Microbiota received the Cary Award in 1998, an awards program that annually honors outstanding woody plants in New England gardens. It is also a selection by Great Plant Picks, which is a comprehensive list of hardy, reliable plants for home gardeners and industry professionals focused on the maritime Pacific Northwest.