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Plant Profiles

Columnar Incense Cedar

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The foliage of many evergreens isn't, literally, evergreen. When the weather turns cold, it darkens. Its leaves become suffused with tan, yellow, burgundy, or even red. Plants whose ever-present foliage also keeps a good quality green are at a premium.

 

The green of the foliage of "incense" cedar is so faithful that I think the common name should be "green" cedar. We might not be out in the garden every day of the Winter to enjoy its fragrance, but we see the garden (even if just from the house) every day of the year. When it's cold, visuals trump olfactories.

 

This form of Calocedrus decurrens, 'Pioneer Sentry', has yet another talent. Its columnar shape is so narrow it can rival the "pencil" cedars that grow all over Italy and California. But Cupressus sempervirens 'Stricta' isn't hardy north of Virginia—and would still need to be tied together from top to toe if it weren't to be destroyed by a single heavy snow.

 

calocedrus-decurrens-pioneer-sentry-wider-011613-640

 

My 'Pioneer Sentry' is still young: It's only seven feet tall and could mature at over forty. So far, it has shown no sign of developing multiple trunks, which can make incense cedar trees splay open with heavy snow and, alas, not close back up when the snow goes. Yes, its habit is still loose and open. All forms of Calocedrus accept pruning; with an annual trim in early Spring, I hope to "dense up" my 'Pioneer Sentry' dramatically.

 

Here's how to grow this unusually narrow, and truly evergreen, conifer:

 

Latin name

Calocedrus decurrens

Common name

Incense cedar

Family

Cupressaceae, the Cypress family.

What kind of plant is it

Evergreen conifer.

Hardiness

Zones 5 to 8.

Habit

Strongly upright and narrow: mature specimens can be more than ten times as tall as they are wide. But, judging from mine, the trees are open and gangly as youths.

Rate of growth

Medium.

Size in ten years

Growth rate depends on climate and habitat. Faster in milder and wetter climates. In New England, a one-gallon starter plant, which might be under two feet tall, could be expected to grow from six to eight feet taller in a decade. In a milder climate, it might grow half again as high. Ultimately to about forty feet tall but only three feet wide. 

Texture

The feathery foliage is so similar to that of arborvitae that most garden visitors can't tell the difference.

Grown for

its foliage: Soft, with the "fanspray" growth habit of the foliage of arborvitae. Here in New England, incense cedar and Hollywood juniper, Juniperus chinensis 'Torulosa', usually have the liveliest cold-season hue of green of any of the ever-"green" conifers, whose green can, by comparison, become muted or bronzed when temperatures are below freezing. When brushed, the foliage releases a "fresh from the mountains" scent, hence the common name of incense cedar.

 

its habit: Columnar conifers are always of interest, particularly in climates colder than Zone 7, where the gold standard of columnar conifers, Italian cypress, Cupressus sempervirens 'Stricta', is not hardy.

 

its tolerance of heat and drought: As evidenced by plants thriving in Georgia as well as Nevada, Calocedrus thrives in hot climates, whether they are low- or high-humidity.

Flowering season

Summer. There are male and female inflorescences. The males are small, yellow, pointed, and profuse. They are formed at the very tips of the branches. They're too small to be showy at anything other than close-range and, so, are all the more intriguing when cut for use in arrangements. The female inflorescences, not showy in themselves, mature to small cones that, alas, are also not showy.

Color combinations

The foliage derives its green "warmth" from a healthy dose of yellow, making Calocedrus a natural amid white, yellow, orange, red, and burgundy.

Partner plants

Plants with a dramatic shape—columnar in the case of 'Pioneer Sentry'—could be combined on the basis of shape alone, because they provide such a strong single characteristic to respond to: A lone 'Pioneer Sentry' arising from a sweep of a comparatively low groundcover, such as the broadleaved evergreen shrub Prunus laurocerasus 'Zabeliana' or the deciduous stoloniferous groundcover Xanthorhiza simplicissima. A group of 'Pioneer Sentry' as a Greek chorus standing ankle-deep in pachysandra, or shin-deep in winter jasmine. A line of 'Pioneer Sentry', spaced twenty feet apart down a long drive.

 

Because columnar trees and shrubs make such a strong point, literally, of beginning (at the ground) and ending (at their tip), a striking choice could be to omit immediate companion horticulture. There's plenty of story to tell with just geometry. Plant a grove of 'Pioneer Sentry' in a large oval of gravel, or in generous planting pockets in a large terrace. Make it all mysterious and, therefore, even more enticing, by surrounding with a high hedge.

 

Incense cedars have showy-enough trunks that they deserve to be grown without being accessorized with self-clinging vines and shrubs (ivy, euonymous, crossvine) or scandent swaggers (rambler roses, winter jasmine, bamboo-leaved raspberry). This is particularly true with 'Pioneer Sentry', whose narrow canopy is so much more at risk for being shaded by the growth of such partners. At the most, grow ivy up the trunk only to a certain height; clip off any stems that would explore higher. Is the ivy allowed to climb just a foot or two? Then the trunk is wearing an ivy "spat." Three or four feet? "Leggings."   

Where to use it in your garden

With formative pruning to help the foliage grow more densely, 'Pioneer Sentry' would make a narrow hedge, and would also be a living exclamation point when planted singly or in groups. (A group of cattle is a herd, and a group of fish is a school. What is a group of exclamation points?) 

Culture

Sun in almost any well-draining soil. Calocedrus isn't picky, but fastest growth occurs in moisture-retentive and nutrient-rich soils.

How to handle it: The Basics

In Zone 6 and 7a, plant in Spring only. In Zone 7b and warmer, plant in Spring or Fall; water enough in the first year to facilitate establishment. Unless you're pruning as a hedge, where density and uniform height are the goal, plants usually need little attention after establishment.

 

Plant two feet apart to grow into a hedge. To ensure uniform growth, provide uniform exposure to full sun over the length of the hedge, as well as a planting bed of uniform depth, drainage, moistness, and soil richness. Prune in late Fall or in the Winter.

How to handle it: Another option—or two?

Calocedrus often grows with multiple trunks, which can splay outward when subjected to heavy-enough snow load. It isn't practical to knock snow off of trees that are thirty feet tall and taller; consider having such large specimens cabled. Another option is to grow Calocedrus as a small-enough feature that can be "de-snowed" as needed. Like its near relative, Thuja plicata, Calocedrus tolerates pruning well. Why not grow an obelisk of Calocedrus? It which would be much rarer than any free-range specimen. Yet another solution is to cut off all but the main trunk; additional trunks usually arise from very low, either from the main trunk or almost at ground level.

 

The unusual narrowness of 'Pioneer Sentry' is an advantage in that it lessens the leverage that snow-load can place on the branches. But as anyone who has ever grown 'Skyrocket' juniper knows all too well, even the narrowest conifers can be broken apart by heavy snow. My plants of 'Pioneer Sentry' are still young, and have not revealed whether this cultivar has a tendency to multiple trunks. Here's hoping not. To my knowledge, this tendency isn't mentioned in "the literature," print or on-line.

Any (other) quirks or special cases?

Individuals of Calocedrus decurrens usually adopt a narrower and more columnar habit when growing in climates with comparatively cool Summers, such as those in Great Britain or the Pacific Northwest. In hot-Summer climates in, say, California or eastern North America, the trees develop their normal width, which is comparable to that of Thuja plicata and Cryptomeria japonica. It isn't known how climate affects this difference in width. Calocedrus cultivars with narrow habit, such as 'Pioneer Sentry' and 'Columnaris', are particularly welcome in these hot-Summer areas: Whatever is causing these cultivars to be narrow is overriding the hot climate's width-widening effect.

Downsides

Deer will browse any accessible foliage; protect young plants until they have grown higher than deer typically care to reach. Seven feet is usually high enough. Even then, the result will be a bare trunk topped by a full-foliaged growth. This can be quite handsome—and also provides opportunity to add "spats" or "leggings" of a contrasting self-clinger. If full-to-the-ground foliage is your goal, Calocedrus will need to be grown in a deer-free environment.

 

Be alert for development of multiple trunks; either cable them together or remove all but the single most vigorous one.

Variants

There are a few species of Calocedrus native to southeast Asia, where the wood is in high demand for use in coffins. Only C. decurrens has any presence in horticulture. 'Compacta' is wider than tall, perhaps to four or five feet in both directions. 'Columnaris' is the form usually available, whether or not labeled as such. The foliage of 'Berrima Gold' is bright yellow that becomes orange-tipped in Winter; only newer foliage of 'Maupin Glow' is gold; small patches or even entire branchlets of the foliage of 'Aureovariegata' are gold over the entire tree, for a look very similar to that of Thuja plicata 'Zebrina'. All the variegated cultivars are columnar, and all are shorter than the species.

 

Availability

On-line.

Propagation

By grafting.

Native habitat

Calocedrus decurrens is native to states and provinces along the Pacific coast, from British Columbia to Baja California. 'Pioneer Sentry' is a naturally-occurring form that appeared in Portland, Oregon.

 
 
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