A Gardening Journal

Chinese Pearlbloom

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Chinese pearlbloom is one of the more graceful of August-flowering rareties. It bears large racemes at the tips of the new stems. They show off buff-colored buds that barely open and, so, preserve their rounded shape—hence the common name of "pearl" bloom. Thanks to the spacious array of flowers, the architecture of the raceme's branches is kept on full display.

 

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The buds start out icy green but mature to creamy white before opening. By then, their coloring has progressed to palest orange. Each bud opens just enough to reveal the flower's interior. 

 

 

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Although the young foliage is a showy burgundy in Spring, by Summer, only the burgundy of the leaf stem—its petiole—remains.

 

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Here's how to grow this easy but rare ornamental tree:

 

Latin Name

Poliothyrsis sinensis

Common Name

Chinese pearlbloom

Family

Salicaceae, the Willow family.

What kind of plant is it?

Deciduous tree.

Hardiness

Zones 6 - 7; Zone 5 with optimal siting; see "Culture," below. 

Habit

Upright and nearly as broad as tall. Unless limbed up, the trunk is short, for a habit that is as much shrubby as tree-like.  

Rate of Growth

In my experience, slow, at least in youth.

Size in ten years

After ten years, a whip might become a sapling of ten to twelve feet. The species is reported as maturing to about forty feet, and has been in Western cultivation since the early 20th Century, quite long enough for ultimate size to be attained. Even so, I'm  familiar only with mid-sized specimens of twenty feet or so. 

Texture

Dense with maturity; open in youth. The shape, size, and density of the foliage combine with the tree's habit, overall size, and cherry-like bark to create a remarkable impersonation of a tree lilac, Syringa reticulata.

Grown for

its foliage: The leaf shape is smooth-edged and cordate—meaning heart-shaped—which, in shape, size, and coloring, looks much like those of lindens as well as tree lilacs. Leaves are prominently flushed with burgundy when young—enough to qualify as a seasonal show in itself—retaining the burgundy in the petiole for the season. The foliage changes to yellow in Fall.

its mystery and obscurity: In flower, the tree looks much like a tree lilac that, unaccountably, is in flower a month later, in August instead of early July. Despite its easy-going ways, late season of flowering, and attractive Spring folage, Poliothyrsis is rare. Any shrub or tree that flowers in August and is neither a hydrangea nor a rose of Sharon would, you'd think, be much more popular.

 

its flowers: Tiny and apetalous, the flowers are profuse but widely-spaced on large, much-branched panicles that develop at the tips of new growth. The rounded buds have five sepals that open only a crack. Under magnification, their squat, basketball-in-need-of-inflating shape, and their sepals' narrow star-like opening that exposes, just barely, the flower's inner parts, is reminiscent both of bleached skeletons of sea urchins and the pillowy "plum" buns of Chinese cuisine. The buds are white, but quickly mature to the color of a creamy mix of orange and lemon sherbert. OK, "buff" is another term for the color. The flowers are reported as being fragrant; I'll confirm next year.

Flowering season

Unusually late and, hence, highly welcome: Late July into mid-August here in southern New England

Color combinations

The burgundy-flushed foliage coordinates with any of Spring's predominant colors, from the chrome yellow and orange to loud pinks and purples to the pastels and pure whites. Because new foliage emerges for several weeks—and holds its burgundy  for a while after emerging—the Spring foliage show is effective for weeks.

 

The white-then-buff flowers are tricky to incorporate with any other color than green—see "Plant partners," below—because so many of the more prevalent colors of Summer are doubtful collaborators (pinks and blues of hydrangeas) or out-and-out conflictors (strong yellows of daisies, roses, and dahlias).  

Plant partners

For two seasons, anything goes. The emergent foliage of Poliothyrsis can combine with any of Spring's colorful offerings, and (to my eye, at least) Fall is the one season when it's fine for any color to mash it up with any other. Summer and Winter are the seasons when it's worthwhile to have carefully thought through this tree's near neighbors.

 

In Winter, the leafless branches expose bark that is neutral—which is to say, boring. Perhaps the branches could be pressed into service as a scaffold for whatever evergreen climbers are hardy for you. I keep hoping that one of my variegated ivies, sited encouragingly near the tree's base, will finally discover the pleasure of climbing up its trunk. Gardeners in Zone 5 could try one of the variegated climbing euonymus; those in Zone 7 (even if just by the skin of their teeth) have abundant options, including Clematis armandii and Stauntonia hexaphylla.

 

The blossoms' Summer season is so unusual that, coupled with the species' overall rarity, planting Poliothyrsis is a guarantee that the plant will be appraised closely. And by the very folks—other plant enthusiasts—whose eyes will be the most alert for your inspired "call outs" to the creatively colorful Summer show in the immediate neighborhood. Be ready!

 

As introduced in "Color combinations," above, the flowers' coloring is at a disadvantage next to most contrasting hues, especially if they are more strongly saturated. If only there were plants whose flowers combine creamy apricot with a hue that could complement it: Blue, violet, or burgundy. Are there Summer-flowering clematis in these colors that also have pistils and stamens in the winning colors of apricot or buff? I'm not aware of any but, because clematis hybridization is always fast and furious, I live in hope.

 

Meanwhile, there are options for partners that supply colors that are collateral to buff instead of clashing: the near tones of apricot and orange. Perhaps you're gardening in a cool-Summer climate, where roses can more easily flower all season because they are spared the hot nights that usually preclude resumption of flowering until September—after which time Poliothyrsis is long out of flower. You'll need an apricot-friendly rose that is recurrent: that flowers in successive waves, not just once in May or June. And it would best be a climber, so its canes can be trained up into the Poliothyrsis branches right up to and through the tree's emerging racemes. Consider 'Lady Hillingdon' or 'Alister Stella Gray'. The flowers of 'Alchemyst' would seem to be the perfect pale apricot—but this rose, alas, is once-flowering. Even the latest of the once-flowerers are through in early July. Be sure to plant the rose so that its growth receives all possible sun even as you lead the stems up into the tree's dense canopy.  

 

Could Campsis 'Morning Calm' be grown up Poliothyrsis? Its extraordinary sprays of large pale-orange flowers should peak at the same time. Or what about placing a large container on the sunny side of the tree, and planting it with the annual climber Thunbergia alata 'Sunny Orange Wonder'?

 

The very scarcity of well-matched partners to the flowers of Poliothyrsis makes achieving a successful juxtaposition all the more sweet. It is a simpler goal, but no less satisfying one, to establish a link from the leaves' burgundy petioles to the burgundy foliage of a partner plant. There are several options to choose among, whose leaves retain a lively burgundy hue throughout the hot Summer heat. Both the leaves of Physocarpus opulifolius 'Summer Wine' and any of scores of purple-leaved cultivars of Acer palmatum provide the necessary contrast in shape and texture. 

Where to use it in your garden

Poliothyrsis is not just an oddity; it's an oddity whose seasonal shows of Spring foliage, Summer flowers, and Fall foliage are worth enjoying at close range. Site where the tree is readily accessible, so that visitors who are charmed as well as curious about the tree can easily savor its eccentricities in detail.    

Culture

Full sun and almost any soil as long as there is decent drainage. Drought tolerant, too. Reported as being easy-going, but the combination of nutrient-rich soil and decent drainage is probably the key to maximum growth. 

How to handle it: The Basics.

Plant in Spring or Fall, ensuring enough water for establishment. Doesn't require formative pruning; you can plant it and just let it do its thing year after year.    

How to handle: Another option—or two!

Because the panicles of flowers develop in mid-Summer, at the tips of the current season's growth, it should be possible to prune Poliothyrsis back in late Winter or early Spring to delay flowering still further, while also keeping the plant more compact. (In my experience, the only thing better than a shrub or tree that doesn't flower until August is one that doesn't flower until September.) Such pruning could, conceivably, maintain the habit of a shrub indefinitely. Or, if a specimen were limbed up to create a short trunk before having its top growth pruned annually, a pollard.

 

Because the burgundy flush of emerging foliage is so effective, this pruning might prolong its display as well. At the southern end of the species' range, the growing season is so long that adventurous gardeners might even try pinching the tips of soft new growth in early June, in hopes of encouraging a second flush of colorful new foliage. This would probably delay the appearance of the flowers still further. In shorter-season locations, such pinching might delay flowering until cool weather or outright frost put the kibosh on it.  

Quirks and special cases

None.

Downsides

None. Poliothyrsis is notably free from pests and diseases.

Variants

To my knowledge, no variants have yet been identified.

Availability

Occasionally on-line and at "destination" retailers, but Poliothyrsis is rarely seen anywhere.

Propagation

By cuttings and by seed.

Native habitat

Poliothrysis sinensis is native to China; "sinensis" means "Chinese."

 
 
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