A Gardening Journal

The Best Season Ever: Seven-Son Tree in "Afterbloom"

The countless white flowers of seven-son tree are showy in themselves, and are even more welcome because they lead to countless deep pink doodads that last into October. Truth to tell, these are even showier—and a heckuva lot more obscure.

 

Heptacodium miconioides mature calyces 092317 640

 

Although petal-like in their fingery length and arrangement around the center of each former blossom, these rosy-pink things weren't immediately part of the flower-that-was. One hint at their nature is in their number: there are five, whereas each flower of Heptacodium miconioides has six petals. Take a look below, especially at the flowers at the left, whose petals were still to unfurl. They are icy-green fingers, and couldn't be easier to count. Indeed, there are six of them per blossom.

 

Heptacodium miconioides flowers closer 091117 640

 

Notice how confusing it is that, with five rosy-pink things and six petals, this tree's common name of seven-son tree is still unclear. See the prior post on this tree when it was in full flower, for the explanation of just what about it occurs in groups of sevens.  

 

Below is an even closer shot of other young flowers. You can just barely discern a short point of green between the bases of petals in the center-left blossom. 

 

Heptacodium miconioides flowers really tight showing young calyx 091117 640

 

After the white petals drop off, these little green points are what will lengthen enormously—well, in comparison—and turn the showy rosy-pink you see below.

 

Heptacodium miconioides mature calyces 092317 closer 640

 

In the picture below, these rosy structures are much smaller than those in the pictures above. No surprise: theirs were the very last of the tree's flowers to form.  Weather permitting, these rosy-pink doodads will mature to the size of the rest.

 

Heptacodium miconioides emerging calyces 092317 640

 

But what are they? Structures such as these, which originate in back of the petals and, typically, are more rigid than they, are sometimes called sepals. Some references for Heptacodium refer to them as another at-the-base-of-the-flower supporting structure, a calyx. Whatever term you use, it's not unusual for this base-of-the-blossom structure to enlarge and increase in coloring after the flowers' petals have fallen and seeds have been formed. Sometimes after fertilization, the plant's ovary swells into a large, moist, fleshy structure better known as a fruit. In these cases, the sepals or calyx might scarcely be in evidence. Take the apple: the fruit itself is gigantically prominent, whereas the calyx is just the tight group of little pointy papery bits at the center of the bottom.

 

But with seven-son flower, the small capsule below the calyx is all the fruit that will be formed. So the rosy calyx becomes showy by default.

 

Heptacodium miconioides merging calyces 092317 B 640

 

This display is powerful even at a distance. Below is one of the oldest and largest specimens of heptacodium that I know of, on the grounds of this nursery in Connecticut.  

 

Heptacodium miconioides Broken Arrow overall 100817 C 640

 

This magnificent tree is perhaps twenty-five feet tall and fifteen feet wide. Scores of flower clusters as big as those of mophead hydrangeas bedeck the branches. Now that they have matured to rosy-pink calyces, the show is more brilliant than ever.

 

 

Here's how to grow this must-have tree:

 

 

Latin Name:

Heptacodium miconioides

Common Name:

Heptacodium, seven-son flower. I prefer seven-son tree, because "flower" could be interpreted as meaning that this species is herbaceous.

Family:

Caprifoliaceae, the Honeysuckle family.

What Kind of Plant Is It?

Hardy deciduous tree.

Hardiness:

Zones 5 to 8.

Habit:

Upright, irregular, multi-trunked, and open. The result could be seen as artistic—but, if not, heptacodium responds enthusiastically to pruning. See the second "How to Handle it" box, below.

Rate of Growth:

Medium to fast.

Size in Ten Years:

Twenty to twenty-five feet high, and half to three-quarters of that height wide. The ultimate mature size could be larger; the species is comparatively new to Western horticulture: See "Native habitat," below.

Texture:

Open throughout the canopy, usually with lower limbs and trunks fully exposed. This is to the good, in that the trunks' exfoliating bark is a show in itself. 

Grown for:

Its rarity in gardens: Heptacodium began to be widely known in Western horticulture only in the 1980's, thanks to the Arnold Arboretum. For more of the story, see "Native Habitat," below.

 

Its flowers: Tiered clusters of white flowers emerge in late summer; they are so sweetly scented that this species was originally named Heptacodium jasminoides. Although this tree isn't botanically related to the Jasminum family, marketing-wise this was a much more engaging species name than H. miconioides. Ah, well. In the larger flower clusters, there can be six tiers of bloom, with a solo flower—the "seventh son"—at the tip of them all.

 

Its calyces: After the flower petals fall, the calyces enlarge and turn cherry red. This display is even more striking than the flowers.

 

Its toughness: Heptacodium tolerates salt spray, is drought tolerant when growing in soil of normal moisture-retentiveness, and is hardy in climates as cold as Zone 5.  

 

Its lack of appeal to browsers: Heptacodium is not reported as being at risk.

 

Its flexibility of handling: Heptacodium is usually grown as a full-size free-range tree, but could also be trained as a formal standard, an informally-pruned large shrub, a radically-pruned coppice, or a grove—pruned as above, or free-range—of trunk-like root sprouts.

Flowering & "Calyxing" Seasons:

Late Summer: Here in southern New England, buds begin to mature to flowers in August, but the floral display doesn't peak until September. The show of rosy-pink calyces to follow extends well into October.

Color Combinations:

The white flowers of heptacodium go with everything. Although their follow-on display of rosy-pink calyces is both prominent and enjoyable, this doesn't limit heptacodium to just pink-friendly settings. The diversity of fall foliage—plus the all-too-soon months of winter that follow, when color in the garden is dramatically scarce—make fall a free-for-all for color. With few exceptions, the garden in winter is an essay in dark greens and brown or tan bark so, in fall, let the garden live it up.

 

The brown, tan, and parchment colors of a heptacodium trunk with full-on exfoliating bark go with everything, and are more or less on display year-round. The bark is so striking that the tree could partner thrillingly with plants celebrating copper, ebony, cinnamon, tan, and parchment.

 

See "Plant partners," below. 

Plant Partners:

Heptacodium's diversity of training possibilities means a diversity of contexts and companion plants: If the tree is free-range, for example, it can function as a shade tree, with shade-loving underplantings. If grown as a pollard, coppice, or hedge, it will normally be in full sun, and will be surrounded by sun-lovers. Here are suggestions for all the contexts:

 

 

When heptacodium is a full-size, free-range ornamental tree, its flowers and calyces are showy in themselves, so the tree doesn't need special attention of, say, even larger dark-green trees that provide contrasting backdrop. Instead, partner-plant opportunities are for beauties that either appreciate the dappled shade the heptacodium creates spring into fall, or are at their peak in fall and winter, when the heptacodium is leafless, the sun (such as it is) is full, and the tree's striking tan-and-parchment bark is most prominent.

 

Ensure a solid baseline of interest year-round by including some "dapple-tolerant" evergreens; choose those whose foliage is, variously, small, rounded, jagged-edged, feathery, or needly, to contrast with the comparatively large pointed heptacodium leaves. If at the front, shortness is key so that the heptacodium's stunning trunk isn't hidden. What about Cephalotaxus harringtonia 'Prostrata'Sarcococca humilis, or Liriope spicata? (If you're lucky enough to be gardening in Zones 7 and 8, also consider Aspidistra elatior.) At the sides and back, heights of three to six feet aren't likely to interfere with your view of the heptacodium's typically multi-trunked or low-limbed architecture. What about Mahonia bealei and Taxus baccata 'Amersfoort'?

 

Shade-garden seasonals to add for the warm months include Hydrangea quercifolia, especially in its comparatively compact forms, 'Pee Wee' and 'Sikes Dwarf'. The foliar contrast between it and the heptacodium is sensational; the dusky pink of the hydrangea's maturing flower clusters might pair well with the heptacodium's calyces but, even so, it's more of a bonus compared to the season-long foliage that this shrub provides. Azaleas are another option, but more for their shade tolerance, mounding habit, and small round foliage that their blooms. These occur long before the heptacodium calyces are colorful, so could be of any color. Eleutherococcus sieboldiana 'Variegata' is another shade-happy stalwart. The five-lobed foliage is contrasting in itself, but the best forms have variegation that is downright luminous in its creamy intensity. Cut this shrub to the ground every other year to keep it in bound. Xanthorhiza simplicissima is another option for great foliage contrast, this time in texture and form, not color.

 

 

When heptacodium's canopy is pruned as a coppice, pollard, or hedge, it and the tree overall are both relatively compact. The heptacodium and its companions now will both be more-or-less in full sun, and its companion plants would be nearly the opposite of those above. Not least, the "tree" is now small enough that taller background evergreens would be welcome. As is always the case, small foliage and dense habit are best for backgrounders, with Taxus and Arborvitae leading the charge wherever heptacodium is hardy.

 

With the heptacodium's blossoms and calyces now more or less at human-height, partners that might also be cherry-pink in early fall could be considered. But it's a tricky business. Would PG and oakleaf hydrangeas, lespedezas, and tree viburnums look repetitive, in that their pink-in-late-summer displays are also comprised of countless small flowers arrayed in large heads? Alas, the unique metallic-lavender fall berries of callicarpa are clashing instead of complementary.

 

Other pink-friendly options including a pink-fruited crab-apple planted in the background, such as 'Pink Glow'. Gardeners in Zone 7 and 8 could choose among pink fall-flowering camellias. Ornamental grasses for the sunniest side of any heptacodium include those with pink-friendly plumes, such as Miscanthus sinensis 'Huron Sunrise' and Panicum virgatum 'Shenandoah'. 

 

To my surprise, one of the best full-sun partners for heptacodium is Baccharis halimifolia. Yes, its fall display is also thanks to large heads of countless small flowers. But instead of being predominantly pink, they are white with only small flashes of pink. The pairing works!

 

 

When heptacodium is planted as a grove, whether from a multi-trunked and root-sprouting soloist, or en masse as an "orchard," the collective power of the trunks' exfoliating bark synergizes with the aggregate irregularies of the trunks' confirmations to brush aside any thoughts of underplantings that are anything other than low, uniform, and deferential. Any one of these would be superb: Liriope spicata, massed Cephalotaxus h. 'Prostrata', Xanthorhiza, and Buxus sempervirens 'Tide Hill'.

Where to Use It in Your Garden:

Heptacodium's seasonal displays from late summer to fall merit close inspection, as does the dramatic striping on the trunk (showy year-round) created by the exfoliating bark. So, rather than adhering to recommendations for spring and summer palettes—that pink not be associated with red or orange—site the tree anywhere that enhances intimate viewing, regardless of whether colors of nearby plants might clash. 

 

Because the tree naturally shapes itself into a small-to-medium-sized multi-trunked specimen, it could function as the tree in a small sunny courtyard. In this usage, it would be a welcome break from what may well be the de rigeur first choice, a cultivar of Japanese maple.

 

Because the floral and "calyxial" shows are produced at the tips of new wood—whether originating at the top of older wood, or springing directly from the base of the trunk or even the roots—heptacodium lends itself to some radical pruning strategies that enable what would otherwise be a twenty-five-foot tree to thrive as a five- to twelve-foot shrub or standard. This would enable it to mix harmoniously with perennials, shrubs, tropicals, and ornamental grasses in a mixed border. Besides individual filler in such a mixed planting, heptacodiums that are cut back severely each spring can be planted en masse. If many are planted in a line, the result would be a summer-into-fall flowering (and calycing) hedge. If planted in a block, cut-back heptacodiums could be a component of formal planting schemes, filling sharp-edged beds fronting a hotel, or a civic or corporate institution.

 

The artistically irregular form of free-range specimens, plus the reported tendency of older trees to send out root sprouts, suggests that heptacodium could form a grove, where it would automatically be the focal star of a space of almost any size. On an even larger scale, multiples of heptacodiums could form an allée or, in a carefully-sited platoon out in a large meadow, an "orchard."

 

See "Plant partners," above, plus the second "How to handle it" box, below.

Culture:

Plant in soil with average to good moisture retention.  In Zones 6 and 5, Heptacodium miconioides usually does best with all possible sun and heat. Even so, the tree isn't notably drought tolerant, especially in soil that doesn't provide normal moisture retention. A drought-stressed heptacodium is likely to display black-edged foliage by high summer.  

 

In Zones 7 and 8, this tree is an easier keeper when it receives a bit of shade from hot mid-day and afternoon sun.

 

See "Where to use it" and "Plant partners," above.

How to Handle It: The Basics:

Plant in either spring or fall, ensuring enough water for establishment. In normal garden soil and settings—see "Culture," "Where to us it," and "Plant partners," above—heptacodium needs no supplemental watering.

 

As a free-range tree, formative pruning usually isn't necessary: The tree naturally develops multiple trunks, plus a relatively high and open canopy, which combine to display the lower portions of the thicker stems' artsy irregularities and peeling bark to perfection. Unlike, say, Stewartia or (especially) Clethra barbinervisboth of which benefit from sensitive pruning-away of some (or many) lower branches so that the gloriously-barked lower trunks are in full reveal whether in foliage spring through fall, or bare in winter—heptacodium stems typically produce most of their foliage on first-year stems: The following year's new growth, then, begins to bear leaves a foot above the now-bare older stems. Then, as it grows, additional leaves are two, three, or four feet higher still. The result is that there usually aren't older stems that, having become shaded out by newer growth, have died and need to be cut out. They never formed in the first place. Talk about easy!

 

In Zone 5 or even in a nasty winter in Zone 6, some tips might die. Cut them back to leafy growth as it emerges in the spring; because flowering occurs at the tips of new stems, any such dieback (or fall-through-early-spring pruning that might take place for any reason) won't affect the floriferousness and "calycing" of the coming summer-into-early-fall displays. In this regard, heptacodium's reliability for floral display and—see below—pruning possibilities are both very much like those of other summer-flowering woodies such as Hydrangea paniculata, Hibiscus syriacus, Lespedeza thunbergii and japonica, and Lagerstroemia indica.

How to Handle It: Another Option—or Two? 

As introduced in "Grown For," "Where to Use It", and "Plant Partners," above, heptacodium can thrive with an impressive number of different modes of training as well as different settings, making it suitable for almost any sunny setting from a compact garden to vast park-like acreage. Each scenario requires different training.

 

To grow heptacodium as an irregular but still bushy specimen that is reliably more compact than the full-size free-ranger, in late winter or early spring cut back any branches that are out of scale. This could be a matter just of pruning away last year's stems, or could, on occasion, require getting our your folding saw to remove a larger limb. Heptacodium will normally resprout readily no matter how much or little you removed. If the setting is more compact, you may want to pinch resultant soft growth in May, which will also have the effect of creating not just a lower canopy, but a denser one, too.

 

To grow heptacodium as a standard begin with small plants, which are more likely to have just one or two straight stems, anyway. Tie whichever stem is better-aligned or longer to a permanent stake so that it matures as a vertical, then let it grow upward to the height you'd like your standard's trunk to be. Keep in mind that first-year growth that will annually reform the standard's canopy can become three or four feet long. This means that a heptacodium with just a short trunk of, say, three feet, will be a prominent six-foot creature when in flower by late August. A trunk of six or eight feet will yield a magnificent standard nine to twelve feet tall when in flower. A trunk of ten to twelve feet yields a standard that can be walked under, and is suitable for lining a walkway to create, in effect, a pergola-like canopy by high summer.

 

For any of these standards, cut away sprouts that arise from the base or from the trunk. In late winter or early spring, prune back the stems of the canopy of a young standard by at least half, so that, year by year, more and more main scaffolding branches build up. When the standard is as high and full as desired each summer, then prune these scaffolding branches back more and more severely year by year so that the canopy doesn't become larger and larger. It's likely that older standards will need most of their scaffolding branches to be cut back to a foot each year—and, every few years, all the way back to six inches.

 

If you have the energy and curiousity, experiment with pinching the new stems back by half sometime in May. Then you can determine how much this might shorten their overall extensions by the time bud formation begins in August and, therefore, mere vegetative growth that would otherwise continue to lengthen each stem would cease.

 

To grow heptacodium as a bushy and comparatively low-to-the-ground shrub that can associate well with diverse partners in a mixed border, also begin with small plants: Heptacodium grows quickly, especially when young, so there's nothing much to be gained with larger stock when your plan is to cut most of the growth off. Cut all stems back to low buds in late winter or early spring. Even with this treatment—or, rather, because of it, because such pruning removes all the growth inhibition typically produced by higher growth toward lower—new stems could grow four or even five feet high. For even more bushy and compact growth, pinch those new stems back sometime in May. See if pinching more severely delays flowering too much, or if pinching just the soft tips of the growth makes more but smaller heads of flowers (which may or may not be desirable).

 

Growing heptacodium en masse as either an informal summer-flowering hedge or a summer-flowering block of woody growth requires roughly the same handling as for an individual cut-back specimen. As with that, experiment how cutting stems back more or less—let alone pinching the resultant growth more or less, later or earlier—affects the height and density of growth that is allowed to mature to flowering, as well as the potential delay in the start of that flowering.

 

Spacing for these options varies considerably. For planting in blocks, space young shrubs four or five feet apart. For a summer hedge, space two to three feet apart.

 

To ensure that heptacodium has more trunks, or more branches that emerge lower down, cut young starter plants down to lowest buds in late winter or early spring for several years after planting. As the shrub matures, you may find that it will also begin producing shoots directly from its roots in response. Then's the time to let all the stems mature as free-range growth, with the result being a dense stand of colorfully barked trunks: a "hyper-grove," if you will.

 

For a grove with trunks that are less densely spaced, plant heptacodium in groups of three or more. Even when mature, a heptacodium canopy isn't likely to be more than fifteen to twenty feet in diameter, so you can plant trees ten to twelve feet apart without worrying that you'll be crowding them.

 

For maximal command of larger spaces—a grove out in a meadow, say, or an allée of heptacodiums along a walkway or drive—space the trees fifteen to twenty feet apart so that each individual's canopy will receive enough sun all around to  luxuriate laterally not just vertically.

Quirks and Special Cases:

There are reports that stems can emerge directly from the roots, which would transform a single tree into a many-stemmed colony. I don't have direct experience with this among the heptacodiums I've planted over many years but, because this tree's trunks display such attractive exfoliating bark, appearance of additional stems might just enhance that show. It's likely that the vigorous pruning options explored in the second "How to handle it" box, above, would encourage emergence of these root sprouts. (Cut them off at ground level if they don't fit in with how you're training your heptacodium.) See that box, also, for suggestions on their use as an additional aspect of this species' seasonal display.

Downsides:

Foliage of Heptacodium miconioides doesn't develop showy colors in the fall. A watery yellow-green is about the best you can expect. This is a minor failure in comparison to the extraordinary summer-to-early-fall display of flowers and calyces.

Variants:

Seed-grown progeny show sufficient variance in the rosiness of their calyces that cultivars are beginning to be named on that basis. Those of 'Red Select' are more deeply colorful; purchase it from this peerless nursery. To my knowledge, forms that vary in flower size or color, bark exfoliation, or overall size and habit haven't yet been identified.

Availability:

Online and, increasingly, at regular garden retailers. Hooray!

Propagation:

By seed and by cuttings.

Native Habitat:

Heptacodium miconioides is native to central China. It was first discovered in 1907 by the legendary British plant explorer and collector Ernest "Chinese" Wilson, who introduced about two thousand Asian plant species to the West. About sixty bear his name. Apparently, heptacodium wasn't successfully introduced to the West by Wilson; it took another botanizing trip in 1980 to yield viable seeds. These were sent to the Arnold Arboretum, which germinated them and then—at last!—re-introduced this species to the West.

 

Heptacodium is now grown world-wide. 

 
 
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