To paraphrase the Tenacious D song, “This is the greatest and best tree in the world”.
Despite over 100 years passing since Ernest Wilson discovered this species growing in the Chinese proving of Jhejiang, Heptacodium miconioides still suffers from woeful obscurity, despite being possibly one of the most useful and downright awesome late flowering shrubs. I’m interchanging ‘tree’ and ‘shrub’ here because while Heptacodium is technically a shrub (by the definition used by Grimshaw & Bayton 2009) it grows pretty big and will, I would expect, be regarded by most gardeners as a multi-stemmed tree. It is regarded as rare in the wild, and it was really only a 1980 expedition that provided momentum for this species to reach cultivation.
It’s possible that the obscurity of H. miconioides might be down to its name; while initially intimidating, once you’ve got the hang of ‘hepta-codium mico-nee-oides’ it’s not that much of a tongue twister, and is a lot less cumbersome than the common name of ‘Seven Son Flower Of Zhejiang’. If you can pronounce ‘Zhejiang’ then ‘Heptacodium’ should be a walk in the park! Another reason for the relative obscurity of this species is that it is not an easy plant for a nursery. Firstly, as a young plant in a pot this species has a sort of awkwardness about it, where it grows into any shape except one that is pleasing to the more casual gardener, and secondly this species puts out long new shoots that are rather brittle and will bring down the wrath of the ever moaning gardeners if the plant gets damaged in transit.
Once the hurdles of acquisition have been overcome, Heptacodium miconioides is happy in all but the extremes of wet and dry conditions, and prefers a neutral, humus-rich soil. Once it is established it seems fine in exceptional heat (like that of summer 2018 in the UK) and has a hardiness rating of USDA z5, which would certainly make it hardy across the British Isles.
Heptacodium miconioides is a very distinctive plant, with large, pointed green leaves that hang along its branches a bit like bat wings, if you are prone to flights of fancy. It’s a fairly fast growing species, becoming a sizeable shrub 2-3 years after planting a <1m specimen (subject to good care). Best of all are the flowers and the bark.
Not many woody plants come into flower in September! While individual flowers are fairly small, the collective mass of flowers on an established plant are best described as a ‘cloud’, but Heptacodium miconioides has another trick up its sleeve to delight gardeners; once the white flowers have dropped the red calyx stays intact, essentially giving the plant a flush of white followed by a flush of red! This trick is a bonus of Abelia and its relatives (although Heptacodium seems to be heading for a closer affinity with Lonicera), although Abelias flower much earlier in the year. While I’m confident that I once got a light scent from this species I don’t think it’s reliable or strong enough to really call Heptacodium flowers ‘scented’. There have been observations that this species is an excellent late food source for many species of bees and butterflies. British gardeners, who are fixated by the belief that only native wildflowers have any wildlife value, can disregard this as nonsense, but I include this for the benefit of those gardeners from other areas who want to provide valuable food for insects for as much of the season as possible.
The other big draw of Heptacodium miconioides is its bark. This is not a bark for those who are easily amused by the white bark of certain Betulas or the red of Prunus serrula; no, the beauty of Heptacodium bark will only be appreciated by gardeners of discerning taste. It’s not easy to describe the bark in any way that sounds even remotely appealing; it’s a light grey-brown, with thin peeling strips, and yet to a ‘barkophile’ it has a quiet charm.
The autumn colour of Heptacodium miconioides isn’t really in the top ranks when compared with the green-leaved Acers, Nyssa or any of the other greats. To be honest it’s never really caught my attention, although from memory I think it was golden yellow. Maybe away from the gentle climate of Devon and Cornwall (mild, maritime UK) it makes a greater impact?
And so we come to the question of ultimate size in cultivation. This will be a challenge, not least of all because most, if not all, of the big trees in cultivation in the US, Britain and mainland Europe are from the 1980s so it’s probably fair to say that they haven’t had long enough to grow to their full potential. In his excellent ‘Tree Of The Year’ article for the International Dendrology Society (currently available on their website), John Grimshaw notes that climate can have quite a strong effect on the rate of growth; the largest plant at the Hillier Arboretum has reached 8m tall since 1981, while plants introduced to the cooler climate of Norway in the mid 1990s have reached only 3m tall (the article was written in 2012). In ‘Van Den Berk On Trees’ they give the species a height of 4-7m. From these figures it’s clear that this species isn’t exactly ‘slow’…!
Another important observation in John Grimshaw’s article is that in areas with an early start and a late finish to winter this species doesn’t always flower properly, which is an important consideration. It begs that all-important question about whether we should be looking at hardiness beyond ‘will my plant live?’ to ‘will my plant reach its full potential?’.
For US readers, Grimshaw also notes that Heptacodium miconioides has not been observed to be invasive in the US at this point, although there is obviously the fact that the species is not in widespread cultivation anywhere yet, so there might be the potential for problems in the future. To be honest I think if you’re an American gardener who has read this far, about a plant that is still fairly obscure, you’re probably sensible and committed enough to be aware of the risks in your area and to maintain due vigilance.
So in summary, this shrub/tree is fantastic! It’s big, and unlikely to appreciate attempts to keep it small, so plant it wisely so that it can grow well. It will look fantastic as a single specimen or a grove and you can, if so inclined, prune it to be a single stemmed tree. For late summer floral interest this plant has no equals, and I hope that as the message gets out there we will see this in more garden and amenity planting.