A meeting with Cladrastis

Many years ago I visited Westonbirt Arboretum in Gloucestershire, UK, to enjoy the annual spectacle of their autumn colour. Westonbirt is a huge place; to really experience the place properly you need to spend a good couple of days there! Most people gravitate to the ‘Old Arboretum’, where the biggest trees are found.

I remember my first trip to the Old Arboretum; it was very busy but the trees were magnificent so I didn’t care! The collection at Westonbirt is superb and well cared for, and I remember the vivid reds, yellows and oranges against the clear blue sky. One of the trees that stood out in my mind was a vast column of golden yellow, which turned out to be Cladrastis kentukea, the ‘Kentucky Coffee Tree’.

I’d never come across the genus before, let alone the species. I did a bit of research, but nothing really very in-depth. Thus, for many years now I’ve been under the impression that Cladrastis are rare in my area because they prefer a more ‘continental’ climate, rather than the ‘maritime’ climate of my region. I also believed that this is a mainly American genus. It’s funny how easy it is to get the wrong impression!

2019 was a turning point for me when it comes to the genus. I find that in many cases a specific encounter with a plant triggers a deeper appreciation for a genus, and with Cladrastis this encounter came in the July of 2019 on a trip to Killerton, a National Trust owned property near Exeter, Devon, UK. While exploring the interesting collection of woody species in this historic garden I found myself walking along a footpath at the very edge of the garden, far from the house and the more popular formal garden. As the path took a sudden turn and went steeply down hill I found myself under a small tree covered in heads of tiny pale pink flowers. The effect was magnificent, and initially I just stood and admired the tree, enjoying the low hum of the various species of bee that were feeding on the flowers.

My mystery tree, bathed in sunlight

One look at the flowers revealed that this tree was a member of the Fabaceae, or ‘pea family’, but apart from that I was clueless. For a plant enthusiast like me there is little more annoying than finding a new mystery plant with no label, so I was greatly relieved to find a label without too much trouble; Cladrastis sinensis.

In a flash I was taken back to my encounter with C. kentukea all those years ago. This encounter also questioned the assumptions that I had made about the genus and what it wanted. Firstly this tree was most definitely not American, and secondly there is no way that Exeter has a ‘continental’ climate! Granted, Exeter has a climate noticeably drier than my area, but in terms of temperatures we’re only maybe one or two USDA zones apart; I’m z8(a), Exeter is probably comfortably in z7.

Cladrastis sinensis

W.J. Bean wrote that this tree was initially discovered by Pratt in 1890 during an expedition to Szechuan Province in China, but was then discovered in Yunnan Province by Forrest and Henry, and was introduced from Hubei Province by Wilson in 1901. As is often the case, Bean describes a plant as perfectly as is possible: “It is not so commonly planted as it deserves to be, for it makes an elegant small tree and is one of the few that blossom in high summer.” Certainly the Killerton tree was very elegant, and based on my encounter I would also have to agree that it needs to be planted more widely.

My first encounter was with Cladrastis kentukea in its autumn colours, and I’ve come across smaller trees this autumn at Westonbirt and at the RHS Garden at Wisley in Surrey, UK. In both the Silk Wood (‘New Arboretum’) at Westonbirt and in the garden at Wisley this species made attractive rounded trees, maybe 10m (30ft) tall and wide. It was interesting to see how the more exposed leaves on the tree had turned golden yellow while the more protected leaves were still green!

C. kentukea is native to the south eastern parts of the USA, particularly in Tennessee but isn’t exactly ‘common’ anywhere. It’s rare for it to flower, at least prolifically, in the UK; this is probably why I’ve assumed that the whole genus needs the hot summers of a continental climate! In the UK at least, this is primarily a tree grown for its autumn colours which, as you can see from the pictures above, are rather excellent! This is potentially a fairly large tree, and the fact that it’s only really a tree for autumn might give a clue as to why it’s not more widely grown.

Whether or not it will grow in the cooler and wetter areas of the UK I do not know, but now that I am a little more aware of this genus and its potential I think I will look forward to seeing more Cladrastis in collections. Certainly in July I will be looking out for the Chinese and Japanese species, which are more likely to be in flower.