Prepare to be dazzledA walk around Wakehurst at this time of year reveals a spectacular array of autumn colour, as well as the answer to an important question, as Andrew Jackson explains

‘Dad, why is this side of my apple red and the other side green?’ I find questions of this nature from my son Matthew – the ones that I cannot immediately answer – lead me on a journey of discovery that I never forget. In this case, as I began to understand the chemistry behind the apple skin question and the autumnal colours that surrounded us, my sense of beauty was enhanced by wonder.

For me, this is Kew in a microcosm – both gardens are full of beautiful, exotic, peculiar and astounding plants and fungi. Delving into the fascinating work of Kew’s scientists enhances my enjoyment and stimulates more questions and intrigue. Walking around Wakehurst in autumn after the question had been answered felt like I was seeing familiar things for the first time.

In October, as you walk from Wakehurst’s visitor centre towards the Millennium Seed Bank building, the first tree you see in bright red or even scarlet autumn colour is a red maple from the east coast of the USA. It is aptly named Acer rubrum ‘October Glory’ and has won an RHS Award of Garden Merit because of its reliable autumn colour and attractive mature shape. In the summer its leaves are green, so where is the red coming from? When we see green leaves in summer we are looking at chlorophyll – the abundant pigment, crucial for photosynthesis, that absorbs light in the blue and red spectrum, leaving us to see the green parts of the spectrum that it does not absorb. Then,

The beautiful birch tree here is Betula utilis var. jacquemontii ‘Doorenbos’. With white bark, a graceful form and bright yellow autumn foliage, it is another tree with an RHS Award of Garden Merit and is a perfect choice for smaller gardens.

To indulge yourself in the autumn spectacle of birches, remember to visit the National Collection of Betula in Bethlehem Wood. Here you’ll encounter a wide range of birches, all called Betula utilis and all from the Himalaya, but with bark varying in colour from white to dark chocolate brown. Despite the differences in their bark, they are unified in autumn colour, which is nearly always a bright clear yellow – caused by the pigment carotene.

– Andrew Jackson is director of Wakehurst

» Enjoy a guided Stroll & Soup at Wakehurst on 16 October to see the best of the autumn colour – see p71 for booking details

I N T H E G A R D E N S

as autumn commences, a decrease in light and temperature slows down the production of chlorophyll and enables us to see pigments that it has been masking, including reds, yellows and oranges.

The production of red pigments actually increases in autumn in response to higher sugar concentrations. These bright red pigments, known as anthocyanins, are responsible for the red leaves in the acer, the red skin of apples and the purple of grapes. The reaction to produce them also requires light. This is why some varieties of apples can be red on one side and green on the other. ‘Matt, the answer is simple, but fascinating – the red side was in the sun and the green side was in shade.’

Continuing your walk at Wakehurst, the next tree with stunning autumn colour that you pass on your left as you go from the red acer towards the Stables restaurant is the Chinese tupelo (Nyssa sinensis). The leaves of this species, just like its more common American relative N. sylvatica, can be red, orange and yellow. This range of colours is mainly due to carotenoid pigments – the same ones that give rise to the colours of carrots. The Chinese tupelo reaches 10–15 m tall and is much more suitable for smaller gardens than the majestic American tupelo. It is a tree I would gladly plant in my own garden.

Outside the Stables is a taster planting of Wakehurst’s four National Plant Collections – birch, southern beech (Nothofagus), Skimmia and Hypericum.

Next to the ‘Doorenbos’, outside the Stables, is perhaps my favourite tree of all. It’s a southern beech that you could easily assume was a birch, with its peeling orange- cream, papery bark. The hualo (Nothofagus glauca) is a little-known tree in cultivation and is found in the wild only in Chile. This beautiful tree is one for a large garden or arboretum. It will reach a height of 30 m, and the one in Coates Wood, planted in the early 1980s, is already 18 m tall.

This is a tree that I seek out on a weekly basis to sit by and enjoy, but also to reflect on what needs to be done to conserve this and many other threatened tree species in the wild today. It is vulnerable to extinction due to logging and the conversion of its native forests into plantations of a fast-growing western American conifer called Pinus radiata. Last year the hualo at Wakehurst was still in its autumn colour in December, almost ten weeks after the first signs of autumn from Acer rubrum ‘October Glory’.

As I walk around the woodlands of the world at Wakehurst and enjoy the beauty of rare and exotic trees, I still find myself attracted to the subtle hues of our native trees – the golden brown of beech and the dull bronze, tannin-laden leaves of oak. It’s the foil of these native trees that enhances the kaleidoscope of the exotics.

Let’s hope that this autumn is dry, with sunny days and cool but frost-less nights. If it is, then we’re in for another peak display of nature’s hidden pigments.

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W A K E H U R S T V I E W

Acer rubrum ‘October Glory’

makes a stunning contribution to the

autumn spectacle at Wakehurst

The Chinese tupelo’s autumn leaves get their vibrant hues

mainly from carotenoid pigments (as do carrots)