Gardens
The tints that glow
Ursula Buchan
ummy, why didn't God come down as a woman?'
`Eat up your Real Ghostbuster Spaghetti Shapes, dear.' `Mummy, why has Mrs Harris got a moustache?'
`Don't talk with your mouth full and take your elbows off the table.' `Mummy, why do leaves change colour in autumn?'
`I'm so glad you asked me that, darling. Well . .
Curiously, this is not a question I have ever been asked by a grown-up. Why or how leaves change in the season of mist and party conferences appears to be one life's unexplained mysteries that do not worry us, like how a tin-opener works or the secret of Joan Collins's eternal youth.
In fact I am not the best person to ask, since I do not, know my arginine from my elaioplast, having slept untroubled through many plant physiology lectures. What I do know is that besides the green-reflecting chlorophyll there are other pigments in the leaf which are unmasked — revealing their true colours — as the chlorophyll begins to break down with the onset of shorter days. These are carotene and xanthophyll (which appear yellow) and anthocyanins (red and purple). Some anthocyanins are manufac- tured at this time, particularly when there is still substantial food in the leaf, as is the case after a good summer. What the function of these pigments is, besides gratifying our visual sense, is something about which botany books are tantalisingly vague. There is no mystery, however, about the fact that there are good and bad years" for autumn colour. Cold nights after sunny days in autumn promote it, but sharp frosts, drought and high winds bring it to a premature end, by causing the leaves to drop. A shortage of ground-water can hinder good colouring but, generally speaking, summers with plenty of sunshine encourage it. The brilliance of the Fall in the north-eastern states of America can be attributed to the preponderance of hotter, brighter summers which ensure that the sugar maples, Acer saccharum, colour bet- ter and more reliably than they do in this country.
Autumn colour, good or bad, depends as much or even more, however, on the particular species as it does on season or climate. The gardener who wants a colour- ful autumn garden can therefore make a reasonably informed choice in order to achieve it. The range extends from pale yellow through orange and red to deep purple, occasionally all on the same plant as the leaves age. Dependable are maples (Acers), birches, beech, parrotia, rhus, rowans, deciduous berberis, Virginia creeper and the Japanese vine, Vitis coig- netiae. Some clones (strains) of particular species are more reliable or exuberant colourers than others: that is why the gardener plants the Sweet Gum, Li- quidambar styraciflua 'Lane Roberts', if he can find it, rather than the type species.
Not everyone realises that there is such a thing as a deciduous conifer, let alone one which colours well, but if I gardened in more spacious circumstances I would grow the Swamp Cypress (which does not need a swamp to thrive), Taxodium distichum, for the bright emerald green of the new needles in spring which turn to the rusty brown of a Highland cow in autumn. The larch will do the same in spring but goes a pretty yellow in the 'back-end', as we Midlanders picturesquely call it. (Inciden- tally, some herbaceous perennials, such as paeonies and ornamental rhubarbs [rheums], also colour up.) Although there is no better place to see good autumn colour than a beech wood, those who crave a wide variety of 'tints' should visit one of the country's tree collections such as the Westonbirt Arboretum near Tetbury. Here there are plantings specifically designed for autumn splendour, such as the group of Japanese maples called the Acer Glade. So bright are the carmine-reds, crimsons and scarlets that, in the interests of health and safety, they should be viewed by those with weak eyes only through smoked glass.
The species can also dictate the timing of colouring. In the days when there were such things as common elms, their yellow colour was reckoned to be at its best within a few hours of 7 November.
'Why?'
Er . . . . Good heavens, is that the time? Shouldn't you be in bed?
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