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Autumn encore

25 October 2013

iStock

WE HAVE a former Bishop of London, Henry Compton, to thank for one of the best garden trees for autumn-leaf colour.

Liquidambar styraciflua was introduced in 1681 from its native North America by John Banister, sent by the botanising Bishop to spread the good news and bring back interesting plant specimens. The sweet gum is still grown in Fulham Palace gardens today.

This narrow tree, growing to about six metres after ten years, and maybe 15 metres ultimately, has attractive lobed leaves, reminiscent of a vine, which take on the most beautiful autumn colouration. Even a single leaf displays the spectrum of hues that reveal the science behind the seasonal show.

Some green may remain where the main photosynthetic pigment, chlorophyll, still lingers, but, where this has broken down, yellow and orange carotenoid pigments are revealed. Splodges of burgundy show where anthocyanins (which give red wine its colour) have been generated by the breakdown of surplus sugars.

Since the introduction of the straight species to Britain, numerous cultivars of L. styraciflua have been selected. "Lane Roberts" can be relied on for a particularly vinous autumnal hue; "Worplesdon" has leaves with more pronounced lobes, that tend more towards orange and yellow for their swansong; and "Slender Silhouette" has an exaggerated columnar habit: it rarely grows wider than a metre, making it more suitable for a smaller garden. It still gets tall, however.

Parrotia persica is a large shrub of spreading habit, which displays brilliant crimson-and-gold autumn colour, and mottled bark that flakes with age like that of the London Plane. More suited to gardens of modest size is Parrotia subaequalis.

Some climbers make quite a show as the days shorten. Parthenocissus henryana is self-clinging, and turns purplish and then fades to orange-red over six to eight weeks. Colour is most pronounced when the plant faces north or east.

For a sunnier aspect, try the purple-leaved grape Vitis vinifera "Purpurea", or another vine with large heart-shaped leaves, Vitis coignetiae. I have grown the latter in a small raised bed, from which the rampant growth travelled far and wide. I trained it along wires, across the courtyard setting, to provide shade in summer before the October colour-fest.

If you have space for a few pots, you can grow Acers, and easily give them the acid substrate they need by way of an ericaceous compost. My winner is "Osakazuki" for its brilliant cloak of red that resists scorching.

The chemistry of autumn colour is influenced by the weather, which explains why some years are more spectacular than others. The best are when warm, dry, sunny days are followed by cold but not frosty nights. This combination is more prevalent in the "fall" of New England than in damper, duller Britain. But it also about genetics; so choosing a few plants with a predisposition to fireworks can really add to the garden's finale.

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