The full monty

One of the less heralded aspects of

climate change is that leaves are falling later. I have photographs of Longmeadow carpeted in uncollected leaves in the second week of October, all of them frozen hard. But that hard frost is the key. We rarely get a frost in October at all now and if we do it is a milksop affair, too mild to freeze the leaves from the trees.

But November comes and with it normal leaf-fall service is resumed, and down they all come – streaming, drifting, tumbling and, if there is a proper frost, clattering to the ground. Leaves convert starch from the roots into sugar to feed the tree, but cold nights stop it moving that sugar back to the roots, so it accumulates in the leaves and it is this build up of sugar that results in red pigmentation. The greater the difference in temperature between day and night in late summer and early autumn, the more extreme the leaf colouration will be – which is why the east coast of America with its more extreme, continental climate, invariably has a more dramatic autumnal display than we ever have in Britain.

Gradually, from the first poplar leaves in September to the last oak leaves dropping at Christmas time, or even in the new year, cells break down in the layer between leaf stalk and twig, causing the leaves to fall. A corky scar forms over the resulting wound, protecting the tree from infection, although some trees – such as beech and hornbeam – do not form this scar so hang onto their old leaves until the new ones are ready to push through. The lack of leaves over winter also dramatically reduces the demands on the roots. If the weather is mild and the soil slow to cool down the roots will continue to grow without the demands made on it to supply the leaves. But if it gets cold and the roots stop growing then the tree effectively goes dormant until spring.

Which brings us to the garden gold that is leafmould. Anyone who has read these pages over the past 20 years or watched Gardeners’ World on TV knows that I am evangelical about leafmould. Sieved and cleaned from stones and sticks it transforms ordinary potting compost into a wonderful light texture that is good for anything, but especially all bulbs and plants like fuchsias or maples that like a really loose rootrun, and I use it for potted ericaceous plants like rhododendrons, blueberries and sarracenias.

Used straight fro