Autumn: when every leaf is a flower

When pears and apples start falling, it's not just a signal to bring out the bottles and preserving pan, but an indication the trees are shutting down for the winter.

The other sign is, of course, the changing colour of deciduous trees, their splendid displays a last gasp before the ageing leaves fall.

The common year-round colour of leaves is green, reflecting the presence of chlorophyll, while carotenoids are responsible for yellow, orange and brown, anthocyans give red, and anthoxanthins determine white to yellow in plants.

In autumn, deciduous trees respond to the shorter daylight hours that mean winter is coming, but they also react to soil moisture and temperature. That is why a warm, dry autumn with chilly nights generally gives the best display of leaf colour.

Before the leaves fall, or are blown off, the pigments in them begin to break down, creating a colour palette of golds, purple and scarlet.

At the same time as the colour changes, a layer of cells forms at the base of each leaf. The function of these cells is to seal off the tissues between the leaves and the tree until the leaves no longer have a grip and fall off.

The same process (abscission) occurs with fruit, which - like leaves - falls off when the separation of two walls of cells, one on the stem, the other on the tree, is complete.

Most important for the gardener is knowing when to pick, as different varieties are ready at different times. Lift the fruit gently, so the stem is at right angles to the branch and give a slight twist. Fruit that is ready will come away easily, while pulling hard is likely to tear off new growth spurs, meaning no fruit next season.

Pears will come off while they are still hard. Pick them on a dry day and store in a single layer until soft enough to preserve or eat.