September is a pivotal time of year. The month seems to start in high summer and somewhere around the middle it turns the corner towards autumn. The wildlife in the garden offers no end of hints that the season is changing. Among the songbirds, most of the summer visitors are well on their way to warmer climes for the winter by now. Late summer caterpillars are heading for places to pupate and overwinter in their chrysalises. The resident birds give up the noisy battle over territory and adopt warm roosts each evening, while this year's fox cubs stake out their new territory, independent of their parents. In the plant world, seeds and fruit are ripening, and leaves are taking on the first touch of autumn colour.

In the garden, it is time to start planning to make the most of next spring's reawakening. There are spring bulbs to plant, nest boxes to reposition and seeds to sow. So, while the mood in late September may be a touch melancholy, the dying summer garden should be filled with optimistic thoughts of spring.

Caterpillars will soon cocoon themselves for the winter. The sycamore moth caterpillar is particularly eye-catching as it builds up its energy store.

Nest boxes provide accommodation for all manner of wildlife. The egg-laying season may be months away, but small birds often roost in vacant boxes on cold winter nights. Bats sometimes hibernate in them and butterflies, such as the small tortoiseshell, peacock and brimstone, will overwinter there.

This is a good time of the year to clean out old nesting debris and scald the inside of the box with boiling water to reduce the risk of pests and diseases reinfecting next year's young birds. If you failed to attract nest-builders last spring, try moving the box to a new position in the garden, out of the sun and preferably camouflaged by foliage.

The shrew population reaches a peak in late summer, but these tiny carnivores rarely live much more than a year. By late September, those that were born last year start to die. You may see their small corpses beside garden paths, but rest assured that there will be a whole new generation of young shrews to do battle with your smaller garden pests and renew the population next spring.

Deadhead buddleia as the flowers fade. This makes it quite possible to maintain a continual supply of nectar well into the autumn. The later sprays will be smaller than the earlier ones, but they are particularly valuable as a food supply for bees and a variety of butterflies in September.

A good many moths and butterflies survive the cold winter in a state of suspended animation, wrapped inside a tough, protective chrysalis. September is the last chance for caterpillars to gorge themselves and build up a store of energy.

Watch out for the particularly striking sycamore moth larva, Acronica aceris. In September, it marches down from the canopy of its chosen tree to hide away in the soft soil around the roots as an inconspicuous chrysalis until next year.