Should I cut perennials back in autumn or leave them standing until spring?

Mostly leave them, with specific exceptions. The old habit of clearing every border to bare soil in October is tidier than it is useful.

Standing stems and seed heads do real work over winter. Hollow stems shelter overwintering insects, including many of the predators that control aphids the following spring. Seed heads feed finches and tits. The dead top growth insulates the crown against hard frost. And frosted grasses, sedum and echinacea are among the few things worth looking at in a January garden.

Cut back in autumn where there is a specific reason. Anything that had a fungal problem — peony with botrytis, phlox or monarda with mildew, hollyhock with rust — should be cut down and the material removed rather than composted, because the spores overwinter on the debris. Plants that collapse into a wet slimy mass, such as hosta and daylily, are better cleared before they smother neighbouring crowns. Aggressive self-seeders should be cut before the seed disperses, unless you want more of them.

Leave everything else until late winter or early spring, then cut back before new growth pushes through — usually February or March depending on climate. Cut to a few centimetres above the crown and take care not to slice emerging shoots.

Evergreen and semi-evergreen perennials such as heuchera, epimedium and hellebore are a separate case: remove only tattered old foliage in late winter, and for hellebores do it before the flowers open so you can actually see them.

If tidiness matters in a front garden, a reasonable compromise is to clear the visible front third and leave the back standing.