While you may think that spring is the ideal time to plant, many plants, including perennials, will be grateful for a head start if you plant them in the autumn. German gardener Oliver Fink, chairman of the Association of Garden Tree Nurseries, is convinced that autumn is the best time for a garden makeover. Conditions are ideal, he says, as the soil is still warm, but the plants’ metabolism starts to slow down. Plus, it’s no longer as hot as in summer. If you plant or transplant now, most plants will begin to form roots without sprouting, Fink says. Planting in autumn therefore helps to prepa…