Gardening: Market gearing up for the autumn plant sales

Growth on the herbaceous type is beginning to decline and deciduous plants are preparing to shed their leaves as they all head toward a state of dormancy. Better still, in the absence of ground frost, the soil retains enough warmth to encourage new root growth on anything planted.

This is the time of year to take liberties unheard of in summer, like digging up existing small trees or shrubs that have shed their leaves and transferring them to a new site.

Invasive perennials seen to be encroaching on their neighbours can now be taken to task, dug out, divided into sections and moved to pastures new.

The bare-rooted planting of certain deciduous specimens is possible because the plant has effectively closed down all top growth for winter. In such circumstances it's not unusual to see tied bundles of young hedging plants, beech, hawthorn, et al on display, or to receive roses, fruit trees, etc via mail order. In all such cases the first step before planting is to plunge the bare roots into a container of water for a few hours.

Nature's equivalent of a firework display is always keenly anticipated and occasionally long-lasting. We view the leaf colour change of autumn as a garden spectacle, eagerly purchasing trees and shrubs with notable colour patterns; maple, cotinus and fothergilla spring to mind.

In essence it's a simple salvage operation, the trees reabsorbing nutrients from the leaves before they fall.

Key plants may start the process in late September, as Koelreuteria (golden rain tree) did recently in The Alnwick Garden. This was followed by Gleditsia, and both have now shed many of their leaves. Other species will join the party much later in November.

Understanding the science behind the process serves to heighten appreciation of this glorious spectacle. Green chlorophyll is the dominant leaf colour throughout the growing season. It is essential to the food-making process, photosynthesis, but it`s presence masks other pigments in red and gold.

The arrival of shorter days and cooler temperatures reduces food production and chlorophyll decreases, revealing orange and yellow carotenoids. Dry, sunny autumn days encourage blue, purple and red anthocyanins to emerge and the display is at it's zenith. Warm, bright days followed by cool nights keep the show on the road.

Once the leaves have gone the window of opportunity for safe plant movement begins. It also applies to evergreens and remains open, in the absence of frost, until spring next year. However, if you`re moving plants or introducing any newcomers during winter, it`s best to do so when a run of mild days is forecast.