IT'S  autumn, so it's time to get your hedgerows into trim

THE garden teams here at RHS Garden Harlow Carr are busy working their way across the 58-acre garden cutting hedges, tidying wall climbers and clipping to shape the topiary. Every year this job starts in September, after birds have stopped nesting, and will be complete by November. Spare a thought then for the gardeners at Levens Hall in Cumbria: they won't finish clipping their world- famous topiary garden until well into the New Year; by spring the bushes, hedges and 300-year-old sculptures will be crisp and razor sharp for the new season.

Whenever we are engaged in hedge cutting we always get asked to recommend the best plants to make a hedge. There is a kind of league table of hedges; go to any established large public garden or country estate and you will most likely find the following three: firstly, and some would say the ultimate hedging plant is yew Taxus. It is dense and evergreen, with fine needled growth capable of creating small, medium or large topiary shapes. As a hedge, when well cut, it becomes living architecture, very often used to create complete outdoor rooms and solid divisions between spaces.

Next in the top three comes beech Fagus; not evergreen but with a remarkable trick of the leaves up its sleeve. During the growing season the fresh green leaves unfurl to clothe the stems and branches, becoming glossy green to form an elegant backdrop to any garden scene. Once annual growth is taken back in autumn to a desired shape or line, the remaining green leaves eventually shut down as temperatures drop. The trick that beech pulls off requires the bronze papery old leaves to stay attached across the winter only to be shed as new growth starts again in the spring. In this way you get double for your money: a classy green hedge in summer and an equally classy copper-coloured one through the frosty months.

Third up but by no means third rate comes what some regard as the quintessential hedging and topiary plant, box Buxus. Box has an ancient pedigree in providing gardens with green structure and formal sophistication. Dense evergreen, usually dark green leaves, will take very precise formal clipping. The relatively slow growth of Box mean that the shapes created are held over a longer period, generally only needing to be clipped once a year. Great though Box is, it does have one drawback: it is susceptible to the fungal disease box blight which can defoliate affected plants.

Some garden designers now specify similar looking plants like Japanese holly Ilex crenata or Euonymus Green spire for small formal hedges. However, with good air circulation, clipping in dry weather, picking up cut leaves and good garden hygiene, box is still an option if you want that classic formality.

The formal shaping of plants is very often associated with classic sophistication and large landscape gardens but clipped and manicured shapes are perfect for the smallest garden spaces. It allows you to place plants of high ornamental value into tightly trained spaces. By moving away from traditional hedging plants you can start to consider shrubs and trees that respond to clipping to give a different look. Low hedges of lavender or rosemary bring an extra dimension of flower to a garden boundary. Evergreens that flower and then have fruiting berries are particularly attractive: Firethorn Pyracantha and holly Ilex will take very tight formal clipping with the added benefit that their spiky and spiny profiles deter intruders.

Of course, sometimes a garden space is not an option but even one well-chosen pot with a formally- trained evergreen plant can lift your outdoor space. But a word of warning: clipping, trimming and shaping plants can become addictive!