As noted in an earlier post, topiary is defined as ‘the horticultural practice of training live perennial plants by clipping the foliage and twigs of trees, shrubs and subshrubs to develop and maintain clearly defined shapes.’ It’s a moot point when Hedge Trimming becomes true topiary. I don’t think it actually matters and prefer to think of this side of hedge gardening as a just a continuum – to each his own. How your hedge looks is personal – the following main Hedge Trimming styles should get you started…
The ‘standard’ formal style is as suitable for Yew and Hornbeam as it is for Privet and Beech; Box, Griselinia and Pittosporum; Leylandii and Lonicera.
The soft lines of this undulating style requires more careful planning and a little more work but is not difficult. As carpenters say: ‘measure twice, cut once’. Any hedging plant suitable for ‘standard’ styling can be transformed into ‘clouds’.
Spheres, turrets, pyramids, cubes etc. can be created from free-standing specimen plants or incorporated into a full hedge.
There is a fine line between an informal hedge and an untidy one. As a general rule, those hedging plants (typified by Yew, Hornbeam or Privet) suitable for precise trimming look their best when they are given a definitive shape. Freer-growing hedging and edging plants like Escalonia, Perovskia Blue Spire, Cherry Laurel or Photinia Red Robin need to be kept neat but are unsuitable for enforced geometry.
Lavenders and Rosemary sit somewhere between the two.
For animal shapes, complex spirals and similar examples of advanced topiary on a grand scale, Yew, Hornbeam and Privet remain the go-to hedging plants.
NB: if you are unsure, it is probably better to try your hand on smaller hedging plants (say Box or Privet) before taking your shears to an established or growing hedge.