How to - Techniques

Stimulate growth by learning to trim at the right time


Spring is the time to prune woody plants to remove damaged or diseased branches, to rejuvenate old shrubs to promote flowering or improve their shape, or to ensure safety. Yet pruning is a task that daunts gardeners because they're afraid of making a mistake. Take heart. You're unlikely to kill the plant, and any bad errors should eventually disappear as it grows.

In fact, pruning stimulates growth. When you cut back a shoot, you cause buds on the remaining part of the branch to break into growth. Note, however, that a characteristic known as apical dominance causes the topmost buds to grow the fastest and the longest. This is useful if, for example, there is a hole in a tree, shrub or hedge that you want to fill. By pruning surrounding branches back to a bud pointing toward the hole, you can encourage growth into the empty area.

Bush whack
Shrubs that bloom in spring and early summer should be pruned shortly after they flower. Some species grow slowly and only need to be pruned occasionally, but if they're overgrown, now is the best time to shape them. Shrubs that bloom later, in summer or fall, normally flower on the new season's growth and should be pruned in spring to promote a vigorous crop of new shoots (thus encouraging abundant flowering).

Prune certain shrubs (list provided below) before their buds break in early spring. Names marked with an asterisk should be cut back hard; for the rest, simply remove the oldest branches as needed.

Shrubs such as yellow-twigged and red osier dogwoods (Cornus alba and C. sericea) and ‘Flame' willow (Salix ‘Flame'), which are all grown for their brightly coloured bark, should be cut back hard every two or three years, since their new growth has the brightest colour. Treat yellow-leafed elderberries, such as ‘Sutherland Gold' (Sambucus racemosa ‘Sutherland Gold') in the same way.

Shrubs you can prune worry-free

  • Japanese angelica tree (Aralia elata)
  • Butterfly bush (Buddleja davidii)*
  • Bluebeard (Caryopteris x clandonensis cvs.)*
  • Bush honeysuckle (Diervilla spp.)*
  • Common witch hazel (Hamamelis virginiana)
  • Rose of Sharon (Hibiscus syriacus)*
  • Annabelle hydrangea (Hydrangea arborescens ‘Annabelle')*
  • PeeGee hydrangea (H. paniculata ‘Grandiflora')*
  • St. John's wort (Hypericum spp.)
  • Potentilla (Potentilla fruticosa)
  • Ural false spirea (Sorbaria sorbifolia)*
  • Spirea (Spiraea—most species and hybrids)
  • Snowberry (Symphoricarpos albus var. laevigatus)
  • Five stamen tamarisk (Tamarix ramosissima)*

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