Some branches of this multi-stemmed dwarf lilac need to be thinned to improve air flow and eliminate rubbing stems.
© George Weigel
Pruning is an important and necessary task both for the health and appearance of most woody plants. Many gardeners are reluctant to cut into a healthy tree or shrub, fearful that improper technique will harm or even kill it. Neglect, though, can be worse than incorrect pruning, and the benefits of pruning are many:
- Removing dead, damaged, diseased, or dying foliage reduces the potential spread of wood-rotting diseases and improves to look of the plants.
- Thinning out overly dense growth improves airflow, reducing the odds of damage in windstorms. It also discourages leaf disease.
- Pruning rejuvenates old plants by spurring healthy new young growth and increased bloom.
- Pruning shapes and improves the appearance of plants.
- Pruning can correct potential problems created by less than ideal locations (for example, when a shrub has grown too large for its designated garden space).
When to prune
When you prune depends on what you’re pruning. As a rule of thumb, prune most flowering shrubs after bloom time:
- Varieties that bloom in early spring to mid-June (from buds that formed last summer and fall) such as azaleas, beautybush, chokeberry, daphne, rhododendron, deutzia, fothergilla, forsythia, mophead hydrangeas, kerria, lilac, mock orange, mountain laurel, ninebark, viburnum, and weigela should be pruned immediately after flowering.
- Shrubs that bloom from mid-June on (from buds that formed in the spring) can be pruned at the end of winter or very early spring. Abelia, beautyberry, butterfly bush, caryopteris, crape myrtle, heather, tree-type hydrangeas, potentilla, roses, rose-of-sharon, St. Johnswort, summersweet, and vitex are good examples.
- Needled evergreens, such as arborvitae, hemlocks, yews, Douglas firs, junipers and false cypress are pruned to control size at the end of winter (about March).
- Broad-leaf evergreens grown for foliage including boxwoods, privets, inkberry, and blue hollies, are trimmed at winter’s end.
- To control size in spruces and pines, wait until these have finished putting out their new growth ("candles") toward the end of May. Then remove all or half of the new growth as needed. Avoid cutting back into older wood.
Pruning Do’s and Don't’s
An early-spring “rejuvenation pruning” of this red-twig dogwood will encourage new wood that bears the brightest red bark next winter.
© George Weigel
- Do keep pruning saws and blades sharp, always.
- Do step back and look often while you’re pruning. Once you cut a branch off, you can’t glue it back on.
- Don't cut off more than one-quarter to one-third of a plant’s growth in a single year – as a guideline.
- Don’t “top” trees by shearing off all growth from the tips back. It’ll encourage lots of weak new twiggy growth. Trees will become unsightly and may become prone to wind damage.
- Don’t use tar, paint, or similar wound dressings after pruning. These are not necessary and may encourage rot and disease.
- Don’t climb up into trees to prune. Hire a professional arborist if your bigger trees need work.
- Don’t let plants get so overgrown and out of control that you have to cut off big branches. Big wounds don’t heal as well.