When to Trim Shrubs?
Like the saying goes, “timing is everything,” particularly when it comes to trimming plants and shrubs. Pruning at the wrong time can leave plants misshapen, make them vulnerable to disease and damage from winter temperatures, or reduce flowering. Other important factors include using clean, sharp pruning equipment such as shears or loppers and using proper pruning techniques to reduce plant damage. Since flowering shrubs form next year's buds at different times of year, gardeners should time trimming projects according to each plant’s flowering schedule.
Winter is a busy pruning season. According to “Sunset,” it is an ideal time to trim woody shrubs to keep them from becoming leggy during the growing season. It is also a good time to prune shrubs that bloom in late summer and fall. For example, western mugwort (Artemisia ludoviciana "Valerie Finnis") is hardy in U.S. Department of Agriculture zones 5 through 10. It grows 1 1/2 to 2 feet tall and blooms from August through September with white flowers. According to the University of California Alameda County Master Gardeners, winter is also a suitable time to prune butterfly bush (Buddleia davidii), California fuchsia (Zauschneria californica) and roses.
Although mild-climate gardeners are predominately busy with planting and preparing soil for planting, gardeners who live in frost-prone areas may want to skip pruning frost-tender shrubs in winter. Wait to prune shrubs that could be damaged or killed by a late winter or early spring frost. One example, Mexican bush sage (Salvia leucantha), is hardy in zones 9 through 11. This evergreen shrub grows 3 to 6 feet tall and blooms with purple or white flowers from summer until the first frost. For frost-tender plants, the extra branches and growth protects them cold weather damage. According to North Coast Gardening, other frost-tender plants include Fairy fuchsia (Fuchsia thymifolia) or citrus-bearing plants.
Although winter and spring are a busier time for trimming shrubs, summer is the ideal time to shear summer-flowering hedges such as boxwood (Buxus "Green Velvet"). Green velvet boxwood is hardy in USDA zones 4 through 9, and it should be pruned after its spring flush of growth has finished to control growth and maintain hedge size. Other candidates for summer pruning include late-flowering perennials such as a double reblooming azalea (Rhododendron "RLH1-2P8" P.P. #21,477). This cultivar, hardy in USDA zones 5 through 9, blooms once in April and again in July. Pruning it before the second bloom would remove its buds and prevent its second bloom. Similarly, Oakleaf hydrangeas (Hydrangea quercifolia), hardy in USDA zones 5 through 9, should be bloomed after the plant has finished blooming in mid to late summer.
When to Deadhead
Most flowering shrubs benefit from the removal of spent blossoms, a process commonly known as deadheading. Trimming dead flowers can be done anytime during a shrub's blooming season. This kind of trimming prevents the shrub from using energy to form seed heads, often encouraging it to bloom more profusely or bloom for a second time.
- Sunset: Northern California Checklist: February
- Missouri Botanical Garden: Artemisia Ludoviciana 'Valerie Finnis'
- Alameda County Master Gardeners: Your Alameda County Garden, Month-by-Month
- North Coast Gardening: What NOT to Prune in Winter
- Fine Gardening: Salvia Leucantha (Mexican Bush Sage)
- Sunset: Northern California Checklist: June
- Monrovia: Green Velvet Boxwood
- Monrovia: Bloom-A-Thon Pink Double Reblooming Azalea
- Missouri Botanical Garden: Hydrangea Quercifolia
Caryn Anderson combines extensive behind-the-scenes writing experience with her passion for all things food, fashion, garden and travel. Bitten by the travel bug at the age of 15 after a trip to Europe, Anderson fostered her love of style and fashion while living in New York City and earning her degree at New York University.