Summersweet (Clethra alnifolia) is a cold-hardy shrub that can be grown in zones 3-9. This moisture-loving shrub needs little preparation for winter other than a generous layer of mulch around its roots to retain moisture. In warmer regions where Summersweet does not go completely dormant, the occasional watering to keep the root zone moist may be necessary.
Protecting Summersweet in Winter
Summersweet is a cold-hardy shrub, able to withstand temperatures as low as -30°F depending on the variety. While some younger and smaller twigs can be damaged by the cold during the winter, an early spring prune will ensure that healthy new growth is produced once temperatures have warmed. To protect Summersweet from the cold, apply 2-3 inches of mulch around the root zone prior to winter. In warmer regions, Summersweet is more likely to be damaged by drought than cold, so checking the soil moisture regularly and water as necessary.
Cutting Back Summersweet For Winter
In colder regions, Summersweet will lose its leaves and go dormant in the winter. Pruning in the fall and winter is not recommended, and major pruning can be done in the early spring to encourage new growth. In warmer regions, Summersweet may keep its leaves and pruning can commence in the early spring as well.
Summersweet Winter Care in Pots
Perennials and shrubs in pots are always more likely to be damaged by extreme temperatures, regardless of their cold hardiness. In colder regions, we recommend placing potted Summersweet in a garage or basement to protect its roots from the cold. In warmer regions, potted Summersweet can stay outdoors and regular watering may still be necessary.
Watering Summersweet in Winter
When in the ground, Summersweet will still do best in consistently moist soil through the winter. In warmer regions, this may mean checking soil moisture regularly and watering deeply as needed. In colder regions, dry roots are more likely to be damaged by extreme cold than those insulated with ice and snow. When warm days come about, check the soil moisture in your garden and water when needed.
When potted, only keep Summersweet outdoors if you are in a region with mild winters. Keep the soil consistently moist through the winter and avoid oversaturating the soil and leaving the roots soggy, which could lead to root rot. In colder regions, Summersweet in pots may still go dormant and not need any regular watering or care.
Growing Summersweet Indoors
Like many other perennials and shrubs, Summersweet is not well suited to be kept indoors long term. In the winter time to protect the roots, it is best to bring potted Summersweet into a dimly lit garage or basement. This allows the plant to go dormant while still being protected from the cold. Flowering perennials and shrubs will often produce better blooms the following season if they are allowed a dormancy period. Keeping your shrubs in a garage will provide them with low enough temperatures to keep them dormant without the risk of damaging their roots.
Steps To Care For Summersweet in Winter
Summersweet is cold hardy and requires little care through the winter. Providing a layer of mulch around the root zone of Summersweet can help protect the roots through the winter in colder regions. The chances of you needing to regularly water this shrub depend on how mild the winters are in your regions. Other than watering in warmer regions, Summersweet can be left alone until the early spring when pruning can commence.
Step 1 - Add 2-3 inches of mulch
Step 2 - In warm regions, water when necessary
Step 3 - Prune in early spring
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Author Lynn Gusman - Published 1-13-2023