Many plants need a rejuvenating moment in their lives, just as I do. I like to take some time off at the beach or maybe a hike in Umstead State Park.
Since plants can’t go for a swim in the ocean or take an afternoon hike, they need other forms of rejuvenation. Even a plant that has received normal moisture, drainage and feeding for years may still develop poor growth habits, and a nice heavy rejuvenating pruning can usually snap a plant out of the doldrums.
Pruning tactics like this are generally applied to shrubs or small trees. Woody plants need rejuvenation pruning if you start to see old canes beginning to die in the center of the plant, if the plant begins to produce fewer flowers than normal, or if it generally looks thin and spindly.
There are two types of rejuvenation pruning. The first is a “crown thinning,” in which all the dead and weak branches or selected trunks in a multi-stemmed shrub are removed. Shrubs like wintersweet, witchhazel or viburnum will develop weak stems or trunks as they become older; these should be sawn off as low as possible. Removing these allows more light in the center of the plant, thus encouraging more energy to be put into new growth.
The second type of heavy pruning is called a “crown reduction.” That’s when you remove all plant growth back to a certain point on the plant. Hedges needing their overall size reduced may get this type of pruning every three to five years, depending on growth rate and size desired. Evergreen shrubs like hollies, azaleas, wax myrtle and laurel respond well to this type of pruning. Keep in mind that the best time to prune flowering plants is a few weeks after they flower. For evergreen shrubs, it’s in late spring through mid-summer.
Vines may also need to be rejuvenated from time to time. The iconic Chinese wisteria on the pergola at Sarah P. Duke Gardens dates back to 1939, and it has been in a semi state of decline for about 10 years, with severely reduced or no spring flowering. To encourage new growth, it will receive a complete crown removal next summer—basically cutting the vine back to the ground. The strongest new stems will be selected from as it grows back, and within a few years the vine’s flowering should return to its full spring glory atop the pergola.
Bobby Mottern is the director of horticulture at Sarah P. Duke Gardens.