Gardening in the Sky: Cycling Sun and Shade

Sumacs spread, forming a dense grove.

When a tree dies in the garden, plants that were growing in shade may suddenly be exposed to full sun. How do gardeners prepare for such dramatic shifts in light?

One method is cycling. By allowing younger trees to fill in around an older tree, gardeners can ensure that when the larger tree dies, there will be a small to mid-size tree to take its place. This process works especially well with sumacs, which are relatively short-lived. Sumacs spread aggressively through suckering – sending up new stems from the roots – to form dense colonies. Such colonies are a common sight along our local highways and are sometimes mistaken for the tree of heaven (Ailanthus altissima). While the parent sumac may only live for twenty or thirty years, the colonies of its genetically identical offspring can survive for hundreds of years. Left unchecked, a sumac colony will spread in all directions.

Young sumac trees grow around a more established tree. Produced from the root of the older tree, these smaller sumacs are clones of the parent.

With regular maintenance, High Line gardeners keep the trees contained, creating predictable areas of shade and reserving open spaces for sun-loving plants. Like most things in horticulture, the process of cycling requires the patience to wait out awkward moments when plants are not precisely where you want them to be. Rather than trying to keep the garden identical from one season to the next, we work with natural changes to gradually bring the garden toward a balance of sun and shade.

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