The root ball is the dense mass of roots and the surrounding soil or growing media directly beneath a plant’s stem. This cohesive unit holds the plant together when it is removed from the ground or a container for transplantation. Its integrity is a direct measure of the plant’s ability to survive the stress of being moved. Protecting the root ball is fundamental to minimizing transplant shock and ensuring the plant successfully establishes itself in the landscape.
Formation and Function of the Root Ball
The structure of a root ball depends on how the plant was grown. Field-grown plants are harvested using the “Ball and Burlap” (B&B) method, where roots and native soil are mechanically dug out and wrapped in burlap or a wire basket for transport. Container-grown plants form a root ball shaped like the pot, composed of roots interwoven with the potting mix.
The primary function of the root ball is two-fold, serving both a mechanical and biological role. Mechanically, the dense mass provides physical support and anchorage after planting. Biologically, it concentrates the fine feeder roots responsible for absorbing water and dissolved nutrients from the soil.
Feeder roots are the most actively growing part of the root system. When a plant is transplanted, a significant portion of its root system is lost, making the survival of the remaining feeder roots within the root ball paramount. The concentrated presence of these roots allows the plant to continue drinking and feeding itself, sustaining the foliage above ground until new roots can grow out into the surrounding native soil.
Recognizing Signs of Root Ball Health
A healthy root ball is the best predictor of a plant’s future success. Healthy roots are typically white, tan, or light brown, indicating an active and efficient root system. When gently removed from a container, a healthy root ball should hold its shape firmly without crumbling, yet still feel somewhat pliable to the touch.
An unhealthy root ball often shows signs of distress or decay. Dark colors, such as black, gray, or dark brown, often signal root rot or necrosis if the roots are slimy or mushy. A foul odor is another sign of decay due to waterlogging or poor drainage.
A common problem in container-grown plants is being “root-bound,” where the roots have grown into a tight, circling spiral that conforms to the shape of the pot. These circling roots, sometimes called girdling roots, will continue to grow inward and can eventually choke the plant’s trunk or main root system as they thicken. Roots visible protruding from the top of the soil or drainage holes indicate this condition.
Essential Steps for Planting and Preparation
Preparing the root ball correctly transitions the plant from its nursery environment to the landscape. For container plants, the pot must be removed, and any visible packaging discarded. For B&B plants, the top portion of the burlap and wire basket material should be removed once the plant is situated in the planting hole, ensuring the roots are not restricted.
Addressing circling or girdling roots is mandatory for container-grown plants to encourage outward growth. This is done by using a sharp knife or hand pruners to make four vertical slices, one to two inches deep, down the sides of the root ball. Alternatively, the outer layer of matted roots can be “shaved” off, stimulating the growth of new, regenerative roots into the native soil.
Proper placement in the planting hole requires ensuring the root flare is exposed, which is the area where the trunk widens out at the base. The top of the root ball should be level with or slightly above the surrounding grade to prevent the trunk from being buried too deeply, a common cause of long-term plant decline. Before backfilling the hole, the root ball should be thoroughly hydrated by soaking it.