Roses grow on fibrous root systems as do other members of the Rosaceae family, including strawberries and blackberries, as well as apple, almond and peach trees. Fibrous roots consist of a top knot or crown that descends as one or more thick roots, from which spread smaller arms and tendril tips. Fibrous roots grow mostly laterally, creating a twining mat for upper soil-level support.
Roses have a root crown from which multiple arms and tendrils grow. This central root develops from a seed and grows downward, forming a "radicle," or root embryo. This original root structure connects and generates growth above and below ground. It develops sprouts that become stems, leaves and flowers while also producing thick arm roots and stringy, fibrous root ends. It's important, when planting bare root roses, to bury the crown only at soil level.
Root arms are the largest growths emanating from the central root crown of a fibrous root system. In roses, they are usually 2 inches or less in diameter but may be several inches long. Root arms emanate from the crown in a twisting or knotted fashion, growing laterally and downward. These dense, fleshy structures stabilize the plant while also absorbing soil nutrients. In addition, they generate the next root level: root tendrils that spread horizontally.
Wiry tendrils 1/2-inch or less in diameter emerge from the root arms, spreading in all directions but most often horizontally, near the tops of the larger, arm-like formations. These structures, along with the tiny, hair-like fibers they create, make up the fibrous texture of this root type. Small but strong tendrils form a lateral, underground support network for the plant, allowing it to absorb lots of moisture and larger-molecule soil nutrients, such as magnesium.
At the tips of root tendrils grow tiny root fibers about the size of coarse hairs, or smaller. These structures grow in all directions from the root tendrils, intertwining with them and developing mostly horizontally. Root hairs pull in moisture along with the smallest soil elements, such as oxygen molecules, nitrogen and phosphorous particles. Often root hairs are missing on bare root roses but will redevelop quickly once the main root and arms are planted.