Weeping willow trees grow throughout the United States. Known and named for their long weeping strands of foliage, weeping willow species belong to the Salix genus. Some sources attribute the name weeping willow to a specific species---the Chinese Salix babylonica, for instance---though the name applies to all species of the genus. While they're popular with gardeners and landscapers, weeping willows possess tremendous root systems that impact and alter their surroundings.
Willow trees possess fibrous root systems. Fibrous roots grow in large, dense networks both laterally and vertically; they extend much further in spread than in depth. These root systems produce large primary roots, from which many smaller roots may grow. Willow root systems sometimes exhibit stoloniferous roots, or those that grow above the ground and can produce independent stems. As with all trees with fibrous roots, willows express adventitious qualities, meaning roots grow from plant organs other than the root system, such as the stem.
Weeping willow roots grow great lateral distances from the trunk of the tree in search of moisture. Willows require vast amounts of water to survive, and the root systems of the trees grow aggressively in search of water sources. Weeping willow root systems grow as many as three times the distance of the trunk to the edge of the canopy in all directions. Some willow species exhibit mature spreads of 50 feet or more, or 25 feet in radius. Weeping willow roots may grow as far as 75 feet from the centre of the tree, in all directions.
In their aggressive pursuit of water, weeping willow root systems can cause vast amounts of damage. Roots can tear into sewer systems and septic and water tanks. The roots possess the strength to penetrate and even destroy wood, metal, plastic and concrete. Weeping willow roots destroy sidewalks, streets and the roots of other plants. The trees out compete nearly all species in the surrounding area on account of their root system. Due to these tendencies, sources recommend planting willow trees far from anything the roots may destroy. Willows grow quickly; if planted in an area with numerous obstructions, roots may destroy obstructions before an opportunity to replant arises.
Weeping willows sometimes suffer from root rot, which causes a general decline in health in an infected tree. Various types of root rot exist, most caused by fungal pathogens. Mushroom root rot, for instance, occurs when mushrooms grow on the exposed roots of willow trees, rotting the wood. Root rot inhibits a tree's ability to draw moisture and nutrients from soil, and may impact the structural integrity of a tree. The destruction of a major root can cause willow trees to collapse. Verticillium root, another fungal disease, travels through soil and may enter willow trees through the roots.
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- University of Florida IFAS Extension; Salix spp; Edward F Gilman et al
- "Identification, Selection and Use of Southern Plants"; Neil G Odenwald et al; 2006
- University of the Western Cape: Different Types of Roots
- Ohio State University Extension: Ohio Willow Trees
- North Dakota State University; Deciduous Tree Diseases; RW Stack et al; 1995
- Fine Gardening: Genus Salix