The growth of newly planted trees is greatly reduced if the grasses are not kept away with herbicides and mulches until they are well established. Weeds growing around ornamental plantings provide food and cover for rodents during the growing season. This allows their population to increase greatly. After weeds are killed back to the ground by frost, they still provide cover for rodents, but not food. This often results in the girdling of woody ornamental plants by rodents in the winter.
Weeds growing over ornamental plants interfere with pesticide applications.
One of the most important aspects of insecticide or fungicide applications is thorough coverage of the foliage. With weeds covering some of the foliage, thorough coverage is impossible. Plants such as poison ivy, poison sumac, and wild parsnip can cause a severe rash on people that come in contact with them. These weeds must be controlled around homes to eliminate the risks to friends and family, and around public and commercial areas to minimize the liability issue associated with visitors being affected by the plants. Controlling weeds in landscape plantings is much more complex than controlling weeds in turfgrass.