Benefits of Proper Mulching

  • Helps maintain soil moisture. Evaporation is reduced, and the need for watering can be minimized.
  • Helps control weeds. A 2-4 inch layer of mulch will reduce the germination and growth of weeds.
  • Mulch serves as nature’s insulating blanket. Mulch keeps soils warmer in the winter and cooler in the summer.
  • Many types of mulch can improve soil aeration, structure (aggregation of soil particles), and drainage over time.
  • Some mulches can improve soil fertility.
  • A layer of mulch can inhibit certain plant diseases.
  • Mulching around trees helps facilitate maintenance, and can reduce the likelihood of damage from “weed whackers” or the dreaded “lawnmower blight.”
  • Mulch can give planting beds a uniform well-cared-for look.

Problems Associated with Improper Mulching

  • Deep mulch can lead to excess moisture in the root zone, which can stress the plant and cause root rot.
  • Piling mulch against the trunk or stems of plants can stress stem tissues and may lead to insect and disease problems.
  • Some mulches, especially those containing cut grass, can affect soil pH. Continued use of certain mulches over long periods can lead to micronutrient deficiencies or toxicities.
  • Mulch piled high against the trunks of young trees may create habitats for rodents that chew the bark and can girdle the trees.
  • Thick blankets of fine mulch can become matted, and may prevent the penetration of water and air. In addition, a thick layer of fine mulch can become like potting soil and may support weed growth.
  • Anaerobic “sour” mulch may give off pungent odors, and the alcohols and organic acids that build up may be toxic to young plants.

Proper Mulching

It is clear that the choice of mulch and the method of application can be important to the health of landscape plants. The following are some guidelines to use when applying mulch.

Inspect plants and soil in the area to be mulched. Determine whether drainage is adequate. Determine whether there are plants that may be affected by the choice of mulch. Most commonly available mulches work well in most landscapes. Some plants may benefit from the use of a slightly acidifying mulch such as pine bark.

If mulch is already present, check the depth. Do not add mulch if there is a sufficient layer in place. Rake the old mulch to break up any malted layers and to refresh the appearance. Some landscape maintenance companies spray mulch with a water soluble vegetable-based dye to improve the appearance.

If mulch is piled against the stems or tree trunks, pull it back several inches so that the base of the trunk and the root crown is exposed.

Organic mulches are usually preferred to inorganic materials due to their soil-enhancing properties. If organic mulch is used, it should be well aerated, and preferably, composted. Avoid sour-smelling mulch.

Composted wood chips can make good mulch, especially when they contain a blend of leaves, bark, and wood. Fresh wood chips may also be used around established trees and shrubs. Avoid using non-composted wood chips that have been piled deeply without exposure to oxygen.

For well-drained sites, apply a 2-4 inch layer. If there are drainage problems, a thinner layer should be used. Avoid placing mulch against the tree trunks. Place mulch out to the tree’s drip line or beyond.

Remember: if the tree had a say in the matter, its entire root system (which usually extends well beyond the drip line) would be mulched.