PROPER MULCHING TECHNIQUES

    Mulches are materials placed over the soil surface to maintain
    moisture and improve soil conditions. Mulching is one of the most
    beneficial things a home owner can do for the health of a tree.
    Mulch can reduce water loss from the soil, minimize weed
    competition, and improve soil structure. Properly applied, mulch
    can give landscapes a handsome, well-groomed appearance. Mulch
    must be applied properly; if it is too deep or if the wrong material is
    used, it can actually cause significant harm to trees and other
    landscape plants.
    Benefits of Proper Mulching

    • Helps maintain soil moisture. Evaporation is reduced, and the need for
      watering can be minimized.
    • Helps control weeds. A 2- to 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.
    • entrap air polluting gases
    • 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 “lawn mower
      blight.”
    • Mulch can give planting beds a uniform, well-cared-for look.
    Trees growing in a natural forest environment have their roots anchored in a
    rich, well-aerated soil full of essential nutrients. The soil is blanketed by
    leaves and organic materials that replenish nutrients and provide an optimal
    environment for root growth and mineral uptake. Urban landscapes,
    however, are typically a much harsher environment with poor soils, little
    organic matter, and large fluctuations in temperature and moisture.
    Applying a 2- to 4-inch layer of organic mulch can mimic a more natural
    environment and improve plant health.

    The root system of a tree is not a mirror image of the top. The roots of most
    trees can extend out a significant distance from the tree trunk. Although the
    guideline for many maintenance practices is the drip line—the outermost
    extension of the canopy - the roots can grow many times that distance. In
    addition, most of the fine, absorbing roots are located within inches of the
    soil surface. These roots, which are essential for taking up water and
    minerals, require oxygen to survive. A thin layer of mulch, applied as
    broadly as practical, can improve the soil structure, oxygen levels,
    temperature, and moisture availability where these roots grow.

    Types of Mulch
    Mulches are available commercially in many forms. The two major types of
    mulch are inorganic and organic. Inorganic mulches include various types
    of stone, lava rock, pulverized rubber, geotextile fabrics, and other
    materials. Inorganic mulches do not decompose and do not need to be
    replenished often. On the other hand, they do not improve soil structure,
    add organic materials, or provide nutrients. For these reasons, most
    horticulturists and arborists prefer organic mulches.

    Organic mulches include wood chips, pine needles, hardwood and softwood
    bark, cocoa hulls, leaves, compost mixes, and a variety of other products
    usually derived from plants. Organic mulches decompose in the landscape
    at different rates depending on the material and climate. Those that
    decompose faster must be replenished more often. Because the
    decomposition process improves soil quality and fertility, many arborists
    and other landscape professionals consider that characteristic a positive
    one, despite the added maintenance.
    Not Too Much!
    As beneficial as mulch is, too much can be harmful. The generally
    recommended mulching depth is 2 to 4 inches. Unfortunately, many
    landscapes are falling victim to a plague of overmulching. A new term,
    “mulch volcanoes,” has emerged to describe mulch that has been piled up
    around the base of trees. Most organic mulches must be replenished, but
    the rate of decomposition varies. Some mulches, such as cypress mulch,
    remain intact for many years. Top dressing with new mulch annually (often
    for the sake of refreshing the color) creates a buildup to depths that can be
    unhealthy. Deep mulch can be effective in suppressing weeds and reducing
    maintenance, but it often causes additional problems.
    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 matted
      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 are exposed.
    • Organic mulches usually are 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 also may be
      used around established trees and shrubs. Avoid using noncomposted
      wood chips that have been piled deeply without exposure to oxygen.
    • For well-drained sites, apply a 2- to 4-inch layer of mulch. 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.