Proper Mulching Techniques
Mulching is one of the most beneficial practices a homeowner can use for better tree health.
By TreesAreGood®
International Society of Arboriculture
What are Mulches?
Mulches are applied to the soil surface to maintain moisture and improve soil conditions. However, if misapplied, mulch may have little, or even negative, impact on the trees in your landscape.
Benefits of Mulch
• Reduces soil moisture loss through evaporation
• Controls weed germination and growth
• Insulates soil, protecting roots from extreme summer and winter temperatures
• Improves soil biology, aeration, structure, and drainage over time
• Increases soil fertility
Why Use Mulch?
Urban landscapes are typically harsh environments with poor-quality soil. Many benefits of the natural environment can be replicated, while maintaining a more formal appearance, with the application of mulch.
Organic Mulches
Organic mulches are generally composed of a variety of products usually derived from plants and decompose in the landscape at different rates depending on the material, climate, and soil microorganisms present.
Inorganic Mulches
Inorganic mulches include various types of stone, lava rock, shredded rubber, and other materials. They do not decompose and do not need to be replenished often, however, they do not improve the soil structure or provide nutrients.
Not Too Much
Too much mulch can be harmful. The recommended mulching depth is 2–4 inches (5–10 cm). While organic mulches must be replenished over time, buildup can occur if reapplication outpaces decomposition or if new material is added simply to refresh color.
Rodents and Insects
Mulch piled high against the trunks of young trees may create habitats for rodents that chew bark. It can also soften the tissues making them more susceptible to the development of insects and disease problems.
Water Control
Thick blankets of fine mulch can become matted and may reduce the penetration of water and air. On wet soils, applying too much mulch can reduce soil drying, lead to excess moisture in the root zone, which can stress the plant and cause root rot. In these cases, it may be best to leave bare ground exposed or to apply a thin layer of an inorganic mulch.
How Much Mulch
In well-drained sites, apply a 2–4 inch (5–10 cm) layer of mulch. Fine mulches, such as composed materials, should be applied in a 2–3 inch (5–7 cm) layer and coarse mulches, such as arborist wood chips, should be applied in a 3–4 inch (7-10 cm) layer.
From Trunk Base to Dripline
If mulch is piled against the tree trunk, pull it back several inches/centimeters so that the base of the trunk is exposed. Extend the mulch to the drip line of the tree. If it is not practical or space is limited, apply as far as you can. Generally, a 3 foot (1 meter) radius ring of mulch is the minimum for most trees.
TreesAreGood Organic Mulch by Jon MooreTreesAreGood®
Soil pH
Some mulches, especially those containing fresh grass clippings, can affect soil pH and may eventually lead to nutrient deficiencies or toxic buildups. Anaerobic “sour” mulch may give off pungent odors, and the alcohols and organic acids that build up may be toxic to young plants.
The Right Kind
If the species you are mulching has symptoms related to a pH problem, select a mulch that can aid in correcting the problem.
If mulch is already present, check the depth, break up any matted layers and refresh the appearance with a rake. Some landscapers spray mulch with a water-soluble, vegetable-based dye to add color to faded material.
Visit TreesAreGood.org for more information and free, downloadable brochures.
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