Benefits of Mulching

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A mulch is any material, organic or inorganic, that is placed on top of the soil in a garden or landscape.  Mulches are one of a gardener’s most valuable tools and an essential component of low-maintenance landscapes.

Benefits of Mulches

Aside from their decorative value, mulches offer many benefits to your soil and plants.  Mulch reduces the amount of water lost through evaporation by shielding the soil from the sun’s drying rays.  It keeps the soil cooler during the summer and acts as an insulator through the cold winter months lessening the effects of fluctuating temperatures on plant roots which in turn decreases their susceptibility to frost heaving.   Organic matter is added to the soil as the mulch breaks down.  Increasing the soil organic matter will improve a soil’s moisture and nutrient holding capacity, structure, and drainage.  Mulch also encourages the activity of beneficial soil organisms.  Weed growth is suppressed by the use of a mulch as is the spread of some plant diseases.  Mulched plots are also less prone to erosion.

Organic Versus Inorganic

Organic mulches are derived from natural materials that decompose over time. As organic mulches decompose, they add nutrients and organic matter to the soil and beneficial microorganisms like nitrifying bacteria and mycorrhizal fungi are enhanced while undesirable pathogens — those that cause plant diseases are inhibited. Increased amounts of organic matter will improve soil tilth and drainage, increase soil moisture retention, reduce soil compaction, and attract earthworms. Because organic mulches decompose, they need to be replaced.  Depending on the type of mulch used, replacement intervals vary from one to four years.

Inorganic mulches include stones, geotextile mats and landscape fabrics, and plastic mulches. Landscape fabrics and plastic mulches deteriorate with time and eventually require replacement.  Inorganic mulches usually are more tedious to install and may require irrigation because water penetration may be limited.  Some inorganic mulches are designed to reflect the sky to confuse and keep insects from landing on plants.  Many do not have a natural appearance and are often covered by an organic mulch for decorative purposes.

General Tips for Applying Mulches

  • Do not place mulch directly against plant crowns or tree bases. Mulch placed directly in contact with stems or tree trunks may retain excess moisture around the base of the plant that can favor the development of diseases like crown rot. Mulch piled around plants may also serve as lodging for bark and stem eating rodents.
  • Mulch applied too thickly can cause problems.  A wood-derived mulch may undergo high temperature decomposition causing it to dry out.  The mulch may then be colonized by fungi that create water repellent conditions throughout the mulch.  Water is unable to penetrate the mulch and reach the soil and plants fail to receive adequate moisture. Mulching too deeply can also cause the soil to remain continuously wet contributing to root and stem rot problems in addition to depriving plants of needed oxygen.  Apply a mulch layer no more than 1 to 3 inches thick.
  • Thoroughly water newly installed wood or bark mulches.  Many good quality mulches are stored in large piles that reach high temperatures.  When the mulch is spread or bagged, the high-temperature tolerant microorganisms that inhabit the mulch die as the mulch cools.  If the mulch is allowed to dry out or remain dry, nuisance fungi can colonize the mulch and create a water-repellent surface.
  • Add a source of nitrogen to garden soils before applying woodderived mulches.  Soil microorganisms that decompose organic materials such as wood-based mulches are effective competitors for limited soil nitrogen. This may cause temporary nitrogen deficiencies especially in annual and perennial plants. Yellowing of leaves often indicates a nitrogen deficiency. Lightly incorporate a source of nitrogen such as bloodmeal, urea or a high nitrogen lawn fertilizer before applying mulch.
Mulch Basics
Soil Nutrient Analysis Laboratory 

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