Mulch is a widely used term in gardening and landscaping, describing any material spread over the soil surface to modify growing conditions. While people often use the terms mulch and bark interchangeably, these materials have significant distinctions that impact their performance. Understanding the composition and application of each is helpful when selecting the right material, depending on needs for longevity, soil amendment, and aesthetic preference.
Mulch as a Category, Bark as a Component
Mulch represents a broad category encompassing any material used as a protective soil covering. This includes organic materials such as compost, straw, shredded leaves, and wood products, as well as inorganic options like plastic sheeting, gravel, or rubber crumb. The primary function of mulch is to conserve soil moisture, regulate soil temperature, and suppress weed growth.
Bark is a specific type of organic mulch derived exclusively from the outer layer of trees. This means that while all bark is considered a type of mulch, not all mulch is composed of bark.
Composition and Processing Distinctions
The preparation process is a major factor separating bark from generic wood mulch. Bark is mechanically stripped from the tree trunk, often from species like pine, cedar, or various hardwoods. This material is then typically processed into uniform shapes, such as distinct nuggets or shredded strands.
Generic wood mulch, in contrast, is made from a wider variety of source material, often including the inner wood (sapwood), branches, and sometimes even whole trees. This material is typically chipped or shredded, resulting in an end product with a more varied and less uniform texture. The inner wood is less dense and more porous than the waxy, fibrous nature of the outer bark.
The source difference also affects the chemical makeup. Bark contains natural compounds, like tannins and natural waxes, which act as a defense mechanism for the tree. These compounds make bark inherently more resistant to decay and decomposition than the cellulose-rich inner wood found in many shredded wood mulches.
Practical Application: Longevity and Aesthetic Choice
The natural resistance of bark translates directly into a longer lifespan in the garden. Bark mulch, especially in the form of chunky nuggets, decomposes slowly, meaning it requires less frequent replenishment, sometimes lasting for several seasons. This makes it a preferred choice for permanent plantings, such as foundation shrubs or mature trees, where minimal maintenance is desired.
Shredded wood mulch, which contains more sapwood, breaks down at a comparatively faster rate. While this quicker decomposition means more frequent application, it provides a faster release of organic matter and nutrients into the soil. This rapid soil enrichment can be beneficial in annual garden beds or areas needing immediate soil improvement.
Aesthetically, bark nuggets tend to maintain their shape and natural color for an extended period, providing a more polished or uniform appearance in ornamental landscape beds. Shredded wood mulch is often favored for functional reasons, as its interlocking fibers help it knit together. This interwoven structure makes shredded mulch an excellent choice for use on slopes and inclines, where it is less likely to wash away during heavy rain events.