Bark Mulch
Bark mulch is bark separated from timber as a byproduct of the forest industry and sold as a landscape mulch. Pine bark is the form the extension sources describe directly and it is covered in detail on this page, which does not mean every product labelled bark mulch is pine bark or that bark products share one standardized makeup. Bark mulch is sold across a range of particle sizes rather than in a single texture, from finely shredded and ground material through to large pieces called nuggets. Those differences in form change how the material behaves: large pine bark nuggets float in water and may not stay in place during heavy rain, and coarse-textured bark such as nuggets allows good air movement through the layer. How much to buy and how deep to spread it are separate jobs, handled by dedicated pages elsewhere on this site.
What Bark Mulch Is
Bark mulch is the bark that comes off logs when timber is processed. Rather than being waste, it is a byproduct of the forest industry, collected and sold on as a landscape mulch — the material was separated from wood already being processed for another purpose. The sources this page relies on describe pine bark specifically: pine bark is a byproduct of the forest industry, and it reaches gardens as ground-up pieces and in nugget forms. Bark also comes from hardwood species, which is why "bark mulch" and "hardwood mulch" overlap in everyday use and why some products are sold under names combining both words. This page describes bark as a material and does not rank materials against one another; hardwood mulch is a separate topic and is not covered here.
The Forms Bark Mulch Comes In
Bark mulch is not one texture. It can be purchased in various particle sizes, from shredded material at one end through to large-sized particles called nuggets at the other, and pine bark in particular reaches gardens both as ground-up pieces and in nugget form. The useful way to picture this is a continuum rather than a fixed set of grades: what mainly separates one bark mulch from another is where its pieces fall along that range, from fine and shredded to coarse and chunky. This page describes that range; it does not define commercial grades or treat any particular size as a standard.
How the Different Forms Behave
Where a bark mulch falls on that size range changes how it behaves once it is spread. Large pine bark nuggets float in water and may not stay in place during a heavy rain — that behaviour belongs to the coarse, large-nugget end of the range rather than to bark mulch in general. Coarse-textured mulches such as pine bark nuggets also allow good air movement through them; like the floating behaviour, this is a property of coarse material specifically and should not be assumed of every bark mulch. Both are descriptions of how a particular form behaves, not a ranking of which form is better.
How Bark Mulch Settles Over Time
Pine bark settles slowly. One study by UF/IFAS found it maintained two-thirds of its original depth after two years. That is one study's observation of how the material settled over that period — not a service life, and not a schedule for replacing or topping up a bed. It describes a proportion of the original layer still present and the time that had passed; it says nothing about how deep a layer should be to begin with, and it is not a basis for comparing bark against any other mulch material.
What This Page Does Not Cover
This page describes bark mulch as a material and deliberately stops there. It does not work out how much you need for a bed or a project — that is the mulch calculator's job. And it does not provide a general coverage or depth reference, which the mulch coverage chart covers.
Sources
The material descriptions on this page are based on the following sources.
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