Bark Mulch Density

• Bark tends to be more dense than wood and straw, but its density depends largely on the size of the particles. Density is a factor of a weight/volume ratio, so finer particles make for a denser substance, as more particles can fit into a smaller area. Coarse, uneven bark avoids compression, so it is less dense. Particles of medium-textured bark might range from 8 to 35 mm in size, while fine-textured bark particles can be smaller. Pine bark nuggets, on the other hand, tend to be coarser in texture and are less dense.
  
  

Applying Bark Mulches

• Unlike mulch materials of a lower density, bark mulches should be applied no deeper than 2 to 3 inches. The fine particles, if applied too thickly, can prevent oxygen from reaching plant roots. Coarser bark mulches, such as pine nuggets, can go down to a slightly deeper 4 inches. Bark is useful as a mulch because it is slow to decompose, and need only be reapplied every two to four years. Add mulch to the soil around plant roots to retain soil moisture and protect from insect attack. Applying mulch to the entire garden bed will help prevent weed infestation.
  
  

Benefits of Bark Mulches

• Bark and other wood-based mulches are ideal for preventing weeds because seeds have trouble germinating in them. Bark releases tannins and phenols, which prevent weed growth. Many growers consider bark to be more attractive as a mulch than artificial mulches or straw mulches, and it is often applied to enhance the appearance of a garden. The medium density of bark mulches helps conserve moisture even with shallow applications, although they also tend to be more expensive than other materials. The best plants for bark mulches are fruits, perennials, trees and shrubs.
  
  

Types of Wood Mulch

• Wood chip mulches function similarly to bark mulches but can alter the carbon-to-nitrogen ratio in soil, so application of nitrogen fertilizer may be necessary. Pine bark mulches are dark-colored and come in a variety of particle sizes and densities. Large pine nuggets can float in water, so they may not be ideal where heavy rain is commonplace. Sawdust density is comparable to bark density. This type of mulch should be applied in smaller layers if particles are fine, or in thicker layers if particles are large and coarse.