Mulch Basics

Mulching is one of the easiest things a home owner can do to simultaneously reduce maintenance to improve aesthetics. Mulching prevents weeds from coming up, reduces evaporation, stops erosions, and insulates the soil in summer and winter. According to the Colorado State University Cooperative Extension, mulch reduces evaporation from the soil surface and reduces irrigation needs by up to 50 percent.

Mulches are generally broken into two types, organic and inorganic. Organic mulches include bark, shredded hardwood, straw, salt hay, leaves, and all natural materials that decompose. Inorganic mulches don’t break down and include gravel, pebbles, shredded tires, plastic weed barriers and landscape cloth. Consider all of the options and pros and cons of each material before purchasing. Plastic weed barriers should only be used when absolutely necessary, since they block water percolation and prevent air flow. Gravel and rock mulches have some benefits and disadvantages too. Unlike plastic, gravel allows water to run through; it also lasts for a very long time and rarely needs replacing. Rock mulches are completely fire-proof. A few disadvantages are the extreme weight of gravel, which makes it difficult to transport and apply. Another disadvantage is the heat that rocks can retain and reflect when used in high heat and sun exposure areas.

Organic mulches are the most environmentally friendly. A lot of the wood and bark used for mulches is harvested from managed plantations. Municipal wood chips are also very environmentally because they are locally made from recycled trees and plant material that your neighbors put out for the chipper. Avoid cypress mulches because they are not sustainably harvested and have a negative impact on the natural cypress stands.

There are a number organic mulches available, from beauty bark to pine bark. Beauty bark is made from fir and hemlock bark naturally dyed red, brown, or black. Medium ground beauty bark is the most popular size, generally recognized by the fluffy consistency with some long shards or shavings of wood. Pine Bark nuggets are another very popular mulch. Large chunks of pine bark are slow to decompose and generally last a year or more. Bark nuggets can be bought in different sizes from small to very large. Pine bark is extremely lightweight, which means it will float away in water erosion zones.

When choosing mulch, consider that coarse mulch takes longer to break down and provides a lot of healthy air circulation. On the other hand, fine mulch retains more moisture and is better at maintaining soil temperature and preventing crusts. Finely textured mulches can also suffocate plants, by inhibiting air circulation, if applied too thickly.

Move mulch away from plants that start yellowing or dropping leaves. This could mean air can’t reach the plant’s roots. These symptoms can also be caused by sour mulch that has remained wet for too long and started to grown harmful organisms that cause an imbalanced pH. Raking mulch improves air circulation and eliminates this condition.

Mulch should be applied 2-4 inches thick; no more. Coarse bark nuggets can be added on the thicker side, but fine mulches should be applied more thinly; 2-3 inches max. Avoid piling mulch over the trunks of trees and shrubs. Ideally there should be several inches in each direction around the trunk before mulch begins. Avoid “mulch volcanos” typically seen in parking lot medians where there are tall mounds of mulch piled directly up to and surrounding the trunk. This is exactly what not to do when applying mulch. For best results apply mulch thinly to a broad area.