Mulch can be a very effective way of controlling weeds, but organic forms of mulch also can be ideal places for pests to live and breed. When organic mulch is placed too close to your house, it can provide pests with hidden opportunities to make their way into your home. Following is information about the different forms of mulch, why some can be a problem, and how to prevent that.
Forms of Mulch
Mulches come in two forms – organic and inorganic:
- Organic mulch could be leaves, wood chips, tree bark, compost, pine needles, or a multitude of other such materials derived from plants.
- Inorganic mulch may be natural materials such as gravel, pebbles, stone, or crushed or volcanic rock; it can consist of man-made materials such as ground or pulverized tires, solid sheets of fabric or plastic; it can be made up of other non-plant material.
The purposes and benefits of mulch – organic or inorganic – are its ability to:
- Control weeds.
- Improve water retention for desired plants.
- Provide insulation to regulate soil temperature and moisture.
- Prevent soil erosion.
Organic mulches, in particular, are beneficial in:
- Increasing the moisture content of the soil by reducing or slowing evaporation.
- Helping “feed” the quality and fertility of the soil as it decomposes.
Organic vs. Non-Organic Mulch
Although organic mulches can provide benefits that inorganic mulches do not, it is these same beneficial characteristics that provide negative aspects, because they often attract and provide harborage for insects such as termites, sowbugs, pillbugs, millipedes, earwigs, and centipedes, as well as some ants. Some of the mulches can even provide harborage for some cockroaches and rodents, and provide food for termites. Interestingly, even the color of the mulch that is used can make a difference in its attraction to pests. (See Mulch Color Can Impact Insect Control for more information.)
Because of this, it is important that organic mulch not be laid near the foundation of the home. Rather a “free zone” of at least six inches should be maintained. While it is best to leave this zone bare, it can be filled in with small amounts of non-organic mulches (gravel, stone, rock, etc.) for aesthetic landscaping. It is also important that the ground is graded away from the foundation of the home (or any building) before placing any mulch. This enables water to run off away from the structure instead of toward it.
Another difference between organic and non-organic mulches are their longevity. Because organic mulches do decompose to benefit the soil, this also means that they will not last as long and need to be replaced more often. While non-organic mulches do not provide the soil-nutrient benefits of organic mulches, they will last longer because they do not break down. Additionally, non-organic mulches are much less likely to attract above-ground pests, though their insulation of the soil can still create harborage areas for below-ground pests (such as termites).
A good tip for the use of mulch is never to layer it more than three inches deep. This is true whether you are laying organic or inorganic mulch, but it is especially important for organic mulch. Anything beyond about three inches may never dry out and cause too much moisture in the soil. However, you don't want the layer to be too shallow, or you will defeat the purpose of its use. You would likely make it more necessary to first place a plastic or other fabric sheet/cloth before placing the mulch, use an herbicide, or hand-pull any weeds that grow up through the mulch.
In any case, mulch should be used fairly sparingly to prevent termites which may see the mulch as harborage or food. If you have an existing or have had a previous, termite issues, this is especially critical. Although termites aren't really “attracted” to an area, if there are any around the property, they can easily tunnel to the mulch - then beneath and into the wood of your home - to build out their colonies. Because both organic and non-organic mulches cause moisture retention, which the termites also seek, both can be an issue – and should never be laid as to contact any wood of the home or other structure.