For landscaping purposes, there are two types of mulches; Hard Mulch and Soft Mulch. Hard Mulch is stone and is usually a one-time investment. Soft Mulch is usually a wood product that needs to be refreshed or replenished over time. There are also things such as landscaping fabric/weed blocker and groundcover plants that could also be considered mulch since the main purpose of mulch is to retain moisture and block out weeds. I definitely won't deny that landscaping fabric, weed blocker, and groundcover plants have their benefits, but they too bring about their own unique pest issues that I'll try to cover later, for right now let's focus on Hard and Soft Mulches and how they relate to pest issues and pest control.
Hard Mulches come in various shapes and sizes, colors and textures, from lava rocks to river stones. Hard Mulch can be expensive, but it's usually a one-time investment in both money and labor, which is why Hard Mulches are perfect for specific areas and projects such as around foundations and other places where too much moisture could be an issue. Using a 2' wide strip of Hard Mulch (2-4" deep depending on the type) around the foundation of a building can reduce rodent (mice, vole, and shrew) activity next to the building. This is a good thing because voles and shrews spend a lot of time feasting on the bark of shrubs and mice, well they're just busy looking for a way inside to feast on your food. Using the Hard Mulch creates a barrier that tends to discourage rodents from taking up residence near your buildings. Hard Mulches can harbor certain insects such as pill bugs and certain types of ants, so you want to make sure that there is ample clearance between the hard mulch and the siding (16-24" is recommended), in other words the siding shouldn't extend down to the mulch nor should the mulch cover the siding since that tends to create other pest issues. In the situation of buildings that sit on concrete slabs, we don't have that option, but that's not to say we can't landscape. Adding that 2' barrier around the exterior of the building in the form of Hard Mulch will greatly reduce rodent activity near these buildings. There may be an increase in pill bug or ant activity so we'd recommend treating 2' up on the siding and the Hard Mulch to prevent infestations. By using Hard Mulch in this way not only have you cut down on rodent activity but you've also created proper ventilation near the building. This is an important step towards keeping your building healthier!
Soft Mulches come in various shapes, textures, and colors. They are relatively inexpensive, but they require repeat applications over the years to keep them looking "fresh". Soft Mulches decompose over time which makes them very attractive to insects that like decaying things, Carpenter Ants are on this list along with Earwigs, Centipedes, and TERMITES, just to name a few. Soft Mulches should never be used next to buildings for this reason, but are perfect for beds and plantings located away from the buildings. I have seen on countless occasions where Soft Mulch was not only used next to buildings but it was also piled up onto the sides of the building and often over the siding.
I can not stress the degree of wrongness in this type of application of Soft Mulch, nor can I in any way explain how devastated people are when they learn that the landscaping contributed to their pest issues, especially when dealing with Carpenter Ants and Termites. Soft Mulch is an excellent choice to retain moisture around your shrubs, trees and in your beds that are located away from buildings. Creating an environment that encourages wood damaging insects such as Carpenter Ants and Termites in close proximity to any building is a recipe for heartbreak and financial folly since it can render the building unsellable until the infestation is corrected.