Mulch, Termites, and Your House Foundation

Termites (Isoptera) are a common worry of homeowners. Most people are concerned that a layer of mulch applied next to a house foundation might draw the pests. It is a worry that spawns several different questions. Unhappily, not all experts agree on the answers to all of these questions. But if you wish to use mulch near your foundation and are unsure as to how to proceed, the best short answer is this:

• To be on the safe side, leave a 1-foot-wide swath of ground mulch-free all along your foundation and make sure door and window frames do not touch the mulch. (Also, keep the ground here as dry as you can).
• Outside of this mulch-free zone, apply mulch (as people often do to suppress weeds in their foundation plantings), but limit its depth to just a few inches, and inspect it vigilantly for termites.

Now that you have the short answer, let’s explore this issue in greater depth.

Drainage (Moisture), Termites, and Your Foundation

When it comes to termite control, opinions vary on the degree of caution you must exercise when applying mulch near a house. Mulch itself isn’t a good source of nutrition for termites. In fact, it’s a non-preferred food source. However, mulch provides conditions termites prefer: it retains moisture, which they like, and it insulates them from temperature extremes. It’s extremely rare for termites to be present in bagged mulch brought in from big box stores or from commercial companies, as termites rarely survive the wood shredding process. Instead, termites live in the soil, and then seek out food sources. Mulch simply provides conditions that help them thrive. But when mulching foundation plantings, you should, at the very least, be aware of termite issues, especially if:

• Termites are known to be a concern in your area.
• You, yourself have had trouble with termite pests in the past.

Since termites have the potential to cause a lot of damage, it is best to play it safe and err on the side of caution when mulching near your home’s foundation.

Having good drainage around a foundation is important anyway, but it is particularly important for termite control because termites like moisture. Ensuring adequate drainage is relatively simple: Grade the ground so that it has about a 5-percent slope away from the house to channel water away from the foundation. Make sure gutters are clean and divert water away from the foundation by installing downspouts and splash blocks.

Drawing Termites and Mulching Around Foundations

Consider the sub-questions implied within the overarching question of whether we need to worry that mulching around foundations causes termite problems:

• Should the mulch be allowed to come into contact with the foundation?
• If so, how deep a layer of mulch is acceptable, meaning how close should the mulch be allowed to come to a wooden surface of the house wall?
• Are some types of mulch preferable when it comes to termite control? Does a wood mulch actually draw these pests to a yard, in search of a snack?

Each of these termite-control questions deserves individual treatment.

There is some disagreement over whether mulch should be allowed direct contact with your foundation. Some experts advise against it altogether (you certainly should not allow such contact if a termiticide was applied to the soil along the foundation when your house was built). If you wish to be totally free of worry regarding termites, then this is the correct answer for you.

If you are less paranoid and intend to let mulch come into contact with the cement of your foundation, then limit the depth of the layer of mulch to about two inches (in fact, even if kept further away from the house, a mulch layer in a foundation bed should not be much deeper than this, with four inches being maximum depth). In answering the question of how close to allow mulch to come to the wood on your house wall, Burnett’s Landscaping in Salem, Connecticut (U.S.) recommends “at least eight inches of exposed foundation between the top of the planting bed and the wood sill plate of the house structure.”

When it comes to the best type of mulch to use when termite control is a concern, there is a widespread misconception. Folks assume that, because termites eat wood, only wood mulches present a problem. That is a myth. There is also the separate question of whether, technically speaking, mulch actually draws termites to your land.

The issue is not termites being drawn to a property by the promise of a wood mulch that they can eat, but rather termites that are already present (in the soil) exploiting the mulch as a hiding place, using it as a launching pad to invade your house. Termites like moisture, and all mulches provide that to some degree. In fact, good moisture-retention is one of the hallmarks of the most effective mulches. Your plants enjoy this quality in a mulch, but so do the termites. And remember, even mulches that retain less moisture (such as stone mulches) still furnish pests with a place to hide.

So the issue is not so much that mulch draws termites to a property (they were probably there already), as it is that mulch makes life more comfortable for these pests. And placing mulch near the foundation, specifically, just invites them to rise up out of the soil and search for ways to penetrate your house’s walls. Cypress sapwood, loblolly pine, and slash pine are all favorites of termites.

The good news is that there are actually some kinds of wood mulch that termites dislike:

• Cedar mulch
• Mulch that comes from the heartwood of cypress
• Eucalyptus
• Southern tidewater red cypress
• California redwood
• Melaleuca

It is more accurate to say that termites eat cellulose than to say that they eat wood. Cellulose can be found in the cell walls of the plants that you grow in your garden (not just trees). Consequently, termites give you another reason not to like them: They can damage your landscape plants.

Know What to Look for and Stay Vigilant

Staying on the lookout for termites and responding swiftly when you detect their presence can save you a lot of money. First of all, find out what termites are and what they look like. You may think that they just look like “white ants,” but it is not as simple as that, although termites are comparable in size to some ants.

Termites are social insects, divided within their colonies by castes, and there are many different species. Not all termites look alike. Populations of the pests are far-ranging; there are termites on every continent except Antarctica. But portions of the northern tier of states in the U.S. (Northern Maine, for example) are lucky: Termite populations there are small or non-existent.

Regularly inspect the mulch in foundation plantings to determine if any termites are present. If you find any, contact a reputable professional in the termite-control business immediately.