Does Mulch Attract Termites?

Homeowners often express concern that mulch applied to plants in the landscape may attract or harbor termites, which may then infest their homes. Duryea and others have documented that subterranean termites are capable of consuming certain types of mulch, including pine bark, pine straw, ground yard waste and cypress mulch. Also, the warm, moist conditions found under mulch tend to be favorable for termite exploration, tunneling and feeding. However, in a recent study (Long, et. al.) at University of Maryland, mulch-fed termites survived poorly compared to those consuming white birch wood (a termite delicacy). In the field, sustained termite activity was actually higher under pea gravel mulch than under pine bark, eucalyptus, and hardwood bark mulch. Based on their results, the authors recommend that thick layers of mulch (including rock) be kept 18 inches from structures. Thinner layers can be placed near, but not touching building foundations.

An interesting finding in Duryea’s study was that, while the heartwood (the dark-colored core of the trunk) of cypress was consumed by termites much less than pine sapwood (termite candy), the sapwood of cypress was nearly as palatable to the termites as pine sapwood. Both heartwood and sapwood of Melaleuca (an invasive tree species in Florida) were consumed much less than pine wood (see http://edis.ifas.ufl.edu/BODY_FR075 ).

The general consensus among researchers seems to be that organic mulches create favorable termite habitat, and, while most commonly used mulches are low quality termite food sources, termites do consume them to some extent. Although there is no evidence that mulches "attract" termites, they do create favorable conditions for termites near the home. The most important practice for detecting a termite infestation in one’s home is to leave at least a foot of concrete foundation exposed so that mud termite tunnels can be easily seen during inspection.

References:
Duryea, M.L. J.B. Huffman, R.J. English and E.G. McPherson. 1999. Will subterranean termites consume landscape mulches? Jour. Arbor. 25:143-150.

Long, C.E., B.L. Thorne, N.L. Breisch and L.W. Douglass. 2001. Effect of organic and inorganic landscape mulches on subterranean termite (Isoptera: Rhinotermitidae) foraging activity. Physiological and Chemical Ecology. 30:832-836.

Chris Starbuck, Woody Ornamental Horticulture, UMC (573)882-9630