Like all organic mulches, cypress mulch is made from the tree's wood and bark. Properly applied to the soil, cypress mulch will retain soil moisture, regulate soil temperature, and limit soil erosion. Cypress mulch marketers, however, add an additional benefit to their list of selling points. They claim the mulch is one of the gardener's best weapons against termites. The accuracy of that claim deserves examination.
Using cypress mulch may actually attract termites to your yard instead of repelling them, cautions University of Kentucky Extension entomologist Mike Potter. The very reasons you use mulch--to keep your soil moist and protected from extreme temperatures--are the reasons that subterranean termites like it. These insects of the world's tropical and temperate zones play a major role in ridding forests of decaying trees. When those aren't available, they eat other wood, including mulches. University of Florida professor Mary L. Duryea reports that some tests, subterranean termites have survived by eating cypress sapwood and cypress mulch made from sapwood.
Heartwood vs. Sapwood
Cypress trees earned a reputation as termite repellents when old-growth trees were the main source of cypress lumber. Because cypress grows so slowly, trees take hundreds of years to develop decay and insect-resistant heartwood, and their lumber is far too valuable for processing as mulch. Almost all cypress mulch comes from immature trees. It has no more termite resistance than other wood mulches.
Cypress Mulch Use Consequences
The cypress swamps of the American South are losing thousands of acres of trees to the mulching industry each year, according to the Suncoast Native Plant Society Website. What used to be a mere by product of cypress lumber manufacturing has now become a lucrative commercial enterprise, partly because of cypress mulch's claimed termite resistance. Because the cypresses are notoriously difficult to cultivate from seed, replanting seldom occurs. Wildlife habitat is lost, and invasive plants often overrun the swamps.
Gardeners concerned about termites can spare themselves some anxiety and the environment some damage by choosing mulches other than cypress. One solution to both problems is the invasive melaleuca tree now thriving in Florida's Everglades. This tree produces extremely durable and termite-resistant mulch. Mulch from plantation-grown eucalyptus trees is a second resistant and environmentally friendly option.
Applying Cypress Mulch
Never layer cypress mulch more than 3 inches deep, advises Potter. Keep the mulch well away from wooden structures and siding. Piling it around them is an open invitation to a termite home invasion. Because dry cypress mulch repels water, it often washes away in a heavy rain. This limits its usefulness for slope erosion control.