Cypress trees take as much as a century to reach maturity and when harvested, it is very unlikely to be replaced by a new, healthy tree. Since mature cypress trees have been logged at unsustainable levels, cypress mulch now most often comes from immature trees which have not yet developed the rot and insect-repellent qualities valued by gardeners, according to Lisa Swann of the NWF. This means that most cypress mulch is simply wood chips that do not contain the rot and insect-repellent or durability that gardeners want. Further, beneficial garden mulch should contain an even mix of carbon-rich and nitrogen-rich materials. Because wood chips and bark are virtually all carbon, they tie up the available nitrogen in the soil as they decompose, leaving plants without the nutrients they need to grow.

The most nutritious garden mulch is something most gardeners already have on hand: yard waste. Researchers at the Ohio Agricultural Research Center found that composted yard waste (a mix of kitchen scraps and yard trimmings) increased the number of flowers on rhododendron plants by 300 percent over plants grown without mulch. Wood mulch gave no such benefit.

When buying mulch, read the packaging carefully to see what material it is made from, and resist buying any products made from cypress. You’ll be helping to protect our nation’s wildlife heritage.