This argument has raged between us and our landscape architect friends for several years, and we will, no doubt, continue to have this spirited debate long into the future.
We disallow wood chip mulch on all of our commercial projects with parking garages. Many qualities of wood chips recommend their use. Wood chip mulch looks better than rock mulch. The organic material of wood chip mulch cools the root ball of the plant and retains the moisture in the ground considerably better than rock. Rock mulch acts as a heat sink, a small sauna, which cooks the root ball during the daytime temperatures and simmers the plant throughout the evening. But, WOOD CHIPS FLOAT…
Despite the all caps above, I cannot stress enough the flaw which this constitutes. During torrential rainstorms, when the rainwater falls at high volumes, the wood chips will float, migrating over the concrete curbing away from the plants they are meant to protect. They collect in the gutters and sewer drains, beginning their journey to a better place. Unfortunately for our nomadic wood chips, they never make it to the nature preserve. They are waylaid at the storm system catch basin (usually at the bottom of garage’s driveway). There the wood chips congregate with their brethren until they have completely blocked the catch basin, and, surprise, we have a small lake! This lake eventually makes its way under the parking garage door and begins to flood the underground parking garage.
This scenario may seem fanciful, but we learned this lesson the hard way, twice. Both buildings had underground parking garages and both experienced 100 year flood events within weeks of their grand openings. Both were landscaped with wood chips, and both wound up with flooded garages.
So, until someone invents a mulch that will not float away, we will continue to advise our clients to invest in rock mulch.