If you’ve participated in a Bay Friendly Landscape Certification program in recent years, you’ve undoubtedly heard my mantra: Mulch! Mulch! Mulch! And, you’ve heard it for good reasons. Numerous scientific studies have reported on the benefits of using mulch in the landscape – particularly organic mulches like wood chips and compost – to control erosion, suppress weeds, retain soil moisture, and moderate soil surface temperature.
Such unbridled passion for mulching has, however, raised the ire of entomologists like UC Berkeley professor Gordon Frankie who believe that ground-nesting bees have unfairly gotten the heave-ho from urban gardens due to “Mulch Madness.”
Frankie argues that 60-70% of the 1,500 native California bee species are into digging not hives. Digging bees need open patches of soil, preferably in proximity to the plants they pollinate. If a female in search of a nesting site finds herself thwarted by a blanket of mulch she’ll buzz off for better digging. As a result, your plants don’t get pollinated and biodiversity in your backyard takes a nose dive. Covering every inch of exposed earth with a thick layer of mulch, Frankie contends, is tantamount to an all out assault against our forgotten soil-dwelling pollinator friends.
You don’t need to do it, and you shouldn’t!
Image by R. Coville, Urban Bee Gardens
Having had the unique opportunity to work with UCSB professor emeritus (Natural History) Adrian Wenner on bee research he was conducting for The Nature Conservancy on Santa Cruz Island in the 1990s, I wholeheartedly agree that Bay Friendly Landscaping should include Bee Wise mulching.
My bee mentor: Adrian Wenner
My yard is dominated by the presence of native bees. They utilize strategically placed pots of soil that I have “planted” near rocks on sun-facing slopes, mulch-free areas at the base of plantings, and open patches lightly top-dressed with less than an inch of high quality compost. (I’ve observed that the bees actually use the compost in nest construction.) I use this combination to provide a variety of habitats for ground-nesting pollinators while also maintaining the benefits of organic mulch use in my landscape.
Image by Beth Muramoto
Providing habitat for native bees isn’t complicated or costly. You just need to “bee” more mindful. So spread the buzz and incorporate the following Bee Wise mulching practices into your Bay Friendly landscape.
1. Plant attractive native California plants rather than ornamentals and exotics. For a list of Bee-Friendly plants visit the Urban Bee Gardens website: http://nature.berkeley.edu/urbanbeegardens/gbt.html
2. Maintain a mulch-free zone of 6 to 12 inches around the base of plants. This will enable ground dwelling bees to construct a nest in proximity to plants being pollinated.
3. Maintain a few small open patches of soil between planting beds to provide habitat for ground-dwelling bees, or install 8-10 inch buried pots of soil that can utilized by nesting bees in mulched areas.
4. Maintain patches thinly top-dressed with less than one inch of compost. This will provide a habitat opportunity for some digging bees while also offering some of the benefits associated with mulch.
5. Remove all evidence of what Frankie calls, “Black Plastic Insanity” aka plastic mulch (of any color). Plastic is not only detrimental to digging bees, it also suffocates soil. Think about it, how long would you survive if shrink-wrapped? Get rid of the stuff! Let the soil breathe. It does, you know.
6. Take all of your nasty garden chemicals and dispose of them once and for all at your community hazardous waste disposal facility. Don’t forget to include those stashes of Lindane and Chlordane that you’ve hidden away for years. I know that they’re out there! Oh, while you’re at it, take all of the chemical fertilizers for the disposal too. Clean your shed of garden dread!
7. Consult these Bee-Friendly resources for additional information.
UC Berkeley, Urban Bee Project
Pacific Horticulture, Garden Allies: Solitary Bees, April 2010
Now get our there garden, and bee happy!