Good horticultural practices are important to the success of any garden. In bee gardens, though, we need to do things a bit differently, as some common practices may not be best for the bees. When most of us think of bees and pollination the managed European honey bee, Apis mellifera, comes to mind. But beyond the honey bee are over 1500 species of bees native to California, many of which provide essential pollination services in both wild and agricultural settings. About 70% of these wild bees live in underground nests. This includes the social bumble bees and solitary bees like the long-horned bees (Melissodes spp.), digger bees (Anthophora spp.) and sunflower bees (Svastra obliqua) that are common in urban gardens.
Three important practices that should be adjusted to accommodate ground-nesting bee habitat are mulching, tillage, and sanitation.
Mulch has many benefits in the garden. It retains soil moisture, can protect against soil temperature extremes, and provides valuable habitat for arthropod predators such as ground beetles (family Carabidae). Ground-nesting bees need bare soil to create their nests, however, so bee gardeners should leave some ground uncovered. Visitors to the Honey Bee Haven will notice that the garden has many areas of sparsely-laid mulch to accomplish this. Turf-covered areas are not used for nesting.
Ground-nesting bees have soil preferences that vary by species. This is an area in which very little research has been done, but we do know that undisturbed soil is essential. Tilling the garden destroys underground bee nests and disrupts abandoned rodent burrows that are important bumble bee nesting sites.
Finally, while sanitation is an essential tactic in garden pest management, it’s important to not be too neat. Small clumps of grass or weeds or debris left under shrubs can protect the bumble bee queen as she overwinters in her nest below. Garden visitors will see that we leave some weed growth on the garden edges to provide this type of habitat.