The only scientific study of the role of mulch in gardens was done by a group at UC Santa Cruz as part of a larger study looking at various garden factors and their influence on bee populations. They found a negative correlation between the area of a garden with mulch cover and the number of bee species (Quistberg et al., Environmental Entomology. 2016, 45(3):592-601).
Of course this doesn't mean you shouldn't use mulch, given its benefits. Here are tips on using mulch while also conserving bee habitat:
- The bare area does not need to be large or visible. For example, a bare strip can be left along the side or back of a garage or between larger shrubs that will hide the area. It's also a good idea to not place mulch directly against tree trunks, which will also leave some bare soil.
- In most of California, ground-nesting bees will be finished their seasonal activity by the end of October. If an area needs to be mulched, delay until then. The new bees should be able to emerge from underneath the mulch the following spring.
- Soil doesn't need to be amended in any way to help bees nest. These bees are native to the area and are adapted to excavate nests in hard, crusty summer soil.
- Some bee species nest along fence rows or other straight lines. They can also prefer to create nests in the shade of stones such as these along a path border.
Some other mulch tips:
- If you see wasps in your mulch pile, it has probably been sitting a while and is starting to ferment, creating alcohol and sugars. This happens due to lack of oxygen. Turn the mulch pile and let it sit a few days before using it.
- Avoid colored mulch. The effect of the dyes in these products on bees in unknown.
- Do not use cocoa bark mulch if you have dogs. It can be poisonous.
- Don't overdo it. An inch or two is plenty.
I've had several questions recently about the Bambeco solitary bee house sold at Costco (they sell the Swiss Alps model), so I decided to head to my local store to check it out. While the price is amazing, the house has a few features that are not so ideal. For details on what makes a good solitary bee house, see here and here.
The depth. At 4.5 inches deep, it is sufficiently deep to allow the production of female and male bees.
What's not so good:
The nesting tube diameter. While the variety of diameters is good, solitary bees need tubes from 3/16 to 5/16 in diameter. While other arthropods, such as spiders, may use the larger tubes, they will not be used by bees.
Limited protected overhang. The nesting tubes should be placed so that the entrance has a bit of protection. That's why we make our houses at least an inch longer than the tubes.
The nesting tubes are glued in place. Once a tube is used it should be replaced to help prevent the build up of pathogens.
March 13, 2019: winter update
The bee house is not holding up well to the winter weather. Here's a photo showing some superficial mold as well as separation of the sides from the base. Note that I added extra protection by attached redwood fence boards to increase the cover of the roof.
March 27, 2019: comments on the 2019 model
Update July 1, 2019
Update October 7, 2019
I have discarded the 2019 bee house. The paint continued to peel and the wood on the roof started to split. I removed the wooden blocks in the front of the house and will use these next year. For folks who have been asking what a correctly designed bee house looks like, here is an example of the one we sell at the Haven.
What makes it correct:
1. It's made out of redwood; studies have shown that bees prefer to nest in wood.
2. The depth and diameter of the nesting tubes are correct. The holes are drilled 5 inches deep, and the openings range from 3/16 to 5/16 inch in diameter.
3. Paper straws have been inserted into the 1/4 inch diameter holes (this is the only size straw available). This means that the tube can be cleaned out after use. I suggest plugging the others with wood filler after use so that they are not re-used.
4. The front of the block has a pattern to it. This may help the bees recognize their individual nest entrance. There is also evidence that a blue front is more attractive to one of the mason bee species.
5. The block has a piece of burlap shading the entrance. Bees are more likely to use the blocks if the entrance is shaded.
My last post covered the use of color in garden design from the perspective of what bees see. While aesthetics are important in any garden, the needs of bees come first at the Haven and other bee gardens. Here are a few examples of color combinations that are attractive to us and provide both pollen and nectar for bees.
Shades of purple throughout the year
As was mentioned in my last post, purple is a color that bees see well. Here are some ideas for shades of purple throughout the year:
Winter: rosemary (nectar), germander (nectar), ceanothus (pollen and nectar), phacelia (pollen and nectar)
Spring:ceanothus (pollen and nectar)
Summer: sages (nectar), Russian sage (nectar), zinnia (pollen and nectar), cosmos (pollen and nectar)
Fall: aster (pollen and nectar), bluebeard (pollen and nectar)
Shades of yellow throughout the year
As a complementary color to purple, yellow is attractive against any of the plants listed above. Some yellow flower choices include:
Winter:bidens (pollen and nectar), blanketflower (pollen and nectar)
Spring:bidens (pollen and nectar), blanketflower (pollen and nectar), lupine (pollen and nectar)
Summer: sage (nectar), sunflower (pollen and nectar)
Fall: sunflower (pollen and nectar)
Spring: Santa Barbara daisy(pollen and nectar), buckbrush (pollen and nectar)
Summer: Santa Barbara daisy (pollen and nectar), gaura (pollen), veronica (pollen), coneflower (pollen and nectar), zinnia (pollen and nectar), cosmos (pollen and nectar), California buckwheat (pollen and nectar)
Fall:gaura (pollen), California buckwheat (pollen and nectar)
Hot colors throughout the year
Winter: California poppy (pollen), Cape balsam (pollen and nectar)
Spring: Cape balsam (pollen and nectar), sage (nectar)
Summer: Cape balsam (pollen and nectar), coneflower (pollen and nectar)
Fall: Cape balsam (pollen and nectar), sage (nectar), sedum (pollen and nectar)