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.
California native vines
These aren't widely available, so you'll likely need to go to a specialist nursery or plant sale to find these. These are listed alphabetically by genus, and I've indicated if it's deciduous or evergreen. These will all grow through a fence or other support and don't need to be tied.
Not a bee plant, but a larval food source for the native California pipevine swallowtail butterfly. The unusual flowers are attractive to flies and appear in early spring before the leaves. Native to riparian areas in northern California and southern Oregon, it will need regular water and part shade in the garden, although it can subsist on less water but will go dormant in the summer. This plant reaches up to 15 feet and can cover a fence or grow up through a tree.
California morning glory (Calystegia purpurata ssp. purpurata). Deciduous to semi-deciduous. Sunset zones 14-24.
California honeysuckle (Lonicera hispidula). Evergreen. Sunset zones 7-9, 14-24.
This plant is used as either a vine or a groundcover. It differs from the more commonly sold non-native honeysuckles in that the pink and white flowers are more subtle and not fragrant. This spring-bloomer is attractive to many bees -- including honey bees, carpenter bees, and bumble bees -- and is also used by hummingbirds. Grow this low-water plant where the roots will be shaded but the foliage will be in sun. Looks best with a few deep waterings over the summer.
These are more commonly available than the natives listed above and add additional bloom time and interest to the garden.
Purple lilac vine (Hardenbergia violacea) 'Happy Wanderer'. Evergreen. Sunset zones 8-24.
This Australian native blooms in late winter and early spring. It needs moderate water and full sun, and will need to be tied or otherwise supported as it begins to grow. Thin the stems after blooming to prevent it from becoming too tangled. The small purple flowers are attractive to honey bees.
Passion vine (Passiflora cultivars). Evergreen to semi-deciduous. Sunset zones 5-9, 12-24.
These vigorous South American natives will grow quickly to cover a fence or pergola in one season. Due to this growth habit it has become invasive in Hawaii. While the leaves can look a bit tattered by late summer, the flowers put on a spectacular show. It's the larval food source for the gulf fritillary butterfly, so it brings the colorful non-native adult butterfly to the garden. This vine will need to be tied to a sturdy structure to get it going, but once it starts it will provide fast cover. It needs regular water and full sun to light shade. There are many cultivars available with flowers in varying colors from blue to white. In addition to honey bees, we routinely see carpenter bees using this plant at the Haven.
Wisteria (Wisteria sinensis). Deciduous. Sunset zones 3-24.
Next to star jasmine, this very vigorous grower might be the most commonly used vine in the Sacramento region. Just be prepared to give it a very sturdy structure! This Chinese native needs only moderate water and full sun. We grow the cultivar 'Cooke's Purple' at the Haven, as it re-blooms (although not as spectacularly) in July. It is used by larger bees like carpenter bees and bumble bees.
This plant has become invasive in the southeastern US, where the more restrained native Wisteria frutescens is a better choice.
It's that time of year: hurricane-force winds one day and beautiful spring weather the next. Here's what's happening in the Haven in March:
We've finished our winter pruning and are eagerly awaiting the flowers that will follow. Our winter-blooming plants are going strong, providing vital food for the honey bees at the Laidlaw Honey Bee Research Facility next to the Haven. Some top winter-blooming plants for bees include rosemary (Salvia rosmarinus -- yes, rosemary is now a salvia!), germander (Teucrium fruticans),
Our irrigation system is always given a going-over in the winter to ensure there are no leaks and that the precious water is being used as efficiently as our system will permit. We'll be working on this throughout March.
This is the start of the time when the Haven changes almost weekly. If you're planning a visit, things really get going in late March, and the garden remains at its best through the end of May. Thanks to a generous donor, we had the funds to replant one of our display beds this winter. We'll be using additional support from our Crowdfund campaign to refresh our demonstration orchard.
If you'd like to plan your own bee garden, you'll find a searchable plant list on our website. The list includes bloom time, bee resources provided, Sunset growing zones, and water and light requirements. In addition to our full plant list, you'll find several targeted (e.g. low-water, shade, etc.) bee plant lists here.
Yolo County has moved into a lower COVID tier, and we hope to resume guided tours by the last week of March. Pending approval by the University and COVID restrictions on group size, we look forward to welcoming tours back to the Haven. The garden remains open for individual visitors.
In the meantime, we've loaded more videos to our YouTube channel; look for more throughout March.
Thanks to everyone who donated, shared, or otherwise supported our February fundraising effort through Crowdfund UC Davis. We've nearly reached our goal of $2500. Contributions may be made here through February 28. Thank you!/div>/div>/div>
Our understanding of Russian sage's native habitat remains unchanged. It's still not from Russia, but is native to grassland areas in western China, Pakistan, and Afghanistan. These hot, dry, sunny areas have summer weather similar to California's Central Valley so it does well in our gardens.
Here are links to some of the scientific papers describing these changes for those who wish to learn more:
Salvia yangii. National Center for Biotechnology Information. Link here.
Taxon. 2017. Salvia united: The greatest good for the greatest number. Read here.
American Journal of Botany. 2012. Phylogenetics, biogeography, and staminal evolution in the tribe Mentheae (Lamiaceae). Read here.
Please consider supporting our Crowdfund UC Davis campaign. We rely on donations and grants to keep the Haven and this blog going to share accurate, science-based information about bees and gardens. Thank you!
It's unlikely we'll be able to resume in-person programs in 2021, but we've got lots of virtual programming planned, and hope to resume limited guided tours when we get University approval. In the meantime, February events include:
February 9, 12:15 to 12:45pm. Bee Garden Q&A. Take a lunch break and join us for this bee garden question and answer Zoom class. Free, no registration required. We'll start with a quick look at what's blooming and buzzing in the Haven and then open it up for any questions about bees and plants. Meeting ID: 966 3997 6701 Passcode: 202584.
February 15, 10:00am. Making a Solitary Bee House and Bee Diversity. Two new videos will go live on our YouTube channel as part of UC Davis Biodiversity Month. This virtual event replaces the annual Biodiversity Museum Day, normally held the Saturday of President's Day weekend.
February 23, 12:15 to 12:45pm. Bee Garden Q&A. Take a lunch break and join us for this bee garden question and answer Zoom class. Free, no registration required. We'll start with a quick look at what's blooming and buzzing in the Haven and then open it up for any questions about bees and plants. Meeting ID: 995 0184 7681 Passcode: 672621.
Additional events will be posted on our webpage as they are scheduled.