Regular Haven visitors notice that we frequently change our planting. It's one of the joys of gardening -- there are always new plants to try and experiment with. At the Haven, research on new plants and methods for bee gardens is essential to our educational mission.
Previous posts have reported on our work with bee plant preferences, with an emphasis on low-water plants. Our colleagues at UC Cooperative Extension in Southern California have done similar work for that part of the state. Previous blog posts have covered research with mulch, plant color, and water; all are important components of a healthy bee garden.
But all this is for naught if it isn't put into practice. So our current work is to create tools for the California horticulture industry to educate employees and customers about bee garden best practices based on this research. The first step in this work is development of an efficient sampling method so growers, landscapers, and public gardens can easily assess the bee-attractiveness of new plants as they come on the market. This will allow these plants to be marketed correctly, and will also help growers to target bee-friendly pest management.
In our attractiveness studies the Southern CA team used timed counts, while the Northern CA team used a snapshot count method (1). This technique consists of 20 second quick counts of every plant that is repeated three times in succession rather than a single 3-minute timed count. The snapshot count is faster to complete and more readily worked into the day of an otherwise busy nursery employee.
The purpose of this study was to calculate the relative net precision (RNP) of each bee counting method at a wholesale nursery (Fallbrook, CA) and a public garden site (Encinitas, CA) in San Diego County. RNP is calculated as shown below and is a way to assess sampling efficiency by balancing precision and sampling cost (2).
RNP = [1/(cost x Rv)] x 100, where Rv = (SE/mean) x 100
Plants in full bloom were sampled weekly for at least 4 weeks using both methods. Bees were counted as honey bees or other bees as this distinction is easy for an untrained observer; only honey bee data is reported here. At both locations, we saw a larger absolute number of bees with the snapshot method, but the trend of most attractive to least attractive was the same for both methods (Figures 1 and 2). We are most interested in this trend rather than the absolute number, which is expected to vary between locations. Additionally, regression analysis shows that the two counting methods are strongly correlated (Figure 3).
Finally, we saw differences between the RNP values calculated for the two sampling methods, with higher RNP for the snapshot method at both locations (Table 1). Higher RNP means greater sampling efficiency (2).
A second year of study will begin in April at additional sites to confirm these findings. We look forward to providing the California green industry with a useful tool for supporting pollinator gardens.
1. Garbuzov and Ratnieks. 2014. Functional Ecology 28: 364-374.
2. Buntin pp 99-115 in Handbook of Sampling Methods for Arthropods in Agriculture. CRC Press, Boca Raton, FL. 1994.
As we move into the hottest, driest part of the summer, many of our gardens are looking a bit worn out. It's certainly easier to stay inside where it's cool and put garden tasks off until the fall.
But the bees are still out there doing their work to bring us food and create habitat for wildlife. What are the plant options for California gardens that will stand up to the heat with little water (all these plants are rated ‘low' in WUCOLS) and be loved by bees?
One great choice is our native California aster, Symphyotrichum chilense. Unlike asters native to the eastern US and Europe, which need regular water in California, this one thrives on low water. Shown here are the cultivars, 'Purple Haze' and 'Point St. George'.
'Purple Haze' is about 2 feet tall, while 'Point St. George' grows low to the ground. The former has deeper purple flowers than in typical for this species. Both need full sun to light shade and will spread (a lot!) to cover an area. Consider yourself warned when choosing an area to plant these in.
In our studies of bee plant preference at UC Davis we found our native aster to be one of the most attractive plants to California native bees. The late summer flowers are a critical source of nectar and pollen at a time when not a lot is blooming.
The flowers age from white to rust in later summer and provide fall color in the garden into winter.
Finally, for intense late summer color, nothing beats California fuchsia, Epilobium canum. There are numerous cultivars available, but my favorite is ‘Catalina', which reaches about 3 feet tall including flowers. California fuchsia will grow in sun or shade but blooms best in full sun. As with the aster, this plant spreads over time, making it a great filler in areas bounded by paths, buildings, or roads. These serve as barriers to keep it contained, while the plant can take the hot conditions often found in these spots.
While California has moved back into drought, the heavy rain we experienced in December has brought on a bumper crop of weeds. The first reaction of many gardeners is to remove them, but I'm asking you to reconsider this to help the bees.
There are common weeds in the Central Valley that provide important nutrients for bees. If possible, leave some weeds behind, especially early in the year when nutrient needs are high and forage may be limited.
Here are a few blooming now to keep in your garden. These will die back once summer heat arrives, so if you're in a fire zone be prepared to remove the dried vegetation once plants are finished flowering.
Allium triquetrum is native to Eurasia and has naturalized in many Mediterranean climates, including ours. California native Allium unifolium will spread quickly to form patches in the garden; both are well-used by bees. To learn more about onions in California, check out this article in Pacific Horticulture.
Those bright yellow fields seen in early spring are often a non-native naturalized mustard. In wild areas this can pose a fire risk as it dries down with summer heat. Mustards, however, have a high-protein pollen that's great for bees. Fortunately many are sold as cover crop seeds that can be managed in the garden. This is one that we grow annually in the Haven -- it goes straight to the compost pile once it's finished blooming, providing nutrients for next year's flowers.
This is Bermuda buttercup, Oxalis pes-caprae. Native to South Africa, it's naturalized in Mediterranean climates worldwide. It spreads by bulb division and is difficult to control.
We don't have his weed at the Haven, but it's in my home garden. I pull much of it, but keep some for the bees. To limit spread, I only allow it to grow in the planting strip between the sidewalk and street. It provides both nectar and pollen, and also contains oxalic acid, a chemical sold commercially for varroa mite control in honey bee hives. Every few years I spread some native wildflower seeds in this spot; the highly bee-attractive Phacelia tanacetifolia has established here. California poppies and native lupines are getting ready to flower as well.
While oxalic acid has been documented to occur in leaves and stems — albeit at concentrations far lower than commercial control products — it's not been looked for in pollen or nectar. Great project for a future scientist!
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>