- Author: Christine Casey
Bee gardeners are good stewards of the environment, which includes making the most of our precious water supplies in the garden. But are you getting the most Bees Per Gallon? We've recently completed a five-year study to evaluate the bee-attractiveness of common northern California landscape plants. Funded by the USDA-NIFA-SCRI, this work was part of a US-wide project to investigate how the horticulture industry can support bees. At UC Davis, we evaluated low- and medium-water plants that do well in northern California.
While all the plants we tested were bee-attractive to varying degrees, here are the ten most-attractive plants with WUCOLS ratings of L or VL in the Central Valley region. These are the plants that will help your garden support the most bees with the least water -- the most Bees Per Gallon!
This list is not intended to be a comprehensive recommendation. There are other great low-water bee plants (here's a list on the Haven's website); the most detailed recommendation for California bee plants of all water needs is in California Bees and Blooms by Heyday Press.
Yarrow (Achillea millefolium 'Moonshine' and 'Island Pink')
Full sun
WUCOLS rating for the Central Valley = L
Blooms summer and fall
Grows approximately 2ft h x 2ft w
Sunset zones 1-24
Cape balsam (Bulbine frutescens)
Full sun
WUCOLS rating for the Central Valley = L
Blooms nearly year-round
Grows approximately 2ft h x 3ft w
Sunset zones 8, 9, 12-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms late winter
Grows approximately 1ft h x 4ft w
Sunset zones 5-9,14-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms nearly year-round
Grows approximately 3ft h x 3ft w
Sunset zones 8, 9, 12-24
Full sun
WUCOLS rating for the Central Valley = VL
Blooms summer and fall
Grows approximately 3ft h x 3ft w
Sunset zones 7, 9, 12-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms summer
Grows approximately 2ft h x 2ft w
Sunset zones 2B-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms late summer
Grows approximately 4ft h x 4ft w to 8ft h x 8ft w depending on variety
Sunset zones 7-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms summer and fall
Grows approximately 2ft h x 2ft w
Sunset zones 1-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms summer and fall
Grows approximately 2ft h x 2ft w to 6ft h x 6ft w depending on variety
Sunset zones 2-24
Full sun
WUCOLS rating for the Central Valley = L
Blooms summer
Grows approximately 1ft h x 2ft w
Sunset zones 2-24
- Author: Christine Casey
- Author: Lea Corkidi
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.
References
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.