- Author: Christine Casey
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.
Plant all three this fall for a show next summer!
- Author: Christine Casey
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.
Wild onion
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.
Mustard
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.
Oxalis
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!
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- 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
Conserving water and helping bees are goals shared by many gardeners. Given California's current extreme to exceptional drought status, it's time to re-visit the best low water plants for bees. Haven scientists are nearing the end of a long-term project examining bee preference for commonly used landscape plants. We've focused on low-water plants for northern California, while our San Diego-based colleagues have focused on southern California plants.
One of the consistently most-preferred plants has been Russian sage, Salvia yangii, formerly Perovskia atriplicifolia (read about its reclassification here). It's been either the first, second, or third most attractive plants to honey bees, and second, third, and sixth most attractive plant to native bees over the course of our observations.
Native to central Asia, this plant copes well with hot, dry conditions as well as extreme cold. It blooms from late spring to frost, providing a season-long bee resource. Like most members of the Lamiaceae, it serves only as a nectar source. Pair it with a complimentary colored pollen-providing plant in pink or red, like the coneflowers shown here, for both garden interest and bee nutrition.
- Author: Christine Casey
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.