What Native California Plants Are Best For Attracting Pollinators?

Bug Squad By Kathy Keatley Garvey December 18, 2018

What Native California Plants Are Best For Attracting Pollinators?

That's a question often asked.

Now for answers.

Ola Lundin, first author

Ola Lundin, first author

Neal Williams, professor and Chancellor’s fellow

Neal Williams, professor and Chancellor’s fellow

Kimiora Ward, project scientist (Photos: Kathy Keatley Garvey)

Kimiora Ward, project scientist (Photos: Kathy Keatley Garvey)

Three pollination ecologists from the University of California, Davis, have just published their research, “Identifying Native Plants for Coordinated Habitat Management of Arthropod Pollinators, Herbivores and Natural Enemies,” in the Journal of Applied Ecology. It details what plants proved most attractive to honey bees, wild bees and other pollinators, as well as what drew such natural enemies as predators and parasitic wasps.

“I hope this study can inform selection of plants that support pollinators and natural enemies without enhancing potential pests,” said lead researcher and first author Ola Lundin, a former postdoctoral fellow in the Neal Williams lab, UC Davis Department of Entomology and Nematology and now a postdoctoral fellow in the Department of Ecology, Swedish University of Agricultural Sciences, Uppsala.

He and co-authors Williams, professor of entomology and a Chancellor's Fellow at UC Davis; and project specialist Kimiora Ward of the Williams lab conceived the ideas and developed the methodology for the research project.

“Planting wildflowers is a key strategy promoted nationally to support wild and managed bees,” said Williams. “Successful adoption of these plantings in agricultural landscapes will require that they not only support pollinators but that they also avoid supporting too many pests. Plant selection going forward will need to balance multiple goals of pollinators pest management and other functions. This research is a first step on the path to identifying plants that will meet these goals."

The trio established 43 plant species in a garden experiment on the grounds of the Harry H. Laidlaw Jr. Honey Bee Research Facility at UC Davis. They selected plant species that were drought-tolerant; native to California (except for buckwheat, Fagopyrum esculentum, known to attract natural enemies and widely used in conservation biological control); and, as a group, covered a range of flowering periods throughout the season. (Download the plant species here.)

The Great Valley gumplant (Grindelia camporum) was one of the 43 plants tested. Here a cukoo bee Triepelous Epeolus, forages on a blossom. (Photo by Kathy Keatley Garvey)

The Great Valley gumplant (Grindelia camporum) was one of the 43 plants tested. Here a cukoo bee Triepelous Epeolus, forages on a blossom. (Photo by Kathy Keatley Garvey)

Every week, over a two-year period during the peak bloom of each plant species, they engaged in three different sampling techniques: netting wild bees, observing honey bees, and vacuuming insect herbivores, arthropod predators and parasitic wasps.

“For early season bloom, Great Valley phacelia (Phacelia ciliata) was a real winner in terms of being attractive for both wild bees and honey bees,” Lundin said. “Elegant Clarkia (Clarkia unguiculata) flowers in late spring and was the clearly most attractive plant for honey bees across the dataset. The related Fort Miller Clarkia (C. williamsonii) was also quite attractive for honey bees and had the added benefit that a lot of minute pirate bugs visited the flowers.”

Lundin said that common yarrow (Achillea millefolium)“attracted “attracted the highest numbers of parasitic wasps but also many herbivores, including Lygus bugs.”

“In general a lot of parasitic wasps were found on Asteraceae species (the daisy family) and this was a somewhat surprising result considering that they have narrow corollas, and for parasitic wasps relatively deep corollas that can restrict their direct access to nectar. Under the very dry conditions in late summer, Great Valley gumplant (Grindelia camporum) and Vinegarweed (Trichostema lanceolatum) both performed well and attracted high numbers of wild bees.”

The team found that across plant species, herbivore, predator and parasitic wasp abundances were “positively correlated,” and “honey bee abundance correlated negatively to herbivore abundance.”

The take-home message is that “if you're a gardener or other type of land manager, what you'd likely prefer would be a mix of some of the most promising plant species taking into account their individual attractiveness for these arthropod groups, plus several more factors including costs for seed when planting larger areas,” Lundin said.

“Plant choice can also depend on how you weigh the importance of each arthropod group and whether you are interested in spring, summer or season-long bloom,” Lundin added. Those are some of the questions that the Williams lab plans to explore in future projects.

Phacelia californica was among the 43 plants tested. Here a bumble bee, Bombus vandykei, and a honey bee, Apils melllifera, share a blossom. (Photo by Kathy Keatley Garvey)

Phacelia californica was among the 43 plants tested. Here a bumble bee, Bombus vandykei, and a honey bee, Apils melllifera, share a blossom. (Photo by Kathy Keatley Garvey)

“It was fascinating for me to see how these and other plants flowering in the latter part of the summer not only survived but also seemed to enjoy themselves in the heat without water for months!” Lundin quipped.

Williams praised the “uniquely capable team that came together.”

“Ola is an emerging leader in considering integrated management of pests and pollinators and Kimiora is a known expert in developing regionally-relevant plant materials to support pollinators,” Williams said. “They and some talented UC Davis undergraduates--notably Katherine Borchardt and Anna Britzman--compiled a tremendously useful study.”

The overall aim of the study “was to identify California native plants, and more generally plant traits, suitable for coordinated habitat management of arthropod pollinators, herbivores and natural enemies and promote integrated ecosystem services in agricultural landscapes,” the researchers wrote.

More specifically, they asked:

  1. Which native plants among our candidate set attract the highest abundances of wild bees, honeybees, herbivores, predators, and parasitic wasps,

  2. If the total abundances of arthropods within these functional groups across plant speacies are related to the peak flowering week, floral area, or flower type of the focal plant species, and

  3. If the total abundances of arthropods within these functional groups are correlated to each other across plant species.

“A first critical step for design and implementation of multifunctional plantings that promote beneficial arthropods while controlling insect pests is to identify suitable plant species to use,” the authors wrote in their abstract. “We aimed to identify California native plants and, more generally, plant traits suitable for the coordinated management of pollinators (wild bees and honey bees), insect herbivores and arthropod natural enemies (predators and parasitic wasps).”

At the time, the Laidlaw grounds included nearly 50 bee colonies: some 20 to 40 honey bee colonies, and eight managed research colonies of the yellow-faced bumble bee, Bombus vosnesenkii.

The project drew funding from the USDA Resources Conservation Service, USDA Agricultural Marketing Service, USDA National Institute of Food and Agriculture and a Swedish foundation for scientific research, the Carl Tryggers Stiftelse for Vetenskaplig Forskning.

Phacelia campanularia was one of the 43 plants tested in the UC Davis research garden. Here a honey bee sips nectar from a blossom. (Photo by Kathy Keatley Garvey)

Phacelia campanularia was one of the 43 plants tested in the UC Davis research garden. Here a honey bee sips nectar from a blossom. (Photo by Kathy Keatley Garvey)

These are some of the 43 plants tested in the UC Davis research garden. This is an illustration from the research paper. (Photos by Ola Lundin)   https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=28959

These are some of the 43 plants tested in the UC Davis research garden. This is an illustration from the research paper. (Photos by Ola Lundin)

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=28959

Six Essential Perennial Herbs

Thymus vulgaris

Thymus vulgaris

Get advice on growing and harvesting rosemary, sage, thyme, mint, chives and marjoram.

Perennial herbs are easy to grow and will enhance your garden, and your cooking, year after year. They are easy to grow and need very little looking after and can be grown in beds and borders, or in containers on a patio or balcony.

Discover how to pick herbs.

Giving herbs the right growing conditions helps to ensure they have the best flavour. Plant them in full sun, if possible – this will bring the essential oils to the surface of the leaf, giving a strong flavour. Mint, rosemary and chives will tolerate some shade, but if grown in damp, cold soil, they may suffer over winter.

To keep perennial herbs healthy and productive, pick them regularly. All of the herbs featured here also have edible flowers, so pick those too and enjoy them with salads, in drinks and as a garnish. Once they have finished flowering, cut them back. Cutting back evergreen herbs, like rosemary, helps prevent them becoming woody. Discover more about keeping herbs productive.

Herbaceous herbs, such as mint, which die back over winter then regrow in spring, should be cut back to about 4cm above the soil after flowering. You will then get a second crop of fresh new leaves through to the first frosts.

Discover how to get the best from six perennial herbs.

Perennial herbs are easy to grow and will enhance your garden, and your cooking, year after year.

1 Mint

Mint grows best when it is left to spread naturally. It can be invasive, however, so if this is likely to be an issue, grow it in pots. Growing it in full sun will give it the best flavour, although it will also grow in partial shade. Pick the leaves before flowering or after the plant has been cut back in summer.

Mint Leaves

Mint Leaves

Care

The easiest way to preserve mint is to freeze the leaves, whole or chopped. Mint rust produces small, rusty spots that usually start on the underside of the leaf. Cut back hard and remove any fallen leaves from the soil – the new growth should return clean. If mildew becomes a problem, move the plant to a sunny, airy position. Mint leaf beetle can also be an issue.

2 Rosemary

Evergreen rosemary can be harvested throughout the year. The flowers are also edible, with a light rosemary flavour – delicious in rice dishes. Grow in a warm, sunny site in well drained soil. It will also grow well in a container – use a soil-based compost and pot up annually in the autumn.

Rosemary

Rosemary

Care

To keep it productive and to stop it becoming woody, cut back after flowering. Rosemary beetle may be a problem – the beetle and its larvae feed off the leaves from autumn to spring. To tackle an infestation, place sheets of newspaper under the plant, the tap or shake the branches to knock the critters onto the paper, making them easy to dispose of.

3 Sage

The leaves of culinary sage can also be used all year. The flowers are edible and can be scattered in salads or fruit puddings. Sage leaves can be preserved in oil and butter. Plant in a warm, sunny site in well-drained soil. Sage also grows well in a container – use soil-based compost.

Sage

Sage

Care

Cut back after flowering in summer to encourage new growth and to prevent the plant becoming woody. Sage can be prone to leaf hopper – there is not much you can do about it, except to remove damaged leaves. If plants in pots are affected by mildew, move them to an airier situation and remove the damaged leaves.

4 Thyme

Thyme is evergreen and can be used all year round. It makes lovely oils and butters. Plant in a well drained soil in a sunny spot. Thymes do not like wet winters or sitting in water, so make sure that the soil has adequate drainage. To grow in containers, use a soil-based compost mixed with horticultural grit.

Thyme

Thyme

Care

Cut back after flowering to help plants survive the winter. Thyme rarely suffers from pests, although aphids can attack new growth – spray them with soft horticultural soap.

5 Chives

Cut fresh leaves throughout the growing season, and scatter the pretty flowers over salads – they have a mild onion flavour. Preserve the chopped leaves in butter or freeze in ice cube trays without water. Plant in a well-drained, fertile soil in a sunny position and keep well watered throughout the growing season.

Chives

Chives

Care

Mulch with well-rotted manure in autumn. Chives grow well in containers – use a soil-based compost and pot up annually in the spring, when the new growth appears. Onion fly, downy mildew and rust can be a problem – in mild cases, cut back hard, and in severe cases, dig up and bin the plants, taking care not to plant more members of the allium family in the same spot. Find out how to rejuvenate chives.

6 Oregano / marjoram

Oregano

Oregano

The leaves can be picked nearly all year. Oregano originated in the Mediterranean, so plant in a well-drained soil in a sunny position. It will grow happily in a container, using a soil-based compost that has been mixed with a handful of horticultural grit. Preserve it in butters, oils, or dry some sprigs.

Care

Oregano is fairly free from pests and diseases, but die back or powdery mildew can be a problem if planted in heavy soil or partial shade. There are fewer edible leaves when in flower, so cut back the plant after flowering to promote new growth.

Growing herbs in pots.jpg