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

 

 

 

 

California lilac (Ceanothus maritimus 'Valley Violet'). All California lilacs are attractive to bees, but this variety grows well in the Sacramento region.

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

 

 

 

Santa Barbara daisy, Mexican fleabane (Erigeron karvinskianus)

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

 

 

 

 

California buckwheat (Eriogonum fasciculatum)

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

 

 

 

 

Gaura (Gaura lindheimerii)

Full sun

WUCOLS rating for the Central Valley = L

Blooms summer

Grows approximately 2ft h x 2ft w

Sunset zones 2B-24

 

 

 

 

Texas ranger, Texas sage (Leucophyllum frutescens)

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

 

 

 

 

Catmint (Nepeta x faasenii 'Walker's Low'). We tested this cultivar, but others are also bee-attractive.

Full sun

WUCOLS rating for the Central Valley = L

Blooms summer and fall

Grows approximately 2ft h x 2ft w

Sunset zones 1-24

 

 

 

 

Russian sage (Salvia yangii (Perovskia atriplicifolia))

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

 

 

 

 

Wall germander (Teucrium x lucidrys (Teucrium chamaedrys))

Full sun

WUCOLS rating for the Central Valley = L

Blooms summer

Grows approximately 1ft h x 2ft w

Sunset zones 2-24

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.

 

Russian sage (Salvia yangii) and prairie coneflower (Ratibida columnifera)

With apologies to grammarians everywhere, the mulch/bee dilemma is a question I often receive. Many bee gardeners know that 70 percent of California native bees nest underground, and that access to bare soil is needed for nest building. But what about the benefits of mulch? It helps retain water, serves as habitat for ground-dwelling insects such as the beneficial ground beetle, and breaks down to add nutrients to the soil.

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.

Bare soil can be left between mature shrubs to provide bee nesting habitat

• 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. 

Close up of ground-nesting bee nest entrances shown to the left. Notice that there is some mulch and other debris in the soil: it doesn't need to be completely free of other material.

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.

Gardeners are always looking for ways to add more plants, especially in a small garden. One way to do this (and in hot California add some much-needed shaded seating) is with a pergola. And what better way to cover it than with vines that will bring in the bees and butterflies? Here are some suggestions:

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.

California pipevine (Aristolochia californica). Deciduous. Sunset zones 5-10, 14-24.

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.

This vigorous grower will quickly cover a fence or unsightly building. The large pink flowers are present from spring to mid-summer, and this plant benefits from removal of older woody growth in the winter. It needs moderate water and full sun. Think carefully when you site this plant as it can easily take over.

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.

California honeysuckle blooms in spring

Bird's nest made from California honeysuckle

 

Non-native vines

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.

Gulf fritillary caterpillars consuming passion vine leaves

Adult gulf fritillary on verbena

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.

Wisteria blooms in spring with highly fragrant flowers