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

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:

Garden maintenance

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),

many Ceanothus cultivars,

Chaparral currant, Ribes malvaceum 'Dancing Tassels'

chaparral currant (Ribes malvaceum) and

Golden currant, Ribes aureum

golden currant (Ribes aureum). The last three are California natives. Native wildflowers like California poppy (Eschscholzia californica) are also valuable in the bee garden

California native annual wildflowers, such as golden lupine (Lupinus microcarpus densiflorus) and California poppy (Eschscholzia californica) are great March blooming plants for the bee garden. The purple flower is the non-native perennial, tall verbena (Verbena bonariensis).

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Garden irrigation

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.

Garden plantings

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.

 Garden education

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.

Fundraising February

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!

It's the first week of spring at the Haven and our plants are starting to look their best. For those of you who cannot make it to the garden this week, here's a brief tour of what's going on. For those who can make it, I've included some of the bees to look for.

The garden is currently open, although the cities of Davis and Sacramento are now recommending shelter-in-place. If this expands to other areas or becomes mandatory, the garden will close. Check our web page for the latest information.

Now blooming at the Haven:

Ceanothus, many species. For more detail on this genus, see this previous post. 

Western redbud, Cercis occidentalis. This plant provides bright pink flowers early in the year, while leafcutter bees use its foliage for nest construction throughout the summer. This California native needs full sun and little to no summer water. It grows slowly, so it's worth buying a larger size for your own garden. It may be fed on by the redhumped caterpillar; damage occurs towards the end of the season so control is not needed.

Redbud leaves used in a leaf cutter bee nest

Redhumped caterpillars on redbud

Brandegee's sage, Salvia brandegii. This is a long-blooming California native sage. As you can see from the photo, which shows one plant, it can get quite large. Flowering from late January through May, pair it with the summer blooming native Cleveland sage (Salvia clevelandii) for season-long bloom. It also needs full sun and low summer water.

Bladderpod, Isomeris arborea. This is another long-blooming California native. It is at its peak in the spring, but will produce some flowers year-round. Our single plant is about 6 feet by 6 feet. Needs full sun and little to no summer water. 

Firecracker penstemon, Penstemon eatonii. This bright red California native is used more by hummingbirds than bees, and adds a jolt of color to the early spring garden. It's soon to be followed by the foothill penstemon, a bee favorite. The firecracker penstemon can take part shade and will re-bloom if given some water after the first flush of flowers. Like most of our native penstemons, it will go dormant in the heat of the summer, at which point watering should stop.

Bees to look for this week include honey bees and the blacktailed bumble bee, Bombus melanopygus. The latter seems to like the Brandegee's sage, so look for it there.

Blacktailed bumble bee, Bombus melanopygus, male on Brandegee's sage