How to help mason bees in your yard

Why mason bees?

We love mason bees. These small, solitary bees are amazing pollinators. Each mason bee visits around 1,800 to 2,000 flowers a day, and they pollinate 95-99% of them. In comparison, a honeybee may visit 700 flowers a day and pollinate about 5% of them. They are called mason bees because they use clayey mud to build protective walls for their cocoons.

Mason bees do not form hives and do not have aggressive behaviors. Males have no stingers, said Swansons Nursery, and the females rarely sting. “The few who have experienced the sting compare it to a mosquito bite. It does not cause anaphylactic shock.”

Mason bees are most active in early spring. This makes them great pollinators for fruit trees, which flower in spring.

Bee houses

In the past we have recommended buying bees from Crown Bees or renting them from Rent Mason Bees. From both firms you can get tubes containing mason bee larvae, nesting tubes or blocks, and a small bee house to hang on a sunny outdoor wall.

While using bee houses is a great way to help mason bees, there is increasing concern that raising solitary bees in close quarters creates problems. “Not only do dense bee settlements attract disease, mold and fungus, but those woodpeckers, parasitic wasps and mites also admire them,” said Honey Bee Suite.

Many species of birds and rodents will prey upon mason bees, Crown Bees said. They provide tips for how to use wire mesh or other materials to protect the bee houses.

Problems with parasitic wasps, mites and diseases generally occur when the nesting tubes or blocks are not cared for properly. Both Rent Mason Bees and Crown Bees are taking steps to counteract these problems. Rent Mason Bees does meticulous cleaning when bees are returned to them in the fall. Crown Bees individually inspects and cleans each cocoon.

Another option: grow plants with hollow stems

Another way to help mason bees is to grow plants with hollow stems. Several characteristics make upright hollow stems great bee housing, according to Honey Bee Suite.

• The stems are spread further apart, making it more difficult for diseases to spread and for predators, such as birds and wasps, to find the bees. Because they are spread out, it is also more time-consuming for predators to eat them.
• The stems naturally fall over and start to decompose after a couple of years. Adults will move on to other homes. This keeps pathogen levels low.

Year One

Choose and plant the right plants. Honey Bee Suite’s list includes lovage, elderberry, blackberry, teasel, drumstick allium, mountain mint, goldenrod, sunflowers, joe-pye weed and swamp milkweed.

At the end of the first growing season, use a sharp tool to cut the stems back to about 12 to 18 inches high, leaving them in the ground. You want a clean cut for smooth and straight openings. Another option, according to University of Minnesota Extension, is to cut stems to about eight inches and tuck them in the crotch of a tree.

Year Two

In spring, bees that are active will nest in the stems you left standing. “They will lay eggs in the stem and provision each egg with a nutritious ball of pollen and nectar,” said Tufts Pollinator Initiative. Bees will develop from eggs into larvae and adults that hibernate through winter.

Leave these stems standing all year. You can also start more plants for the next season.

At the end of the growing season, cut back the new, green stems produced this year for next year’s bees to use.

In the late fall or early winter, some stems may bend over or fall to the ground. Since we have wet winters, you may want to cut the stems at ground level and store them in a cool, dry place. Put them out in spring, but use an emergence box so the bees won’t reuse the stems.

An emergence box is an empty box with a lid and a small hole where bees can fly out. Bees prefer to lay their eggs in sunny locations. Most will not want to go into the dark box to find their old nesting tube but will use a new hollow stem. Honeybee Suite has more information about emergence boxes.

Year Three

In spring the bees will emerge from the hollow stems you planted the first year, and many will nest in the stems you planted the second year. “Now you’re on a roll,” said Honey Bee Suite. “You just have to keep going and you should have plenty of healthy bees to pollinate your orchard and garden crops.”

More ways to help mason bees and other native pollinators 

Reduce or eliminate your use of pesticides

This includes insecticides, fungicides, and herbicides. An insecticide called imidacloprid is especially insidious. According to Science, the pesticides “disrupt learning and memory in honey bees and several studies have shown solitary bees suffer the same kind of damage.”

Research done on blue orchard mason bees found that “bees that had consumed [imidacloprid] pesticides had 30% fewer offspring, compared with bees that had grown up without pesticides,” according to Science. Over two generations, the damage added up. Bees that were exposed to pesticides as larvae and then as adults would have about 75% fewer offspring than those that had not been exposed.

Add native plants to your yard 

Mason bees and other pollinators need food, primarily nectar. Choose a variety of plants that bloom at different times of year so pollinators have food throughout the growing season.

Here are 10 Pacific Northwest native plants for pollinators from Swansons Nursery.

• California hazelnut (Corylus cornuta var. californica)
• Vine maple (Acer circinatum)
• Bigleaf maple (Acer macrophyllum)
• Trillium (Trillium sp.)
• Redwood violet (Viola sempervirens)
• Salal (Gaultheria shallon)
• Alpine strawberry (Fragaria vesca)
• Trailing blackberry (Rubus ursinus)
• Oregon grape (Mahonia aquifolium)
• Western buttercup (Ranunculus occidentalis)

And here are links to a few other plant lists.

• Native Plants For Pollinators and Beneficial Insects: Maritime Northwest Region, Xerces Society (pdf)
• Pollinator Plants for Northwest Washington, WSU Extension (pdf)
• 12 plants to entice pollinators to your garden, OSU Extension Service
• Plants for Pollinators: A Regional Guide for Farmers, Land Managers, and Gardeners in the Pacific Lowland Mixed Forest Province, Pollinator Partnership and NAPPC (pdf)

Allow some clean water and wild spaces in your garden

Mason bees need a puddle of bare, muddy soil to pack into the openings of their nests. To help pollinators obtain shelter and food, choose some places to keep the grass longer and allow a few weeds along with branches or twigs.

We can help

We offer services to help you create and maintain a landscape that is friendly to mason bees and other pollinators. For example, we can design and install a landscape featuring native plants that provide food and shelter. Our natural lawn, tree and shrub care program will improve plant health, reducing or eliminating the need for pesticides. Contact us to learn more.