Bee Prepared: Overwintering Solitary Bees Made Simple

In this episode of The Evergreen Thumb, expert guest Bri Price joins us to explain how to prepare solitary bees for winter. From storing mason and leafcutter bee cocoons safely to managing moisture, pests, and disease, Bri covers essential tips to ensure your garden’s tiny pollinators survive the cold months. Whether you’re using a bee house or promoting natural habitats, this episode will help you support these vital insects and set them up for a successful spring. Tune in to learn everything you need to know about winterizing your solitary bees!

• WSU Honey Bees + Pollinators Program
• Instagram (@wsubeeprogram)
• WSU Bee Program Youtube Channel
• Protecting Our Pollinators – How to Support Our Solitary Bees – Episode 016

[00:00:00] Erin Hoover: Welcome to The Evergreen Thumb, your go-to podcast for up-to-date research-based horticulture and environmental stewardship knowledge to help you grow and manage your garden. Produced by Washington State University Extension Master Gardener Volunteers and brought to you by the Master Gardener Foundation of Washington State.

[00:00:16] I’m your host, Erin Hoover, a WSU Extension Master Gardener since 2015 and a certified permaculture designer and modern homesteader. WSU Master Gardener volunteers are university-trained community educators who have been cultivating plants, people, and communities since 1973. Are you ready to grow? Let’s dig into today’s episode.

[00:00:35] Welcome to The Evergreen Thumb episode 33.

About Our Guest

My guest today is Bri Price. Bri attended Oregon State University for both her undergraduate and graduate degrees in entomology and has strong interests in pollinators and education. She has been the WSU Bee Program Extension Coordinator for a little over a year and works out of the Puyallup Research and Extension Center.

[00:01:07] She does extension and outreach about honeybees and other bee pollinators through teaching seminars, facilitating workshops, blogging on the bee program website, writing educational fact sheets, and more.

She’s here today to talk to us about caring for solitary bees, uh, over the winter.

Before I jump into my talk with Bri, let’s cover the November gardening calendar.

November Gardening Calendar

[00:01:31] For planning, you want to assess outdoor spaces for areas lacking trees or shrubs and research appropriate choices for that chosen spot. You can also begin to force spring bulbs for indoor blooms in December.

In maintenance, it’s a good time to start cleaning things up and putting them away for the winter. Service your lawnmower, clean your tools, and put them away for the winter.

[00:01:52] You want to check your vegetables that are in storage and make sure to remove any that are going bad. You can place a cold frame over rows of winter vegetables to keep them going a little bit longer into the winter.

Place mulch around berries for winter protection. Cover rhubarb and asparagus beds with manure and straw.

[00:02:16] Make sure you drain any sprinkler systems that you have to protect those from breaking when they freeze.

Leave ornamental grasses up in the winter to provide texture in the landscape and to provide habitat for overwintering pollinators. Wait until late spring to cut them back.

[00:02:42] Watch for wet soil and drainage problems once the heavy rains start coming back and consider rain gardens or bioswales as long-term solutions to those. There are lots of ways to correct the drainage issues, but you want to wait until spring to actually do the work. So take pictures of the area or something like that so you don’t forget what the area looks like when it’s not draining.

[00:03:07] Let’s see, it’s also possible to take cuttings of rhododendrons and camellias for propagation in at least western Washington. Prune your roses back.

If there’s no snow cover and the ground is warm enough, be sure to water your newly planted perennials, trees, and shrubs every six to eight weeks, and give them a deep soaking, uh, to keep them from drying out.

[00:03:31] Sometimes we forget that, uh, ornamentals do still require water, especially if we’re having dry spells in the winter.

In planting and propagation, consider growing some herbs or greens indoors. chives, lettuce, cilantro, and things like that all are good options to grow indoors in the winter.

As long as the ground is not frozen, you still have time to plant spring flowering bulbs like tulips, daffodils, hyacinths, and crocuses, but don’t wait too long.

[00:04:02] Uh, let’s see. In pest monitoring and management, you want to rake and destroy any leaves or fruit that have fallen from trees that were diseased this year. This will help break that pest cycle, um, and reduce pest populations in your fruit in the coming years.

Check your firewood for insect infestations, and burn the affected wood first and don’t store it inside.

[00:04:26] For peaches, you want to treat your peaches four weeks after leaf fall for leaf peach curl and for shot hole diseases.

In western Washington, check for moss appearing on your lawn. It may mean there is too much shade or poor drainage, so you need to make corrections to those conditions if the moss is bothersome.

[00:04:49] So this could look like, you know, opening up plantings or maybe converting it to an ornamental bed, um, to let more light in. You know, it’s western Washington. Sometimes moss is just going to be there. I live on a prairie. It’s very fast-draining soil. There are no large trees to cast shade, and I still have moss. So, sometimes you just learn to live with it.

[00:05:15] During rainy periods in western Washington, you can use bait in the garden for slugs. Use traps or phosphate baits if you have pets because those are considered pet-safe. Continue to monitor landscape plants for problems but be sure not to treat unless you identify a specific problem.

For houseplants and indoor gardening, it is time to repot your amaryllis from last year if you kept it over the summer.

[00:05:42] Water and keep it in a warm bright area and fertilize it lightly when it begins to show new growth. And it’s time to reduce fertilizer applications for indoor houseplants if you’ve been fertilizing. So that covers the November gardening calendar.

Guest Introduction

[00:06:00] Now let’s move on to our episode. Well, Bri, thanks for joining me today. Welcome to the show.

Bri Price: Thank you so much for having me.

Erin Hoover: To start off, why don’t you tell me a little bit about yourself and your work with WSU?  

[00:06:11] Bri Price: Um, I’m the extension and outreach coordinator for the WSU Bee Program. So, I do a lot of outreach, mainly with hobbyist beekeepers, but I’ve been getting more into working with gardening groups and educating about native bees as well.

How Overwintering Differs Between Different Solitary Bee Species

[00:06:29] Erin Hoover: Great. So today we’re talking mostly about the care of solitary bees in the winter. So, can you tell us a little bit about how overwintering differs between species such as mason bees or leafcutter bees and other solitary native bees?

[00:06:45] Bri Price: Yeah. The major difference in overwintering with mason bees and leaf cutter bees is the life stage that they hibernate in throughout the winter.

[00:06:55] So mason bees overwinter as adults inside their cocoons. As the weather warms in the spring, they emerge, mate, pollinate, and begin nesting again. But for leafcutter bees, they overwinter as a dormant, uh, pre-pupil stage inside their leaf-lined cells. So, they don’t have, um, the, you know, the same cocoons like mason bees do.

[00:07:18] They line their nests with leaf pieces and as temperatures warm more in the summer, they’ll complete their transition to adults and then emerge.

As for other native solitary bees, there are so many different species in Washington State. So something that a lot of people might not know is many solitary bees are actually ground-nesting bees instead of nesting in cavities like mason bees and leafcutter bees.

[00:07:44] So ground-nesting bees can overwinter in various stages, um, like larvae, pupa, or adults, depending on the species.

How to Support Overwintering Solitary Bees in the Garden

[00:07:53] Erin Hoover: How can gardeners best support overwintering solitary bees in the garden?

[00:07:59] Bri Price: Um, so since many solitary bees are ground nesting, um, really the, the best way is to leave areas of undisturbed soil, but yeah, some do nest in cavities.

[00:08:10] So, um, I usually recommend in your garden spaces, leaving leaf litter behind plants that dry out and leave hollow stems are really beneficial for cavity-nesting bees, dead wood, brush piles, things like that, essentially like a messy garden space is going to provide natural shelter and nesting sites for overwintering bees.

Preparing Solitary Bee Nest Blocks for Winter

[00:08:33] Erin Hoover: Okay. So now for like the houses, if we’re supporting mason bees or leafcutter bees, how do we prepare them for winter?

[00:08:43] Bri Price: Um, in the late fall, uh, like October or November time, that’s a good time to open up the nest blocks. Um, so let me just go back for, the end of summer, you would want to take those blocks down to limit predation throughout the summer.

[00:09:00] Then in the fall, especially with mason bees, when they’ve spun, they’ve finished spinning their cocoons, that would be a good time to open up those nest blocks and remove them and clean them.

Usually when I talk with people about removing or cleaning these nest blocks, if someone doesn’t want to open the nest blocks, um, and actually clean everything, they can at least, just take them down and store them in like a cool shed or garage is better than leaving them out in the, you know, subject to the, um, the weather and birds and other predators, like all fall.

[00:09:36] Um, so, uh, mason bee cocoons in particular, they’re hydrophobic, so they can be, uh, like cleaned off with water and that wouldn’t, wouldn’t harm the bee inside.

So a lot of, uh, a lot of the time when you open up nest blocks, you’ll see some debris on the cocoons, like frass, like these dark little, um, brown pellets along the cocoons or lots of pollen mites that will just look like, like yellow sawdust almost on the cocoons.

[00:10:08] If there are a lot of pollen mites or debris, it is best to clean them. So, you can do a mild bleach wash and that is, um, the recipe for that is one tablespoon of like household Clorox bleach to eight cups of water, and you can put all the cocoons in there and just kind of gently, um, stir it around with a spoon or your hand.

[00:10:31] After just like one to two minutes, you can rinse those cocoons with water and then leave them to air dry on like a screen or a paper towel. Then that would be a good time, also to hold the cocoons up to light to see what’s, um, inside and you can sort of see through the cocoons where if they’re diseased or, um, they’re bees that just didn’t develop all the way or died because of parasitism.

You can discard those and that’s helping whatever cocoons you are saving for spring to be the more viable, healthy bees.

[00:11:06] And, um, just as a note, this is not what you do with leafcutter bees. You don’t want to, um, do that because the type of thing they’re overwintering in is like leaf cavities. They’re just with a ton of really meticulously picked leaves rolled around.

So they don’t have that hydrophobic protection. Um, so with leafcutter bees, you just can remove the leafcutter, uh, like little cavities, um, and put them in a container, but you don’t want to wash them.

Managing Different Types of Solitary Bee Nest Blocks

[00:11:38] Erin Hoover: I know there are a few different kinds of nesting blocks for bees. Some, some are you can take apart and some are more permanent. I guess this would be a good word for it. So how do you clean or manage those houses…for winter?

[00:11:56] Bri Price: Well, if people have the type of nest blocks that they can open or line with like paper nesting tubes or paper straws, those are really easy to open up and clean.

[00:12:07] But if people are using like the commercial, commercially sold, uh, houses with like bamboo that’s like super glued into the back where you can’t open up those straws or like wood with holes drilled in them. Those are harder to clean. And so, yeah, taking them down is really the best thing you can do.

[00:12:32] Um, and then in the spring, when they’re starting to emerge, to limit their ability to go back to that nesting material and put out the kind that you can open. That’s the best way to help them.

Ways to Store Solitary Bee Cocoons in the Winter

[00:12:41] Erin Hoover: So what is the best way to store solitary bee cocoons over the winter?

[00:12:46] Bri Price: Uh, mason bee cocoons can be stored in your fridge. Um, so you can leave them in the nest block as well, but if you’re going to harvest the cocoons, you can keep them in your fridge to keep them cold.

[00:12:58] This is beneficial. More beneficial than leaving them out because they’re less likely to experience like extreme temperature fluctuations or predation, but if you end up doing this, you want to keep the cocoons in a ventilated container with some moisture to keep them from drying out. So like a paper towel that’s just a little bit wet, not dripping wet, and putting that in a dish in your fridge.

[00:13:24] But then your wanting, you’re wanting to check that, um, you know, every week or so to make sure that no mold has developed or that the paper towel is still slightly wet because you don’t want the cocoons to be too dry.

Ways to Protect Solitary Bee Cocoons from Predation and Parasitism

[00:13:37] Erin Hoover: What is the best way to prevent predation or parasitism in the cavities of the houses or blocks?

[00:13:48] Bri Price: Well, um, for, for mason bees, they’re really only adults, um, until about, you know, late spring, early summer, and then they’re developing inside their nests for the rest of the year.

So, a good way to protect them from predation is removing the nest blocks, or if you can’t physically remove them, like say they’re affixed to some type of infrastructure in your yard, you can put like tulle or something like, uh, tight mesh around it, where birds can’t get in or other like parasitic wasps that are like really microscopic.

[00:14:18] That helps limit their access to getting in, especially like we have some parasitic wasps that are known to get in in the summertime where they’ll, find their way into the nesting area and pierce through the cocoons and lay their eggs, and then the parasitic wasp offspring emerge. So that’ll kill your bees.

[00:14:43] So limiting that access to those predators will really help your bees in the following generation.

Mold and Disease Concerns for Solitary Bee Cocoon Storage

[00:14:52] Erin Hoover: What about mold or disease in the cocoons while they’re in storage?

[00:14:59] Bri Price: Yeah, if, um, if the cocoons develop any kind of mold, um, you could just rewash them like you would when you’re first harvesting them from the nest box.

[00:15:08] So just that really mild bleach water, um, and then air drying them before returning them to the container.

How to Determine When to Place Nest Blocks Outside in Spring

[00:15:16] Erin Hoover: When is it time to put the cocoons or the blocks back out in the spring? How do you know it’s time?

[00:15:27] Bri Price: Um, it’s very temperature-dependent. So for mason bees, nest blocks, I mean, they can be put out in early spring when the temperatures are starting to reach like 50 to 55 degrees Fahrenheit pretty consistently.

[00:15:40] Usually that’s, you know, late February. Um, mid-March for areas in western Washington where I’m at, and some bee hotels have a little area that you can put cocoons in. So, if you, you saved your cocoons over winter and you have them ready for emergence, you can put those cocoons in that little area. Then as those temperatures start to warm, they’ll start emerging, um, mating and then, you know, going back into that nest block to, you know, lay more eggs and establish the next generation.

[00:16:13] For leafcutter bees, it’s a lot warmer. So once temperatures are around like 70 degrees Fahrenheit more consistently, they’ll begin that metamorphosis to finish their development from that dormant pre-pupil stage to the adults, and then they’ll start, you know, emerging and, um, doing their thing.

[00:16:35] But yes, uh, mason bees are more spring bees and leafcutter bees are more summer bees.

Why do Solitary Bee Nest Blocks Need to be Managed?

[00:16:42] Erin Hoover: I guess we kind of touched on this, but why do, like, mason bee hotels or, um, other bee blocks need to be managed?

[00:16:51] Bri Price: A lot of people that hang these bee hotels might have good intentions to, like, provide habitat for bees, but hanging them and then doing nothing with them can do more harm than good because of what predators and parasites can get in.

[00:17:05] Most solitary bees don’t naturally nest in such large groups like a bee hotel that has 20-plus cavities for the bees to nest in. So, if you think about it, they’re kind of more vulnerable in bee hotels because these predators see this huge area where there are tons of hosts available.

And so, um, poor management can be like leaving the nest blocks out all year long, not cleaning them in the fall where you’re removing those diseased or parasitized, um, cocoons and, you know, encouraging their offspring to come out in the spring.

Determining if a Cocoon has been Parasitized or is not Fully Developed

[00:17:46] Erin Hoover: Okay, back to what you were saying when you were inspecting the cocoons. It sounded like the pollen mites were fairly obvious to tell, but how can you tell if a bee has been parasitized or if it is not fully developed in the cocoon?

[00:18:02] Bri Price: Holding that, holding the cocoons up to light, you can really see, like, if there’s a lot of, like, um, empty space in the cocoon, something’s not right.

[00:18:10] It’s either a dead bee or it might be, you know, something that just isn’t, you know, your bee. Um, normally the cocoon will be pretty full, and just as a note, female and male mason bees specifically, there are different sizes. Males are smaller, but the cocoons are also smaller. So they’ll be, you know, they’ll correlate to which sex they are.

[00:18:33] But yeah, holding up to the light. You can see if there’s any kind of like amber color coming through. There’s empty space. You could just discard that cocoon.

Final Thoughts on Solitary Bee Winter Care

[00:18:44] Erin Hoover: Is there anything that you would like to add about solitary bees and caring for them over the winter?

[00:18:50] Bri Price: Yeah, I think something about solitary bees, especially cavity-nesting bees, um, the size hole that they find will sort of directly correlate to what species will use that hole.

[00:19:02] So, a lot of these commercially sold bee hotels just happen to be the diameter, or maybe they’re designed to be the diameter for these blue orchard mason bees. So most often when a lot of people are keeping mason bees, that is the species that they’ll likely be supporting. Some other Osmia species, um, blue orchard mason bees are Osmia lignaria.

[00:19:25] Some other Osmia might use that space, but blue orchard mason bees tend to be on like the larger end of the size um, variation within Osmia, and leafcutter bees are actually a lot smaller.

So nest blocks for leafcutter bees can look just like mason bee nest blocks but with much smaller holes. So that’s just something kind of a fun fact for if people are looking to maybe support leafcutter bees more than mason bees or something.

[00:19:54] Erin Hoover: That’s good to know. Um, and so that’s kind of the same thing you said with the, the size of the, the bees to the cocoon is going to be, um, correlate to the size of the bee. So like the females are larger.

[00:20:08] Bri Price: Yeah, the female cocoons are just a little bit larger and the male cocoons are a little smaller. It’s not like a huge size difference. But, yeah, just something kind of fun to know.

[00:20:15] Something else too, when mason bees are laying eggs, they lay, um, so you think of like a linear cavity, like a straw, and they’re laying in the far back first, they lay female eggs first, and then tend to have the males, and the males actually emerge first, before the females do, and then they’ll, they’ll mate as soon as they can.

[00:20:37] And then the males don’t really serve a purpose after that. The females are the ones going and foraging and making the new, um, the new generation.

Reasons Why Bees Might Choose Not to Nest in an Available Nesting Block

[00:20:51] Erin Hoover: So a while back, I had a question from a listener about, she was concerned that bees were not nesting in her bee hotel and was wondering, wanted to make sure that or how she could get them to nest there or, you know, if there was a problem and my first thought was that they’re probably finding plenty of other places to nest.

[00:21:13] But do you have any thoughts on that?

[00:21:16] Bri Price: Yeah, I mean, I mean, that’s, that’s probably good insight as well as, you know, maybe the bee hotel they have out was just not the right, uh, length or diameter for the bees in her area. Um, I know I saw once, um, a little like hexagonal, uh, thing that you can hang at Target that had bamboo straws in them.

[00:21:39] And these, these were like massive diameter tubes. And I’m just thinking like, what would nest in that? So, you know, that could be, um, a possibility.

Specifically, mason bees, need some type of mud source nearby to be able to make their mud-lined cavities within the nest block. So, if they’re just, you know, if they’re in a yard where they’re not getting these other resources they need, that would make nesting there kind of harder for them.

[00:22:08] So something else to, to think of any final thoughts. I just thought maybe I could plug my YouTube video. So I’ll put that in here. Okay. Um, the WSU Bee Program just created a how-to video highlighting the ways people can manage blue orchard mason bees all year long, and it’s on our WSU Bee Program YouTube channel.

[00:22:35] We collaborated with Rent Mason Bees, which is a large solitary bee distributor, and they also have a ton of information on how to thoroughly clean nest blocks.

So for, especially for this winter management or going into fall, they have some good resources on how to clean the cocoons and the nest blocks.

[00:22:54] Erin Hoover: All right. We will link to that video in the show notes for the life cycle or caring for them throughout the year, and also, um, to some of the resources from Rent Mason Bees as well.

Listeners can check out the show notes and get more information. All right. Well, um, Bri, thanks for joining me today.

[00:23:13] This was, uh, very informative.

Bri Price: Thank you so much for having me. I had a lot of fun.

Erin Hoover: Thank you for joining us on this episode of The Evergreen Thumb, brought to you by the WSU Extension Master Gardener Program volunteers and sponsored by the Master Gardener Foundation of Washington State. We hope that today’s discussion has inspired and equipped you with valuable insights to nurture your garden.

[00:23:38] The Master Gardener Foundation of Washington State is a nonprofit organization whose primary purpose is to provide unifying support and advocacy for WSU Extension Master Gardener programs throughout Washington State. To support the Master Gardener Foundation of Washington State, visit www.mastergardenerfoundation.org/donate.

[00:23:57] Whether you’re an experienced Master Gardener or just starting out, the WSU Extension Master Gardener program is here to support you every step of the way. WSU Extension Master Gardeners empower and sustain diverse communities with relevant, unbiased, research-based horticulture education.

[00:24:16] Reach out to your local WSU Extension office to connect with master gardeners and tap into a wealth of resources that can help you achieve gardening success. To learn more about the program or how to become a Master Gardener, visit www.mastergardener.wsu.edu/get-involved.

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