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When should I put my mason bees outside?

Good question. If you are keeping mason bees in cold storage—whether in a garage, shed, or refrigerator—it is time to get them outside. Although conditions differ with latitude, nature tells us when the time is right.

As a rule of thumb, when things begin to bloom, the mason bees should be free to emerge. The blooming plants you see should be within a couple hundred feet of the mason bee housing. Unlike honey bees, mason bees will not fly long distances to find food, so it has to be close.

Early blooming plants here include crocus, scilla, vinca, skunk cabbage, and snow drops followed quickly by forsythia, dandelion, and oemleria. Once you see a few things start to bloom, you can safely put your bees outside.

If you don’t trust yourself to remember by looking at plants, just think March 1. Spring mason bees (Osmia lignaria) are generally active March, April, and May, so March 1 is a reliable date to use.

Although some people will keep mason bees in cold storage through April, I think it is better for the bees to be active when their wild counterparts are active. This will give your bees the best opportunity to mate with local wild populations and maintain maximum genetic diversity.

You can minimize the danger of wind and cold with a few simple steps:

  • Mount your mason bee house so it faces south or southeast. This will provide maximum sun exposure.
  • Attach a sloping and overhanging roof to your bee house to shed excess rain, or mount the bee house under an eave.
  • Plant early blooming flowers close to the mason bee housing. The males will emerge first and need nectar-producing flowers right away. The females will emerge later, and they will require both nectar- and pollen-producing blooms.

I saw my first mason bee last week on March 13. He was drinking nectar from a Vinca minor while all around him honey bee workers and queen bumbles were working the Scilla.

A healthy male mason bee sipping nectar from Vinca minor. Photo © Rusty Burlew


HB (@Hello_Kitty_)

Ooh, you’re making me feel like I’m behind on my duties! I always wait for the Spring Equinox, and even then I only put out a portion of my cocoons, maybe 25%. A week later, I put out another 25%. I put out the rest when I see mason bees have hatched and are using my nest.

Colorado winters have a bad habit of not wanting to end. Last year each time I put cocoons out, we had an unexpected snow storm. Each time, it was cold enough to destroy whatever was flowering… no maple blossoms, no crabapples, no ornamental pears… poor bees had nothing to eat. I finished the season with fewer cocoons than I started, and the cocoons I have are on the small side. 🙁

I worry that my bees are using up their fat reserves, but I am still waiting for the buds on my pear tree to swell just a little bit more.



If you’ve got a system that works, you shouldn’t feel bad. All beekeeping is local, even mason bee keeping.

Barbara Blackburn

Hi Rusty, Just new to your site but it looks so informative! Do you have a favorite type of house for your mason bees? If so, can you tell me your preference? One with removable straws or not?
Thank you,



If you want to raise just mason bees (rather than housing a variety of bee species) then I would use paper straws. Hairy-footed mites are definitely a problem when you have a monoculture of mason bees.

Glen Buschmann

HI Rusty –

Unless the beekeeper is running a commercial operation that must manipulate emergence, I encourage people to put stored mason bees out early and let nature set some of the schedule. Males emerge first, assess conditions, and if warranted helps females get out, (he cuts open the cocoon from the outside, pulls her out of her sleeping bag). Tunnel systems, (this includes straws) seem better than loose cocoons for this, as the cocoons are in order – males in front, females in back. Bees generally stagger their emergence based on conditions, waiting for breaks in the weather.

Of course Colorado is different than PNW, and bees are kept in the fridge as much to protect them from getting too cold as too warm. I wonder if there may be other native pollinators better suited to conditions described, (they maybe won’t live in human-made housing, but that is o.k. The challenge is that the natives may be unaccustomed to some of the early blooming Eurasian crop plants we grow that bloom on a schedule different than Colorado. I also might also look into outdoor storage that is better insulated against temperature fluctuations. As you point out Rusty, the closer to the local ecosystem the better.

Bees seem to vary their size quite a bit, depending on both food and housing available. I had a male mason bee emerge today bigger than the typical female, from one of my larger diameter tubes. But small works, might be better in some circumstances. Maybe Colorado mason bees will prosper better as small bees in 1/4″ tunnels.

My favorite system is botanical tubes — empty hollow plant stems. One reason I like botanical tubes is size variety. Botanicals also can go outside with less protection. Because every location is different I won’t name specific plants except to mention that some folk use bamboo which works but is tough to cut. Instead, I’d explore, cut different tall fast-growing plants and look for hollow stems. If suitable, then give the stems a try. Paper straws work fine, but paper is water absorbent, so they need more external protection. I make my own by rolling newspaper around a 5/16″ or 3/8″ dowel. YOU MUST LINE EACH NEWSPAPER TUNNEL WITH PLAIN PAPER, (no newpaper ink exposed inside the tunnels).

Glen B
Olympia, WA

Steve - Busy Bee Farm - Larkspur, Colorado

Hi Folks – new to this site – caught you via a Google Alert. re: this topic – I am confused. By the question I assume you are bringing your mason bees inside somewhere and then putting the back out again? From my experience, I question why this is/was done. Mason bees that build out into an artificial or natural space will emerge when they are programmed to – “need to” – if you will. I can see no reason to bring them in unless there is a fear of predation by some other insect or animal. In which case, I would still leave them outside and take measures like hardware cloth or a high location to take care of this worry.

Steven Lechner
Busy Bee Farm
Larkspur, Coloraodo


Hi Steven,

Welcome to the site. Yes, I agree. I do not bring my mason bees inside, but there are people who do. One of the reasons here in the Pacific Northwest is the rain. Here in the coastal areas we have rain from October thru June—basically nine months of it. I go out of my way to keep my mason bees sheltered, but if you don’t have shelter they will “sog out” by spring—mold, fungus, you name it.

The other reason people may have them indoors is because they mail-ordered them. They arrive in a loose tube, not a good overwintering site, so people keep them inside till spring. I wrote the post for those people who have mail-ordered them and are unsure when to put them out.

I agree that outside is where they should be so they can overwinter properly and decide for themselves when to emerge. Not everyone agrees with that philosophy, however, and so I’ve tried to give those folks some guidelines for choosing a time.


Steven, I live in Colorado just west of Denver. Do you think I can have success in raising mason bees? I have a lot of fruit trees, but they don’t bloom till around the middle of May. Thanks Ron


This is my second year with mason bees. As I understand it one major reason to bring them indoors for winter is to keep them away in the fall from parasites. I noticed some parasitism on some cocoons left outside past June 1st. I would rather keep them outside all year but had parasites the first year so I’ll continue bringing them in.


I refrigerate my cocoons because of the erratic temperatures. A few days above 50 in February, and the bees might start emerging and find no blooming plants to feed on.


Excellent reason.


They did not return ? Thank you


This is new territory for me overall. I am merely exploring the idea of a bee house, but have one big question. IF they collect and store their pollen and turn out to NOT be mason bees that seal the openings, will this be in conflict with the 3 hives of honeybees already on the property? Will this encourage robbing from them?



I don’t know if I understand your question. The only thing that will build in the tubes are solitary bees (there are many species besides masons that could build in the tubes, depending on the hole size) and a few types of solitary wasps. None of these insects pose any threat to a honey bee colony. Robbing of honey bee colonies is conducted mainly by other honey bees or by social wasps that also live in large colonies, such as yellowjackets and some hornets. Also some ants attack honey bee colonies, but again, ants are social and live in large colonies.

There is no colony behavior with solitary bees and solitary wasps, which is why they are called solitary. One female bee or wasp builds and maintains her own nest. They may live in communities, but each nest (tube) is maintained by one female bee. I can’t imagine anything living in a mason bee house being a threat to a honey bee colony.


Hi from Colorado Springs, CO. We were watching PBS and saw a show on Mason bees. Now we are interested in building our own house to put in our 8×10 ft garden. Being late March, we will put it out now. Glad to find a site where we can ask questions as we continue in this process. Thank you.


My mason bees started to emerge and there’s no flowering going on, some dandelions, none of my fruit trees yet, they’re about two weeks from bloom. It’s April 28th and were still getting snow. Will the bees that have hatched make it, and is there a way to put off the hatching in the future till the second week of May?



There’s nearly always something in bloom, and the bees are better at finding those things than we are. Mason bees are fine in cooler temperatures than many bees, and they know how to care for themselves. You can put off hatching by keeping them in the refrigerator, but you don’t want to go too late. The males hatch a week or so earlier than the females, and you don’t want your fruit trees to come into bloom with only the males around.


Thanks so much for getting back with me.


I recently bought a mason bee house if I hang it near my garden will the bees move into it? or do I have to buy bees? Should I wait until spring to set the house out or should I put it out now?



You can just put the house outside, and if you position it well, local mason and leafcutting bees will nest in it. It is my belief that it is better not to buy bees because locally adapted bees will do better, and you don’t run the risk of introducing a bee pathogen or parasite. The openings should fast south or southeast and be in the sun most of the day, particularly in the morning hours. I don’t know where you live, but I like to put them out in early spring before the first fruit trees bloom. If you put them out now, you run the risk of getting earwigs and other undesirables. I put mine under the eaves of my house and garden shed, which adds a little rain protection. It’s fun to watch the bees build. The mason bee species will seal up their holes with mud, and the leafcutting bees will use colorful petals or leaves. Too cool.

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