Inside: Mason bee cocoons need a few days of warmth before the bees emerge. In nature, the bees emerge when the first flowers bloom in spring. You can wait a while longer if you have a specific crop to pollinate, but waiting too long is risky.
If you are keeping mason bees in cold storage—whether in a garage, shed, or refrigerator—when is the best time to put them outside? Although conditions differ with latitude, nature tells us when the time is right.
As a rule of thumb, as soon as things begin to bloom, the mason bees should be free to emerge. The blooming plants you see should be within a couple of 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 snowdrops. Forsythia, dandelion, and Indian plum (Oemleria cerasiformis) come next. 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 in March, April, and May, so March 1 is a reliable date to use.
You can wait for certain crops
Some people like to regulate the timing of mason bee emergence so it coincides with a particular crop they want to pollinate. This works to some extent, but be careful. It can take a couple of weeks for the bees to emerge once you remove them from cold storage. If you wait too long to put bee cocoons outside, your bees may emerge too late.
Although some folks 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 maximize genetic diversity.
Keep your mason bees safe
You can minimize the danger of wind and cold with a few simple steps:
- 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.
- Place your cocoons in a hatching box (emergence box) to maximize their safety and discourage predators.
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.
Honey Bee Suite