How To Pollinate Your Greenhouse with Honey Bees

Encourage pollination of your greenhouse crops by giving your bees a direct-access pass to the world of indoor growing.

by Dawn Combs
PHOTO: Dawn Combs

On our farm, Mockingbird Meadows, in central Ohio, we’ve been living and working alongside our bees for almost 10 years. They’re an amazing asset to both our vegetable and herb production. One of the places we’ve most enjoyed watching them is our greenhouse. We began to wonder how we could facilitate their work on a more purposeful scale.

Greenhouse pollination around the world is typically done by bumblebees (Bombus spp.), fascinating creatures that do their jobs well, especially in enclosed spaces. There are arguments in favor of choosing the bumblebee over the Honey bee (Apis mellifera) for this type of work: They’re active at lower temperatures than the Honey bee, are more efficient pollinators, work later in the evening and earlier in the morning, are native to the United States, and are less likely to sting you and your workers. When I first began researching greenhouse-pollination solutions, I was almost swayed by the bumblebee’s merits—and coming from a Honey bee keeper that says a lot.

I was ready to jump on the bumblebee bandwagon until I read the fine print: The bumblebees’ life cycle does not lend itself to a sustainable greenhouse pollination scheme. They live only four to 12 weeks, meaning you constantly need to purchase new colonies. Contrast that to a Honey bee queen that lives more than 2 years and continues to lay eggs, replacing workers as they die and raising a new queen if needed, and that puts me firmly back in the Honey bee camp.

Two Pollination Solutions

greenhouse is a challenging space to encourage natural pollination. On our farm, we have 35 stand-alone Honey bee hives. Our small greenhouse is 12 by 24 feet, and we allow pollination to take place during the summer by opening the top vents and front doors of the greenhouse during the day. If your needs are limited to your typical growing season, using Honey bees for pollination can be this simple. Just locate a hive next to the greenhouse and be sure it is accessible to them from early morning until after the sun has set in the evening. This length of time allows the last stragglers to return home without getting trapped.

However, if you’re attempting to grow in a large greenhouse space or are trying to extend your growing season, simply having a hive somewhere on your land will not cover your needs. At this point, you might want to place a hive directly in the greenhouse. This sounds simple, but actually requires quite a bit of planning. In the height of summer, a flourishing colony can contain upwards of 60,000 bees—that’s quite a lot of bees to negotiate when you want to work in your greenhouse.

Bring the Bees Inside

Regardless of the size of your greenhouse, it’s not advisable to keep bees shut inside at all times. While tomatoes are nutritious, if you ate nothing but tomatoes every day, you would get sick. Bees also need a variety of food (aka pollen) sources to maintain a healthy diet. Setting up your greenhouse to provide access to both its interior and the great outdoors will help your hive thrive.

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Locate your hive on the inside wall facing southeast so as to take advantage of the earliest warmth available each day as the sun rises. This location will get your bees working as early a possible for maximum production. Remove a greenhouse panel, situate the hive in the opening and seal around the hive to keep your greenhouse weathertight. If your greenhouse isn’t paneled, you can also reduce the hive entrance to a PVC tube that provides an exit from the hive to the world outside your structure.

Granting bees access to the greenhouse will also be influenced by the hive structure. Regardless of which structure choice you use, you’ll need to drill a small exit hole for the bees. Place a removable cover over this hole; originally, we liked wire mesh, but the bees insist on filling this up with propolis to keep out the light, so we ended up repurposing a wine-bottle cork. The corked hole gives your colony ample access to the outside, but when you remove the covering inside your greenhouse, they’re also free to pollinate your indoor crops.

Ventilation is important for both your plants and for a greenhouse hive, so locate your colony in an area where fans provide plenty of circulation. We have found it necessary to place wire mesh over the back housing of greenhouse fans when pollinating with Honey bees. Without a barrier, members of your pollination workforce can be pulled into the fan and killed.

Winter To-Do List

Your greenhouse hive will require extra attention throughout the year. In winter, our standalone hives are exposed to temperatures that signal the bees to form their winter cluster. They refrain from leaving the hive until the air temperature is between 60 to 65 degrees F. An unheated greenhouse hive might have temperature fluctuations that encourage flying during the day and clustering at night. If your greenhouse is heated, the bees will definitely want to fly most days. It isn’t necessary to block their entrance to the outside world during cold days—they will only fly out when it’s warm enough. Whether or not you heat your greenhouse, you’ll likely need to have ample honey stores in reserve to feed them when they cannot supplement their diets outside.

It’s probably a good idea to have a plan in place for “thinning the herd,” so to speak, especially if you have a heated greenhouse, because the bees will continue to grow their colony. You could use this greenhouse hive to move frames of workers and brood into weaker outdoor hives during the warmer months, increase your operation or help other beekeepers get started with native-bred nucs. However you do it, you’ll want to keep this colony at a manageable size—watch for clusters hanging off the front porch or signs of swarming just as you would with an outdoor hive.

If you’re a beekeeper hoping to use bees in the greenhouse, be prepared to go through a bit of trial and error to strike a balance between your colony size and the size and purpose of your greenhouse.

Honey bees are definitely not the most popular choice for greenhouse pollination. There are a number of drawbacks, including less efficient pollination and potential overcrowding. However, they’re worth a second look, particularly if you already have bee colonies on your farm or are interested in a sustainable solution.

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