I will soon publish the results of the Bee Plant Survey that you answered back in November. Miriam Valere, a new beekeeper in Salt Lake City has been doing all the work, and I owe her a huge public thank you. For each plant Miriam has verified the scientific name, added the USDA hardiness zones where the plant grows, and linked to photos and more information.
Plant people of all sorts—gardeners, farmers, even beekeepers—rely on the USDA hardiness zones to decide whether a given plant can thrive in their area. But I think that perhaps too much weight is given to that one metric, especially when you consider what it measures and what it doesn’t.
In a nutshell, the USDA hardiness zones are calculated by averaging the minimum winter temperatures over a series of years. While that is an important number to know, it doesn’t take into consideration many other factors that affect plant life.
For example, I live on the 47th parallel in hardiness zone 7b. If you followed the 47th parallel across the continent you would go through Idaho, Montana, North Dakota, Minnesota and then Ontario, Quebec, Newfoundland and Labrador. None of these other places are in a zone 7b.
Likewise, if you look at other zone 7b areas, you will find them in places like the Carolinas, Georgia, Alabama, and Arkansas. Let’s take Abilene, Texas. It has the same USDA hardiness zone as I do, but Abilene gets 25 inches of rain per year to my 50. Abilene gets 243 sunny days per year to my 136. The average high July temperature in Abilene is 95, whereas mine is 77. At the winter solstice Abilene has about 10 hours of sun to my 8.5 (assuming you could see it).
All of these factors greatly affect the plants that will thrive in an area, and others I didn’t mention, such as relative humidity, are equally important. When you are selecting plants for your bees, remember to consider these other factors as well. For example, although some southern plants may survive much further north, they may not be able to blossom in places with limited daylight hours.
Other countries have adopted the USDA hardiness zone system. Canada uses it along with another, more in-depth measurement called The Agriculture Canada Plant Hardiness Zone Map, which also considers summer maximum temperatures and the length of the frost-free period. If you are in Canada, look at both of these systems.
In the Bee Plant Survey, we have divided the bee plants by state, province, and sometimes by geographic region so you can see which plants have proven useful to beekeepers in your area. I’m hoping the information will help you find plants that will keep your bees thriving and well fed in the years to come.