Winter Is a Great Time to Tidy Up Perennial Stems for Pollinator Habitat

— Written by Elsa Youngsteadt — Contributors: Hannah Levenson | February 25, 2025 (Updated: Feb. 26, 2025, 4:06 a.m.)

Gardening for pollinators isn’t just about flowers—it’s also about stems. Many native bees nest inside hollow or pithy dead stems, and their nests can be destroyed during garden cleanup. To find out how to keep the pollinators safe--and your garden tidy--read on, or check out our new fact sheet and video!

So when can you tidy up dead stems in your garden without destroying bees? Much of the advice we found on the internet suggested waiting until late in the spring, but as bee biologists, we didn’t think that made sense. We thought spring would be when bees are moving into hollow stems, not out! But we couldn’t find any research that addressed this question directly - so we did the study, together with Extension agents and Extension Master Gardener℠ volunteers who sampled stems from 20 gardens in 10 counties in North Carolina across two years.

A photograph of a stem being split to reveal small bees inside — A stem being split open to find the small carpenter bees (genus Ceratina) residing inside.

After splitting nearly 3,000 stems, we found that stems are not occupied in their first winter. So, right after a stem finishes flowering is a great time to trim it back (you can leave the dead flower head in place so birds can get the seeds, but don’t wait until spring to trim it back.) Because, as we suspected, in the spring, bees are moving into last year’s dead stems and starting new nests.

What does this mean for you as a gardener? The great news is that by trimming stems - rather than cutting them all the way to the ground - you can create habitat for stem-nesting bees. Once you trim a stem, you should leave it alone and bees will use it until it disintegrates.

A three-panel photo showing a coneflower plant in bloom, then the same plant in the fall when the flowers have died, and finally, the same plant in the winter after the dead flower stems have been trimmed. — A plant undergoing the recommended stem trimming cycle, as seen in summer (A), winter before trimming (B), and winter after trimming (C). Solid ovals indicate the current year’s stems, which do not yet contain bees. Dashed ovals indicate the previous year’s stems, which could contain bees and are left undisturbed.

Bottom line: Trim stems in their first winter (after first frost but before last frost), then leave them alone. With this practice you’ll have both a tidy garden and a pollinator habitat.

For more details on what we found, the kinds of bees who live in stems, and their seasonal timeline, we made these two resources:

Fact sheet

(YouTube)