Spring garden cleanup & stem-nesting bees: When to cut perennial stems

Over the last several years, there’s been a big push to plant for pollinators. Homeowners are creating habitat in their landscapes – but many are unsure when (or how much) to clean up in spring.

When you cut back perennials can make the difference between supporting stem-nesting bees and accidentally removing potential nesting sites. Should you leave stems standing? Cut everything to the ground? And if you do cut, when is it safest?

Many resources suggest waiting until late spring. Researchers with NC State Extension noticed that recommendation didn’t have much hard evidence behind it, so they investigated by sampling roughly 3,000 stems from pollinator plantings across multiple gardens and seasons.

Their key finding: intact “first-winter” stems – stems that grew during the season and enter winter uncut and unopened – are generally not used by stem-nesting bees during that first winter.

The reason is simple: bees typically need an opening into a hollow or pithy stem, and intact stems don’t provide easy access.

Where it gets interesting is what happens next. Stems that remain standing and weather through winter often become better nesting sites the following growing season, especially once natural wear, breakage or deadheading creates entry points. In other words, leaving stems standing isn’t just “doing nothing.” It can set the stage for future nesting.

Practical Guidance For a Bee-Friendly Cleanup

If stems were cut, snapped or deadheaded during the growing season, treat them as potentially occupied. Those openings may already be inviting to bees, so it’s best to leave those stems standing and avoid cutting them again during winter or early spring.

For intact first-winter stems, the ideal trimming window is winter (after the first hard frost and before the last spring frost). At that point, you can:

• Cut to the ground if you want a cleaner look
• Or trim to 12 – 24 inches to keep things tidy and create ready-made nesting sites

Each year, focus your cutting on the previous season’s intact growth and leave older, already-weathered stems in place when possible. Those are more likely to contain nests.

You can’t always tell if a stem has been used, but the cut end can offer clues. An intact pithy center often suggests it hasn’t been occupied, while a small hole (sometimes with a bit of pollen dust) can signal possible nesting. When in doubt, leave it.

Finally, for anyone worried about getting stung: most stem-nesting bees are solitary and generally not aggressive – they’re unlikely to sting unless handled roughly.

When it comes to spring cleanup, it helps to think like a bee. A little restraint – and a strategic trim – can keep your garden looking cared for while also making it a better place for pollinators to live and reproduce.