Amsonia hubrichtii, center right, in the fall, not long before they started falling over.
When I recently wrote about which leaves it’s best NOT to leave on top of which plants, I also confessed to confusion over the question of leaving stems intact for stem-nesting bees. The consensus seems to be that whenever you cut them, it’s best for bees to cut them back to varying heights from about 8 to 24 inches, and leave them in place indefinitely – because it’s not until the stems’ SECOND YEAR that young bees emerge from hibernation there.
But if for some reason it doesn’t work for you or your garden to leave the shortened stems in place indefinitely or for at least 18 months according to several sources, is there an alternative that still could help the targeted bees? Or how about if your perennial stems aren’t standing up but are flopping over, and you’ve read several places that stems lying on the ground get too soggy (or something) to be useful to the bees, so it’s best to prop keep them vertical?
Well, most of the stunning stems of my three AmsoniaS shown above had fallen to the ground by early winter, so I gave myself permission to bundle and prop them up with the help of the rebar originally used for displaying deer-spooking CDs.
This next photo shows the resulting bundles (and a lone CD) in December. Removing the fallen stems uncovered the ground around the Amsonias in time for spring bulbs and some spiderwort to pop up around them.
But there’s one more purpose served by propping up the stems – screening! Notice to the left of the shed there’s an opening. That’s where pedestrians pass by on interior sidewalks (iconic to our “New Deal Utopia”) en route to the town center. And they had a clear view of me in my garden or on my porch – at least until the hydrangeas (strategically sited for screening) leaf out again.
The stems also help hide some chainlink fencing beyond.
Another view of the bundled stems. At least in this spot, I like the look!
Here’s a recent view of the stems behind the emerging leaves of oakleaf hydrangeas.
I tried the same technique with milkweed stems at my adopted garden, again with the help of rebar.
Still Questions
- How would I know if stem-nesting bees are using the stems that I’ve so carefully propped up for them?
- Further googling has uncovered a wider array of opinion on whether stems really need to be vertical, with some experts assuring us that stems are still helpful if they’re lying on the ground or gathered into a pile somewhere.
So my experiment will continue but sadly, the results may never be in – unless I divert my university studies to the Department of Entomology. (Unlikely in the extreme for my humanities-bent brain.)
I think your stems look good. Part of the landscape. I struggle with when to cut things back as old stems make it hard to see all the bulbs you planted, or walking on thawed and wet soil compacts it. I tend to snip everything up small to become mulch so with any hollow stems I just cut them shorter and then take the bigger top pieces and put them out near the compost pile. It can be hard to ‘garden’ when you have to consider the consequences of such.
So, I have had the same dilemma. I started leaving stems over the winter a few years ago for the bees. Then, like you, I read that it takes 2 years for them to finish the cycle. I have gardens for my visual pleasure in addition to supporting the insects and animals, and dead stalks in the beds interfere with that. What do you do when the new growth amsonia comes up? I left mine until that point, then cut the old stuff down.
I cut down all the stems in winter and stacked them as you see in this post, so there was no problem with seeing the new growth on the amsonia
Thanks for the clarification. I leave some stuff in areas that are more warm season beds, but in my spring beds where I want to enjoy the delicate beauty of emphemerals and overall design, I clean it up earlier. I rationalize that I move the debris to the wooded edges of our large property and hope the inhabitants manage OK with that plan.
I have many bees nesting in stems in my garden, so I think I can provide some clarity.
It is mostly small carpenter bees in the genus Ceratina that use these stems. They cannot get into an intact stem. It has to be cut to provide them an access point. In fact, very few insects can bore into an intact stem. It is a common misconception that all kinds of bugs are living in the stems you leave up all winter that haven’t been cut. Only a few insects are able to get into those stems, and those bugs are generally considered pests.
I cut my sturdiest perennials back to about 12 inches or so in late winter and leave them like that indefinitely. How do you know if the bees are using them? You’ll see a perfect round hole in the end of the stem where the mother chewed her way in. Also, you can watch them! They’re out in force in my garden right now, in Portland. They are tiny, like flying ants, black and shiny. Small carpenter bees are some of the first native bees to emerge and they’re active all season. Each female will make a nest, provision it with pollen, and lay eggs on the pollen. The babies will overwinter inside the stem and emerge the following year to repeat the cycle. The females may turn around and reuse that same stem. That’s why you want to just leave the stem and not cut it again. The stem may be occupied pretty much continuously, until it breaks down.
I’m not sure if the bees will use amsonia. It may be too floppy. In my garden, they are very fond of strong, pithy stems like raspberry canes, tall asters, perennial sunflowers, and goldenrod, and also some hollow stems like monarda and agastache. Just try some different things and see what they like.
The stems can be vertical or horizontal. They use both in my garden, but yes, they should not be lying in the mud. I even made some small carpenter bee hotels out of bundles of raspberry canes, and the bees loved them, but having them bundled together in one spot like that also made it easy for tiny parasitoid wasps to find them, so that’s not such a great idea. Better to have nesting opportunities scattered throughout your garden.
I can write an article on this for Garden Rant if you’d like.
Please write an article with this information. This is the first time I have ever heard this information and this method is so much more appealing to the average gardener. I think more people would be willing to do this method to help our bees
Yes, please, write an article with this information! I’ve done a little bit of everything — cut back at different lengths, cut back and left at the edge of our woods — but would love to have a better idea of what the best methods are.
Yes indeed! I’ll email you about a guest post.
On the aesthetics of rebar: I like rebar in the garden. It rusts nicely. And as Jack Wallington pointed out on his blog a while back, it never needs to be replaced.