“Deadhead” can mean a number of things: a fan of the Grateful Dead, to complete a trip without paying passengers or freight, or an airline crewmember hitching a free ride on a plane so they can get to their assigned flight. If you’re a gardener, then deadheading means pinching off faded flowers.
According to Gardeningknowhow.com,
Deadheading is an important task to keep up with in the garden throughout the growing season. … As flowers shed their petals and begin to form seed heads, energy is focused into the development of the seeds, rather than the flowers. Regular deadheading, however, channels the energy into the flowers, resulting in healthier plants and continual blooms.
This is what I’ve always been taught. Then I came across a post by Bec Wolfe-Thomas, on the Garden Professors Facebook blog, that disagrees:
The myth is that you need to deadhead spent blooms to get the plant to re-bloom. The theory people apply is that the plant will put all its energy into seed development and won’t bloom anymore because it no longer needs to for reproduction. This is false, plants are either genetically predisposed to re-bloom or they are not. To what degree they re-bloom also relates back to their genetics. It is a trait that plants are bred for.
She included a number of photos, of roses, fuchsias, and petunias, with both flowers and seedpods (or rose hips) on them at the same time (such as in my photo at the top of this page). Even in cases where we deadhead and are rewarded by another wave of bloom, her assertion is that the new flowers were genetically programed to happen, and deadheading was just a coincidence. For example, catmint (below) will often re-bloom whether or not you deadhead it, while bee balm (Monarda, right) won’t.
I found myself confused. Should I rush out and deadhead all the plants in my garden, as I’ve always been taught? It’s a lot of work, but it might be worth it if I get more flowers that way. Or is she right, it won’t force the plants into re-blooming, and I shouldn’t worry about it?
I decided that, for now, I’ll only pick off dead blooms that are unsightly. Brown flowers just don’t look very nice. Removing them refocuses our attention on the fresh blooms, and makes the garden look fresh and healthy.
Probably the best reason to deadhead is for aesthetic purposes, but another very good reason is to eliminate next year’s volunteers. For example, I pull my bolted cilantro the moment I see those seeds turning brown. Yes, I could save them as coriander, but I still have plenty from past years’ crops, and I don’t want cilantro all over my yard come spring. Cilantro, parsley, rose campion (Silene coronaria), and Johnny-jump-ups (left) are just a few of the plants that reseed with enthusiasm.
On the other hand, if you want to save the seeds—whether for sowing next year, winter interest, or as food for wildlife—then leave them be. You may be able to have the best of both worlds, as some plants are structured so that you can remove the dead petals but not the developing seedpod.
Annuals are the Exception
Does deadheading encourage annuals to keep blooming? The whole point of blooming is to produce viable seeds; if the gardener pinches off the dying flowers, the plant will try again. Therefore, picking annual flowers before they go to seed will often encourage more flowers, as I discovered with these basil plants.[i]) Note that many annuals, such as petunias, have been bred to keep blooming whether or not they’re deadheaded.
Don’t Prune Now
Note that deadheading only applies to dead tissue. Often, gardeners include the live tips of the branches in their pinching. This is technically pruning, and pruning definitely stimulates the plants into new growth. Early in the growing season, this is how you get bushier plants, and (for those that set buds on new growth) more flowers. You can keep petunias, for instance, from getting leggy, while promoting branching.
Pruning this late in the season is a bad idea. We don’t want our perennials and shrubs putting out new growth now. Rather, they should be hunkering down, storing resources for next spring, and in some cases, sending “antifreeze” to exposed stems and branches. Tender new growth is more apt to be damaged by cold weather, and often, our winters arrive without warning—with highs in the 70s one day, and lows in the teens the next.
As you might imagine, Bec’s post generated an extensive discussion. Were there any studies supporting her claims? Apparently, no one could find anything in the published literature. That’s likely because 1) deadheading isn’t practical on a commercial basis—and it’s commercial agriculture that funds most research, 2) journals don’t usually publish negative results , so if there was research, we won’t hear about it, and 3) you can’t prove a negative; the burden of proof is on those who say deadheading causes reblooming.
This is a terrific opportunity for a science-minded home gardener. Consider running your own experiment. Include plenty of subjects, say a large planting of ornamental salvia, and deadhead only half. Then wait and see if and how much they rebloom. Is there a difference? Finally, share your results. I’d love to hear what happens!
[i] As long as I pinch the tips of the leafy stems, basil plants respond by branching. This year, I was out of town and didn’t get a chance to tend the plants until after they had started flowering. Hoping for a bigger harvest, I carefully stripped off the fresh flowers, but all the plants did was produce more flowers, not more leaves. Similarly, removing the flower stalk from a bolted lettuce plant doesn’t encourage more leaves, or make them less bitter. Apparently, once an annual thinks it’s time to blossom, nothing will reset its biological clock.