Seasonal Deadheading Decisions: Deadheading Works on Some Flowers Better than Others, but Timing is Everything

Southwest Yard & Garden by Dr. Marisa Thompson

Deadheaded marigolds produce more flowers, but only if cut early enough in the season. Photo credit M. Thompson.

Question: Does deadheading marigolds encourage new flowers?

-        Jeannie O., Truth or Consequences 

Answer: I’ve often wondered this myself. Many flowering plants, like coreopsis, roses, yarrow, catmint, and marigolds respond very well to deadheading and are worth the effort. Others, like portulaca, begonias, and impatiens, may not need deadheading because their flowers just fall off naturally or the new flowers conceal the old. I had trouble finding lists of flowers that should never be deadheaded. It is more crucial to watch the calendar. If the second flush of flowers will have time to develop and bloom before frost, deadheading may be a good idea. As Dr. Curtis Smith, retired NMSU Extension Horticulture Specialist, pointed out when I asked for his input earlier this week, “Our summer annuals and our perennials are going to die soon when frost arrives, or go dormant, so deadheading them now is not really necessary.  In Central and Northern New Mexico, the newer flowers will not have time to set seeds anyway.”

The decision on whether to deadhead also not depends on your end goal. If you want annual flowers, like marigolds and zinnias, to reseed themselves, letting some or all go to seed makes sense. If you’re trying to control what comes up in your garden bed next year, clipping the flowers before they set seed will help. I want bright desert marigolds to take over in my yard and at work, and they already bloom for such a long time without any added water. So instead of trying to deadhead them, I just grow with it. Note: Desert marigolds (Baileya multiradiata) are native in the Southwest and are a different species than the marigolds commonly sold in garden centers (Tagetes spp.), which are mostly native to more southern areas of Mexico, Central, and South America.

If you want your desert marigolds to reseed, skip the chore of deadheading all together. Photo credit M. Thompson.

Deadheading is a pruning technique for encouraging a second bloom and involves removing spent flowers by cutting the stem. Lots of bare flower stalks can look ugly, so if I’m taking the time to deadhead, I usually make the cut lower on the stem so the cut edge is hidden by foliage. On the other hand, Dr. Smith made some great arguments for leaving a longer stem: “If you can deadhead by snapping off only the flower, leaving the stem, that stem, being green has chlorophyll and is photosynthesizing, so it will continue to produce food for the plant until it turns yellow and dies back.  Some people do not like to leave the stems exposed, but late in the season, that extra photosynthesis may be helpful.  At any season, leaving the flower stalk to photosynthesize and then die back on its own allows the plant to draw nutrients and carbohydrates from the stalk as it dies back.”

The idea behind deadheading is that seed development requires a lot of energy. So if it’s the flowers you’re after, removing old flowers as soon as they start to decline helps the plant put that energy into new flowers instead of setting seed in the old ones. Flowering varieties that don’t set seed, like some verbenas and lantanas, don’t need to be deadheaded at all.

It’s too late to deadhead zinnias now and get new blooms, but cutting flowers earlier in the season can really increase flowering time and number of new blooms. Photo credit M. Thompson.

When deadheading, be careful not to cut below unopened, hidden buds. Zinnias, and many others, often have new flower buds developing lower on the stalk, so I’m careful not to accidentally take off too much and remove that second flush of color accidentally.

Deadheading can be a chore, but if you get comfortable it can be relaxing, and if done at the right time, and on the right plants, the extended bloom time is ample reward.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.