Perennial Decision: Dead Head or Allow Seed Development?

by Marilyn Loser

2019 August 7

I’m referring to what to do about perennial flowers after they bloom.  Should I dead head (remove flowers soon after they fade) or let them develop seed heads (in order to produce future plants)? For example, if I remove faded columbine flowers, they are more likely to produce a few more flowers as we move into the fall season and the garden looks tidier.  On the other hand, if I leave the seed heeds, the tops of plants and sometimes the entire plant turns brown while producing seeds that may develop into plants next year.

“Plants flower in order to set seed. If their flowers are constantly being removed before they mature and go to seed, many plants, although not all, will simply set more. This will extend the length of the blooming season,” reports website in its deadheading article. While I’m mainly addressing perennials in this article most folks who have annuals such as petunias are aware that deadheading them throughout the summer encourages a continual bloom.

Penstemon, May night and meadow sage, purple veronica, and Missouri primrose will usually rebloom if dead headed. Some early bloomers, due to the wonderful winter and spring precipitation outdid themselves this year. The plants were taller and the flowers more abundant.  In fact, they grew so close to watering emitters, I had to trim them so the spray could water surrounding flowers.

I have plenty of purple penstemon in my best garden beds so decided to deadhead soon after the flowers faded.  As penstemon flowers bloom from the bottom up on a raceme, the bottom flowers often turn into seeds soon after the top flowers bloom.  I just cut the flowering heads off and strew them around less prolific flower beds.  My thinking is that this will provide mulch to reduce evaporation and may produce some new plants next season.  I did the same with sage and veronica.

Alternatively, I’ve removed some columbine flowers, but am letting most of them go to seed.  My reasoning is that they are in beds with other perennials that produce flowers until the end of August and the beds are really full with vegetation this year.  I will collect the seed and strew it in some of my beds and take the rest to Adam State University Seed Catalogue in the library to share with others. If you want some of my columbines, you can’t be picky about color or height!  Over many years in my garden they‘ve hybridized so you never know what color or plant height a new seed will produce.

I tend to dead head perennials the first season I plant them.  I’d rather have them put their energy into producing roots and healthy foliage rather than seeds.

A number of my perennials are taller than usual this year.  Again, I attribute it to lots of early moisture. Many columbines are 3 ½ feet tall, magenta phlox is almost 4 feet tall in one bed, and one clump of Shasta daisies is 4 ½ feet tall – chin height. 

Our garden has a lot of low dianthus plants of various colors.  The foliage is about 6 - 8 inches high and flowers bloom at about 2 inches above the foliage.  I have enough of them so I usually dead head them near the end of July and the foliage stays green until late September.  A few flowers may show up in the fall. Clumping or matting plants like dianthus as well as creeping phlox and veronicas are welcome in my garden.  They don’t require a lot of care, their growth habit deters weeds from gaining a foothold, and they tend to provide greenery until autumn freezes.

Sadly, July monsoons never developed this summer.  We had only .08 inches of precipitation last month as compared to our .97 inch average.  Make sure your plants get enough water to see them through the dry spell.

"You know you are a hard-core gardener if you deadhead flowers in other people's garden." Sue Careless