Deadheading summer phlox (Phlox paniculata) is a good example of how even within the same species plants can behave very differently, and our treatment of them might need to vary as well. In mid-August the plants that came into flower in July are beginning to either slow down or go by, so clipping the old flowers off can improve the appearance of the plant. For some varieties of phlox it can stimulate new flower production, but not for all. Here are some examples.
To deadhead phlox you clip just below the declining flower or seed heads.
This is a phlox called ‘Blue Paradise’ – it’s an interesting plant because in the early morning the flowers are very purple-blue, but when the sun hits them they turn pink.
Although the plant is cleaned up a bit after ‘Blue Paradise’ is deadheaded, it doesn’t usually produce side shoots and more flowers. As long as the foliage is attractive I leave it in the garden but when the leaves decline more from the leaf-spot that’s brewing, I’ll just go ahead and cut the plant down to the ground. So this is a Phlox paniculata that won’t flower again when deadheaded.
The phlox in the Volcano series from Tesselaar Plants put out strong new growth if they are deadheaded promptly. Even in a bad mildew year, when this plant does get some powdery mildew, this Volcano Pink With White Eye produces clean new growth that will produce a good new head of flowers.
Here is a Volcano Purple With White Eye Phlox that has been deadheaded about two weeks ago. You can see that this plant is already growing new leaves and buds. In late August this plant puts on a huge new show of flowers. In my gardens the Volcano Phlox are best at repeat flowering after deadheading.
This is an unknown phlox (Lavender David?) in the garden by my shed. It is reliably mildew-free every year and I clip the individual flowers as they go by rather than waiting for the entire plant to need deadheading. Sometimes I use this plant for cutting flowers as well. This plant produces some side shoots that bloom in response to deadheading, and the foliage remains attractive even if the amount of secondary bloom isn’t as prolific as it is on the Volcano series. So in general this plant is an asset in the garden even after peak bloom.
Just with the four varieties of summer phlox shown you can see tremendous variations in how the plants respond to deadheading. One of the pleasures of gardening with perennials is getting to know the plants as individuals.