Recently I was asked by a Highfield Gardener how to keep the fall blooming Montauk Daisy from flopping over. It has been my experience that when left on their own they do indeed tend to collapse when in full bloom. This can be controlled by a bit of timely pruning to keep the plants shorter and encourage stronger stem growth.
In late fall, when the plants have shut down and turned yellow, I cut them down to three or four inches above soil line. The more significant cut happens in mid- to-late May when I remove one third of the height of the new spring growth.
Pruning back summer flowering perennials at this time is referred to in the gardening world as the “Chelsea chop” because it corresponds to the dates of the Royale Horticultural Society Chelsea Flower Show in London, England.
The Chelsea chop delays flower time a bit so the bloom time of many multi-stemmed perennials can be extended using this technique. Cutting back the height of one third to one half of the stems on individual plants results in a longer flowering season for the plant.
If you have more than one plant of the same variety, it is good to cut back some plants and leave others alone. Perennials that respond well to the Chelsea chop include tall phlox, achillea, aster, echinacea, rudbeckia, helianthus and sedum.
Be careful not to use the Chelsea chop on perennials that flower only once or for a short time such as lilies, aquilegia and peony. Put the Chelsea chop on your gardening calendar and we will review it again next May!