Prune in June: it’s a good time to pinch back tall or floppy perennials like these chrysanthemums. Photo: http://www.wilsonbrosgardens.com
Are you finding your late-blooming perennials floppy and maybe just a bit too tall for their own good? If so, you can often fix it by cutting them back hard in early summer. This forces the plant to grow new stems, but they won’t be as tall the second time around. Also, there’ll be more stems and therefore more flowers.
This type of pruning is actually called pinching, although it’s a lot harsher than you’d imagine pinching to be. Usually, you’ll be cutting the plant back by a third or even half. And not necessarily between your thumb and forefinger. If the stem is tough, you’ll need pruning shears.
I actually use a weed-whacker (string trimmer) to pinch perennials: it’s much faster than pinching individual stems.
The downside to pinching perennials is that this will also delay flowering by two to three weeks. Sometimes the resulting flowers are a bit smaller too, but the increased number of flowers more than makes up for that.
A Pinch in Time
You need to time this right. Usually early to late June is fine in cooler climates, mid-May to mid-June in mild ones. Don’t try this too far into July, though, as by then the plants may already be producing flower buds, although they could be microscopic at this point, and won’t have time to produce new blooms before frost gets them.
This is a classic treatment for chrysanthemums (Chrysanthemum morifolium), floppy autumn stonecrops (Hylotelephium spp, formerly Sedum) and those insanely tall fall asters (mostly Symphotricum novae-angliae and S. novi-belgi), but also for the following:
- Beebalm (Monarda)
- Culver’s root (Veronicastrum)
- Cup plant (Silphium perfoliatum)
- Garden phlox (Phlox paniculata)
- Helen’s flower (Helenium)
- Ironweed (Vernonia)
- Joe Pye weed (Eupatorium)
- Monkshood (Aconitum)
- Nepeta (Nepeta)
- Obedient plant (Physostegia)
- Silver mound (Artemisia schmidtiana)
- Turtlehead (Chelone)
- Veronica (Veronica)
Don’t try this on perennials that won’t branch when pruned, like astilbes (Astilbe), daylilies (Hemerocallis), iris (Iris), lilies (Lilium), red hot pokers (Kniphofia) and ornamental grasses.