Pruning Perennials - The Chelsea Chop
By Cathrine StClair
Have you heard of the Chelsea Chop? It’s a pruning technique that can be used on herbaceous perennials to manipulate the size, influence bloom time and prevent flopping of taller plants. It gets its name from the famous British Chelsea Flower Show which takes place at the end of May – about the right time to do this pruning. And the technique is pretty much a straight on “chop”, so the name really fits.
The idea is to simply cut back vigorously growing perennials by a third or half. This cut back done in late spring to early summer will cause the plant to side branch at each cut stem. The resulting plant will be shorter, bushier and less prone to flopping than if left un-pruned.
Generally, it will also flower a little later in the season and have more numerous flowers – but each individual flower will be smaller (which can also help to prevent flopping).
Goldenrod before trimming in May
An example is this Goldenrod (Solidago rugosa ‘Fireworks”) in my back garden. I plant my drifts of plants close together because I like a full look and weeding and mulching are not my favorite activities. If I let this stand of Goldenrod grow all season, it will become so tall and wide that it will impinge on the Phlox and the Aster growing on either side of it.
Goldenrod after a quick shearing with hedge clippers
So – around the end of May, I just take my hedge sheers and chop it in half. It will proceed grow over the season and flower in September, just as the Phlox is finishing its flowering and the Aster is about to start.
Tall Sedum in bloom
Another “chop” technique is to cut back only the front or outer edges of a grouping instead of the whole thing. The shorter, denser cut stems will help hold the taller un-cut stems upright. The un-cut stems will flower first, followed by the ones that were chopped – extending the bloom period of the planting. I use this technique with tall sedums which often flop open in my clay soils.
Of course, not all perennials are candidates for “chopping”. Plants with single buds like Peony, Lily or Iris will lose their flowers if chopped. It works best on summer-to-fall blooming plants, because early bloomers may not flower at all if chopped. Also, if a plant is stressed by disease or drought, chopping will add to that stress and may weaken or even kill the plant.
Some great candidates for the Chelsea Chop include:
Black-eyed Susan (Rudbeckia)
Catmint (Nepeta)
Garden phlox (Phlox paniculata)
Goldenrod (Solidago)
Joe Pye Weed (Eutrochium)
Native Aster (Symphyotrichum)
Obedient Plant (Physostegia)
Penstemon (Penstemon)
Shasta daisy (Leucanthemum × superbum)
Sneezeweed (Helenium)
Upright sedum (Hylotelephium)
Yarrow (Achillea)
Experiment a bit with the “Chelsea Chop”. It can really enhance a planting and reduce maintenance.