This rather brutal sounding colloquial term creates imagery of Sweeney Todd, the Demon Barber of Fleet Street in my head, rather than the somewhat gentler pastime of gardening. So, let’s get back to the more precise and descriptive term of mid-season formative pruning.

The Chelsea part refers to the timing, as the Chelsea flower show is held traditionally at the end of May and this type of pruning is usually undertaken at the same time or just after, depending on the weather and subsequent growth of plants that flower after June.

Reason: Some herbaceous perennials, that flower later in the year, tend to grow much longer stems and these are inherently weaker than shorter stems. By shortening these stems, you will encourage the plant to send out side shoots which will give you a bushy compact shape that is far more capable of holding itself up without the need for staking. The production of all the extra side shoots means that the plant will be able to produce many more flower buds and give you a superior display. The flowering will only be pushed back by a couple of weeks and this can also extend the season of interest for you. The flowers may be slightly smaller but there will be many more of them.

Some plants that respond well to this treatment are:

Agastache Genus - Agastache (hardysplants.co.uk)

Ageratina Genus - Ageratina (hardysplants.co.uk)

Alstromeria Genus - Alstroemeria (hardysplants.co.uk)

Anisodontea Genus - Anisodontea (hardysplants.co.uk)

Aster Genus - Aster (hardysplants.co.uk)

Boltonia Genus - Boltonia (hardysplants.co.uk)

Chrysanthemum Genus - Chrysanthemum (hardysplants.co.uk)

Dahlia Genus - Dahlia (hardysplants.co.uk)

Echinacea Genus - Echinacea (hardysplants.co.uk)

Eurybia Genus - Eurybia (hardysplants.co.uk)

Eutrochium Genus - Eutrochium (hardysplants.co.uk)

Filipendula Genus - Filipendula (hardysplants.co.uk)

Helenium Genus - Helenium (hardysplants.co.uk)

Helianthus Genus - Helianthus (hardysplants.co.uk)

Hylotelephium (formerly Sedum) Genus - Hylotelephium (hardysplants.co.uk)

Inula Genus - Inula (hardysplants.co.uk)

Knautia Genus - Knautia (hardysplants.co.uk)

Leucanthemella Genus - Leucanthemella (hardysplants.co.uk)

Penstemon Genus - Penstemon (hardysplants.co.uk)

Phlox paniculata Genus - Phlox (hardysplants.co.uk)

Rudbeckia Genus - Rudbeckia (hardysplants.co.uk)

Salvia (in particular those that originate from South America) Genus - Salvia (hardysplants.co.uk)

Solidago Genus - Solidago (hardysplants.co.uk)

Symphyotrichum Genus - Symphyotrichum (hardysplants.co.uk)

Veronicastrum Genus - Veronicastrum (hardysplants.co.uk)

Usually the plants are cut back by a third or up to a half, with the cut being placed just above an outward facing bud or leaf.

You can also extend the time over which you plant flowers, by cutting only the front third or half of the plant in this way. You will then have the plant flowering at its normal time and height and the second half flowering later.

If you are nervous about doing this for the first time, you could cut back one stem in three and take some of the stress out of the decision. When, just a few weeks later, you see how well the plant has responded it will give you the confidence to go for it, next year.

Happy pruning.