I did a Chelsea Chop in May (as recomm by the forum) - when the plants weren't that big. Below is how they were in July - coming back shorter and sturdier (not flopping). They are now flowering and doing really well - some just going over and some peaking (full sun, sandy soil). It's been a real pleasure to watch how they developed over the year, simple plants at the front of the bed. Snails have discovered them and have been chomping the leaves, which is a shame and the foliage is mangled.
Dividing them will certainly help - it takes a couple of years before they get to full size. Rich soil definitely encourages more soft growth. Most of mine are in front of a Hydrangea. Nice and dry, and only get later sun. They just start into growth at the same time as the Hydrangea and it supports them.
Mine are only about a couple of inches tall in mid/late May @Fire
It's a place where beautiful isn't enough of a word....
Mine that I inherited with the garden used to do this, but when we redid the garden they were moved to the top of a retaining wall and the drainage does wonders. I thin out the stems rather than chelsea chop, so the plant is less congested and there are only nice strong stems left.
Agree with @Hostafan1; they flop more on rich soil. Poor(er) and dryer soil suit them quite well. A Chelsea chop does help, you're robbing the plant of some of its all too easy investment.
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Rich soil definitely encourages more soft growth.
Most of mine are in front of a Hydrangea. Nice and dry, and only get later sun. They just start into growth at the same time as the Hydrangea and it supports them.
Mine are only about a couple of inches tall in mid/late May @Fire