Most of us instinctively know that we need to cut back many perennials after their blooms are spent. However, many perennials benefit from an early cutback, before the flowers appear. Now that the garden is preparing for autumn, it’s time to take stock of your garden. Look at it objectively to discern what works—and, more importantly, what doesn’t.
Because I dislike staking plants, I am not fond of those plants that flop, sometimes from the weight of a good rain or due to the heaviness of their blooms. It is in the fall that I use that memo app on my computer to note those plants that require a good clipping in May if they are to remain upright during the growing season.
I have a nameless, very tall coreopsis, which I enjoy for its August blooms. However, it is a leggy creature with spindly stems that seem incapable of supporting great heights. Consequently it acquires an unattractive droopy appearance. I have now learned that if I cut it back by a good third in May, it will become a shorter plant whose stems can support its many flowers.
Sedums fooled me for years. They remain sedate, rather prim looking creatures actually—until they proceed to grow two feet overnight. By the time ‘Autumn Joy’ blooms, it is a messy looking, sprawling plant that offers little to the fall garden. Now I know that if I cut it back in May, it will look downright perky come late August, resembling a tidy plant that looks as though it comes from a nice family.
Leucanthemum x superbum ‘Becky’ also profits from a late spring shearing, leaving stems strong enough to withstand the power generated by a thunderstorm. I love daisies when they are upright but resent them when they insist upon a horizontal position.
These are perennials that bloom on new growth, so cutting them back in May will produce shorter, stronger plants with the flowers appearing perhaps a week later than they normally would.
However, this method doesn’t work for dahlias, which produce large, heavy flowers their stems cannot support. Staking dahlias is not fun (an understatement). Last fall I made a note to buy tomato cages for the dahlias in the early spring. When the leaves appeared in May, I placed the tomato cages over them, training the dahlias to grow within the confines of the cages. No, for a month it wasn’t a great look but dahlias grow quickly and soon the tomato cages were virtually invisible—and the dahlias remained upright. I can handle the sight of homely tomato cages if it means I don’t have to stake dahlias later on.
Amsonia hubrichtii is a wonderful plant that produces lovely blue flowers in the spring. However, by the end of May it has grown so big that a good rainfall will cause it to dramatically droop. Rather than try to prop up the stems, I cut it back by almost half; it quickly regrows, casting a brilliant chartreuse halo of new growth that is quite pleasing.
By making these notes in the fall, I am reminded of what I need to do in the following spring—tasks that aren’t readily apparent in May when plants look deceptively innocent. This year my Nipponanthemum nipponicum—aka Montauk Daisy—is looking awfully leggy. Rest assured, it’s on my list to get a good shearing next May.
Byline
A serious gardener for the past twenty years, Kit Flynn resides in Chapel Hill. She is also a Durham Master Gardener.