Why prune perennials? The reasons abound, from improving floral abundance and/or size and reducing unwanted spreading to cutting down on mildew diseases, preventing flopping and lengthening bloom time. But pruning is not a one-size-fits-all strategy and depends on the plant in question, as well as the desired outcome.
When size matters, remove the side shoots as they appear. This forces all the energy into producing one big major bloom at the stem tip. Dahlias, roses and peonies respond well to such disbudding.
Conversely, to increase the number of flowers and lengthen the number of blooming days, deadhead, or remove dead flowers, the central flower stalk once it is finished. This encourages the lateral buds to develop and bloom. Butterfly bush, a prime example, blooms on and on, providing a food source for pollinators.
Some perennials become garden thugs, reseeding left, right and center. To prevent plants like rose campion (actually a biennial) from becoming a nuisance, lop off the seed heads after blooming is done but before they open and distribute their seeds. You can cut off individual seed heads as they ripen, or if you have plants that bloom at the same height, trimming off multiples with garden shears goes faster. Either way, be sure to remove the fallen seed heads from the garden.
See more: Tips for the Aging Gardener
Pruning Perks
For plants prone to mildew and bacterial wilt diseases, the aim of pruning is to open up the clump of plants, which increases the air flow. Moving air allows the plants to dry out faster following rain and morning dew, making it harder for moisture-loving diseases to become established. Once the plant is up and growing in the spring, remove several of the interior stems, cutting them at ground level.
Mums, autumn joy sedums and asters tend to grow really tall and top heavy, split and then droop over, leaving gaping holes in the side of the clump. Never fear, a pruning solution exists. Cutting them back by one-half or one-third in early summer removes the growing tips and results in a shorter, compact plant so covered in blooms it’s hard to see the green stems or leaves underneath. Most clumping perennials respond with a bushier habit whenever you remove the growing tips. Stop trimming by July so the plant has time to set buds and flower before the growing season ends.
By now, you’ve probably gleaned the most useful information about pruning perennials. They, and most annuals, will continue to bloom in an effort to disburse seeds. If thwarted, they keep on trying.
See more: 7 Pollinators to Help Your Garden Grow
Ask the Expert
Q: We removed a tree five years ago and ground the stump. Now the ground is sinking in various spots in that part of the lawn. What can we do?
A: The tree roots are decomposing and soil is sifting down into the empty spaces. It will continue for several years. Meanwhile, you can remove the grass and make an annual garden. Stick a long-tined garden fork into the depressions and wiggle it to settle more soil. Fill with dirt, level it and plant away. Using annuals lets you repeat the process each spring until the depressions stop appearing.
