Divide and Conquer Your Perennial Border
(This article was first published in The Gateway Gardener April 2010 issue)
By Steffie Littlefield
Have you noticed the flowers are smaller on some of your perennials? Or does a plant or two just look like a wad of stems and foliage all tangled up or does it have a void spot in the middle like a monk’s bald spot? What if you have a great plant but it is overtaking the whole perennial bed. These are all signs that it is time to divide and conquer. Well you are in luck because spring is a great time to divide most perennials.
Not all perennials need this special treatment every year, in fact most are happy without being brutally cut up for 3-10 years. But if you have coreopsis, phlox, dianthus, artemisia, gooseneck loosestrife or shasta daisies you may be sharing more plants than you are keeping in your garden. However if baptisia, asclepias, peonies, helleborus, carolina lupines, Russian sage or hardy hibiscus are the mainstays of your garden you may not need to rework the bed for 10 years or more.
Even if you thought spring blooming perennials should be divided in the fall and fall bloomers in the spring, spring is still a good time to lift perennials. Breaking them into useful size divisions early gives them the whole growing season to recover and become strong and vigorous for the following spring. The exceptions to this would be peonies, Siberian iris and oriental poppies which truly prefer fall dividing. Most plants do not divide well in the summer except for bearded iris which are best divided in August. The toughest perennials like hostas and daylilies are likely to do well being divided any time of the year.
Ideally spring divisions are made when the new growth is less than 4 inches high. The best plan is to lift the whole plant out of the ground onto a tarp and gently pry apart, cutting some of the roots with a clean sharp knife. Leave 3-5 growing tips or eyes on each division and then replant one of these divisions in its place adding new compost and bone meal or Pro-Start fertilizer to encourage strong new root development. Woody root systems may require the double fork method where two forks are inserted back to back in the tangle of roots in order to pry to them apart. When you can’t dig the plant out of the ground it is acceptable to at least remove portions of it from the crown to open up the growing space. Fill in the holes with new soil and compost.
All these lovely divisions can be used in other gardens shared with friends, and you may find room in your perennial border for the newest selection of plants that you’ve been eyeing at your neighborhood garden center. So clean-up, dig-up and cheer-up that old perennial bed, as you divide and conquer this spring.
Steffie Littlefield is a horticulturist and garden designer at Garden Heights Nursery. She has degrees from St. Louis Community College at Meramec and Southeast Missouri State and is a member of Gateway Professional Horticultural Association and president of Horticulture Co-op of Metropolitan St. Louis.