Fall is a great time to divide spring and summer blooming perennials. As long as you finish the task before freezing weather sets in, autumn is the best time to divide spring and summer bloomers because it gives them time to reestablish strong root systems before the flowering cycle begins again in spring or summer.
Most perennials need dividing because they grow outward from the center causing the middle of the plant to wear out over time. You can tell it’s happening when the plant becomes less vigorous, begins blooming less, and dies out in the center. Even if your plant is vigorous and healthy you still might want to divide it in order to start over with a smaller plant if your perennial has grown too big and is smothering nearby plants, or if your neighbor is begging you for a piece of a prize perennial to plant in his or her yard.
Some perennials need dividing more often than others. Achillea (yarrow), Anchusa (bugloss), Campanula (bellflower), Crocosmia (montbretia), Hemerocallis (day lily), Siberian Iris, Lobelia, Monarda (bee balm), and Phlox are spring and summer perennials that generally bloom more reliably if they are divided every 1 to 3 years. At the same time some spring and summer flowering perennials are difficult to almost impossible to divide and are better left undisturbed.
Actaea (bugbane), Aruncus (goatsbeard), Gypsophila (baby's breath), Eryngium (sea holly), and Platycodon (balloon flower) have woody rope like roots that tend to break easily causing severe dieback when divisions are attempted. Others such as Aconitum (monkshood), Aquilegia (columbine), Euphorbia (spurge), and Pulsatilla (pasque flower) simply resent root disturbance and show their displeasure by going into major decline.
Fortunately, these perennials rarely die out in the center or stop blooming with age. Give them room and enjoy the fact that these perennials will thrive with little or no effort on your part, but visit the nursery to buy new ones if you want more of them.
Dividing most spring and summer blooming perennials is straightforward. Begin by cutting the stems back to the ground to make it easier to pull or cut the roots apart without having to deal with tangled foliage. Then dig and lift the clump. When cutting the root mass into sections, look for natural divisions and take sections from the vigorously growing edges of the root mass while discarding the bare middle. If sections can be easily teased apart, simply use your hands to pull off pieces from the edges. If, on the other hand, the roots are thick and hard to break, it might be necessary to use a sharp knife or an old pruning saw to cut off sections. Most of the time I simply thrust my digging spade through the roots to slice off a healthy chunk of roots from side of the root ball. Always work compost and organic fertilizer into the planting hole before you replant the divisions.
By the way, it never hurts to remind your neighbor how much you love chocolate chip cookies when you give him or her a division.
Segment Producer Suzie Wiley. Watch New Day Northwest at 11 a.m. weekdays on KING 5 and streaming live on KING5.com. Contact New Day.
