Do you know why the flower went to the dentist? It needed a root canal.
Flowers don鈥檛 need dentists, of course, but humans do come in handy for other flower tasks. For example, most perennials thrive from being dug and divided occasionally, and spring is the preferred time for many types.
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How do you know if perennials need dividing? If the center of the clump is bare and all the healthy growth is around the outer perimeter, the plant benefits from being dug and cut into sections and the healthy portions replanted.
If the perennial is no longer blooming the way it once did, dividing can reinvigorate the plant. Dividing perennials is also an effective way to propagate them, creating plants to share with others or expand the perennial bed.
Some perennials need dividing more frequently than others. Every two to three years, divide monarda, carnation, coral bells, delphinium, tall garden phlox, chrysanthemums and dianthus.
Every three to five years, divide astilbe, campanula, coneflower, daylily, lily and iris. Every five to 10 years, divide hosta.
Long-lived perennials like peony, bleeding heart and gas plant can remain in place for many decades as long as they are flowering abundantly.
Some perennial types don鈥檛 like being divided at all, including baby鈥檚 breath, Asclepias butterfly flower and Russian sage. Offshoots can be dug, but the original plant prefers to remain intact.
Some perennials are best divided in spring, and others in fall. Keeping them straight is easy if we remember one rule: divide perennials during the season opposite their bloom time.
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For example, if perennial types bloom in spring or early summer, such as tulips, peonies, iris and bleeding heart, fall is the recommended time, usually in September.
If perennial types bloom in mid-summer or fall, then spring is the recommended dividing time, including hosta, tall garden phlox, daisies, monarda, chrysanthemum, sedum, ornamental grasses and many more.
Late April is a perfect window of opportunity to divide types that prefer spring division. If possible, wait until new growth is just beginning to emerge from the ground. At that stage, it鈥檚 easy to distinguish parts that are alive and will make better divisions.
If we delay too long and the plant becomes full-grown with fully developed leaves, division greatly disrupts the plant and its root system, causing greater transplant shock.
Following are the steps for successfully digging and dividing perennials in spring:
- Digging and dividing perennials is easier if the above-ground, dead tops that were left during winter are now removed, cutting the old stems down to about an inch above soil level. If new growth has started to emerge from ground level, take care not to interfere with the tender new plant shoots.
- With a spade or garden fork, begin digging around the perennial鈥檚 perimeter, going down about the depth of the spade鈥檚 metal or the fork鈥檚 tines. Rooting depth and mass vary greatly with perennial type.
- Lift the entire clump out of the soil. With a sharp knife, saw or spade, cut down through the clump. The number of divisions will vary by the size of the original clump, but nearly all perennials can be divided into at least four divisions, sometimes six or eight.
- Don鈥檛 allow roots to dry out. Roots can quickly die if exposed to air for more than a minute or two. Wrap roots in moist burlap or plastic and replant quickly.
- This is a great opportunity to incorporate additional organic material, such as compost or peat moss, into the planting hole, which almost all perennials love.
- Install perennial divisions at the same depth as they were originally growing. Groupings of three or five divisions create visual impact. Space appropriately, depending on the mature width of the perennial being divided.
Plant the division at the original depth and water well. Chris Flynn / The Forum - Water each newly planted division, which rehydrates the roots and settles the soil around the root system.
- If desired, apply shredded bark or other mulch around the perennials.
- Water-soluble fertilizer applied at planting time and again in May and June will provide nutrition for substantial growth and strong bloom. Depending on the plant size, most new divisions could use 1 to 2 gallons of fertilizer solution.
- If divisions were small or medium-sized, keeping flower buds removed during the first growing season allows all the energy to go into establishing the perennial for better bloom long term.
- Label each division using weatherproof material, if the cultivar is known.
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