Fall is a great time to rejuvenate the garden by dividing spring-blooming perennials. The plants will be healthier and bloom more next spring plus you get the added benefit of having more plants to fill in the bare spots.
Healthy plants grow new roots and shoot every spring and summer. If they are not divided, they compete for sun, airflow, nutrients and room in the ground.
Perennial roots grow during the winter months and ideally, all the replanting will be completed a month before the ground freezes.
Water the soil the night before. After digging, the roots can be soaked in a tub of water to remove the soil. Sometimes even soaking is not enough and the roots have to be pruned in order to separate the clump into planting-size pieces. Use a sharp, clean tool to make the cuts. Tool blades can be dipped in 10 percent chlorine bleach solution or white vinegar to kill any fungus on the blades.
Fast-growing plants such as false spirea, astilbe, separate easily. Cut through the roots with a sharp knife to make clumps to replant into prepared holes with soil amendment.
Beebalm or monarda clumps can be dug, cut into sections and replanted for next summer’s butterflies.
Daylily, hemerocallis, clumps can be easily separated in the fall. Insert a shovel blade or two pitchforks into the ground 6-inches from the root ball. Then, wiggle the tool back and forth to get a clump of root. The shoots tend to do better if a few are planted in the same planting- hole.
Bearded iris can be divided and replanted from late summer to late-fall. Dig them up and separate the corms. Discard the green tops and the rootless mother corm in the middle of the clump then apply liquid or powder fungicide. Plant each corm in compost-amended soil, with the top showing.
Coreopsis, tickseed, should be divided every fall to keep the plants healthy and blooming. Soak the roots to separate, discard any weak center parts and plant the divisions a few feet from each other.
Geranium or cranesbill is root divided every 2 to 4 years to keep the clumps of roots healthy.
Hostas can be divided to fill in the bed, too. Three year old plants are dug, and then the roots are soaked to remove the soil. Gently wiggle the individual eyes out of the clump and replant in loose, moist soil. One easy method to rejuvenate large Hostas is to remove a wedge from the plant. Replant the wedge and the existing plant will fill in the bare spot by spring.
Lambs-ear, Stachys byzantine, should be divided every 2 or 3 years to prevent rotting. After digging, remove the center weak parts and replant the outer pieces.
Peony roots are divided into separate eyes in September. A clump of 3 to 5 eyes is planted no more than one-inch deep. It can take two years for the new plants to bloom.
Phlox should be divided every two years to keep it blooming. Prune the plants to no more than 8-inches tall and dig a group of roots, shaking off the soil. Use a sharp shovel to cut the clump into quarters. Replant in a sunny bed.
Cone-flower, echinacea, rudbeckia, is divided every 4-years.The roots are dug, divided and replanted as above.
Red-hot-poker, kniphofia, does not have to be divided but can be in the fall to increase the plants in number. The new plants will need 2 or 3 years to re-bloom.
Yarrow, achillea, will die in the center if the clumps are not divided every couple years. The spreading roots are cut into divisions and replanted.
For illustrated, specific directions see http://bit.ly/1ap1tSo.