A perennial plant dies back to the ground every fall and grows from existing roots each spring. The longevity of each perennial differs with some being as short as 3 years while others last over 100 years. Transplanting or dividing these plants should be done in the early spring or fall. At this time the year, the temperature is cool enough to ensure minimum damage, while the ground is still warm enough for new roots form.
Not all perennials need to be split but many will benefit from the procedure. Plants exhibiting the following characteristics should be split.
Plants that produce fewer, and smaller flowers than usual, will benefit from division. Once split into smaller sections the plants will develop new vigor.
When a plant outgrows its designated area and starts crowding other plants, part of the plant needs to be removed allowing the plant to continue to grow. Often plants left unchecked can take over a whole flower bed.
Perennials will start to die out in the center but still have green and productive growth on the edge. If the dead material isn’t removed from the plant, the whole plant will become spindly.
Plants don’t have to be showing signs of stress before they can be divided. They are often split because more than one plant is desired. As most perennials grow quickly it is a practical and economical, way to produce more plants.
The root and plant structure dictate how to divide a perennial so examine the plant carefully before starting.
Plants with bulb roots need to be dug up and carefully separated by hand. When replanting the bulbs, keep in mind that the larger bulbs produce the best flowers. Very small bulbs might need a few years to develop before flowering. Lilies and all spring flowering bulbs are best planted in the fall.
Plants with underground runners that come up some distance from the mother plant are called suckers. When digging up this new growth, make sure some fine roots are growing from the sucker stem, before severing the connection with the mother plant.
Thick roots called rhizomes need to be dug up and carefully separated. If they have grown into a tangle, carefully cut the roots apart using a sharp knife, ensuring that each rhizome has at least one bud or shoot. The roots of Irises and Lily of the Valley are rhizomes.
Plants that spread by producing new crowns, in an ever expanding circle, usually need split every 4 or 5 years. These plants should be dug up and split into a number of pieces. To grow, each new plant requires a few stems and a good supply of roots. If the center of the root is dead, remove all the dead material which should result in a number of individual plants remaining.
Ground covers and low growing plants are the easiest to split. They often produce roots at nodes, where their stem touches the ground. All that is needed to propagate these plants, is a sharp knife to separate the offshoot from the mother plant. In the spring it is often possible to propagate these plants by burying pieces of the plant in soil with or without roots.
When dividing plants, only replant healthy material. Discard any material that is damaged or diseased.
To replant, dig a hole, put in bone meal and fill it with water. Once the water has receded, place the plant in the hole and back fill with soil, pressing it down firmly around the plant. Try to place the plants at the same depth as before as this affects some plant’s growth habits. Give away any perennials that don’t fit in your garden.