How to Divide Herbaceous Perennial Plants
Separating Lilies, Iris Bulbs and Other Perennials
Nov 5, 2008
Perennial plants often grow larger year by year, and with bulb flowers with running rhizomes like irises, lilies, lily-of-the-valley plants, and many others, the clump of plants can increase in size year after year. For plant health, division is an important part of fall or early spring maintenance.
While many woody perennials and shrubs to not need to be divided, herbaceous perennials and herbs often do well with division. Check out the Plant Encyclopedia for information on specific plants to see whether division is suggested.
Choose Plants Ready for Division
First year perennials are often too small to be divided and separating a small plant will cause too much stress. In the first picture below, gardeners can see a large, overgrown clump of heirloom lilies ready to be divided. Note how closely together the individual plants are to each other.
Prepare the Plants to be Divided
To prevent transplant stress it can be beneficial for gardeners to water the perennials deeply the day before division. Choose an overcast day or do the transplanting and division in the evening when the sun is not shining too brightly.
Dig Up a Large Clump Around the Plant or Plants
Gardeners will want to use a shovel large enough to dig around the plants without hurting too much of the root system. Dig deeply enough to preserve the largest roots of the perennial.
Separate the Individual Plants Carefully
Work carefully to pull apart the roots of the plants and cut away any connecting roots. If gardeners are dividing one, large plant they should use a sharp shovel or knife to slice the crown of the plant, or root ball mass, in half. Many bulbs, rhizomes and perennials that spread via runners, can simply be detached from each other leaving two individual plants.
Replant One Section of Plant in the Old Space
When landscapers are dividing a large herbaceous perennial, such as a hosta, they will often replant one of the newly divided sections back in the original planting space. In the case of the heirloom lilies shown below only one plant was replanted in each square foot, leaving plenty of new starts to plant elsewhere, or share with fellow gardeners.
Transplant the Other Plant Sections
The newly cut sections of the perennial plant, or individually separated small rhizomes, bulbs or plants can now be transplanted. Gardening swaps are a popular place to share these newly divided plants or landscapers can use them in other garden locations.
Choose the Time of Year To Divide
If gardeners are dividing a plant that blooms in the spring or early summer it is usually best to divide the plant in the fall after the blooms have faded. If the plant being divided is one that will bloom in the fall months, landscapers will usually divide in the early spring just as new leaves are beginning to show through the soil.
Many perennial plants only need to be divided every 3 to 5 years, but others can be divided more often depending on the rate of growth. Plant division is an easy way to increase the number of plants in a landscape or garden area.
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