Dividing and transplanting perennials is recommended every few years to refresh blooming and give the plants adequate growing room. Many are long-lived so, over several seasons, crowding occurs. This is when they need to be divided and transplanted or spaced out. With more growing space, the invigorated plants gain better air flow and more light.
It is recommended to divide most perennials every three to four years, or when growth and blooming are noticeably decreasing. In certain cases you may notice the mother plant, usually in the center of a cluster, beginning to show signs of weakening and dying.
Autumn is the best time to divide most herbaceous perennials because the soil is still warm enough to stimulate new root growth. Also the season’s cooler air lessens the shock created when the plants are split apart and uprooted.
Among plants that are commonly grown in our area and require periodic division are: Gaura, Penstemon, Catmint, Day Lily, Society Garlic, Mexican Purple Sage, Candelilla, Ruellia, Iris and Artemisia.
Healthy bulb plants that should also be divided every few years include: Rain Lily, Freesia, Spider Lily and Amaryllis.
When preparing to divide, first thoroughly water the plants. This will aid with digging and separating. Using a sharp-edged shovel, dig around and beneath the cluster, a few inches beyond and down to 10 to 12 inches deep. After thusly freeing the plant, carefully lift it from the soil.
Next, gently separate the newer individual plants with your hands. Tight clumps may make it necessary to use a spade or tool to force division. Discard any weak or damaged pieces, transplanting only healthy, robust plantlets. Before planting, add a high phosphorous (second number on the bag) fertilizer into the prepared planting holes.
Be certain to set the transplants at the same level in the soil as they were originally growing. Covering the plant crown with soil may cause stems to rot. Do not crowd; leave adequate space for future growth.
Next, add 2 to 4 inches of clean mulch around the transplants to help retain moisture and to insulate the roots from coming cold. Be sure to keep the soil evenly moist but not wet during late fall when the plant is developing.
Perennial division and transplanting is a simple and inexpensive method to gain additional plants for your own garden, or for sharing with friends and neighbors.
Mary Kidnocker is a University of Arizona Master Gardener who lives in the Green Valley area. Her articles are featured weekly.