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Index : Flowers - Perennials
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- 8. Fall Is the Time to Divide and Invigorate Perennials - Top
- Perennials are soft-stemmed herbaceous plants that live for three or more seasons. Many, but not all, produce showy flowers but most have a clumping form of growth. This growth habit causes perennials to become larger and larger over time as new plantlets are produced from offsets, rhizomes, tubers, corms and the like. Over-time crowding occurs and plants need to be divided and spaced out in order to invigorate them and give them room to grow.
The best time to divide perennials is in the fall. Cool air temperatures lessen the shock to plants from being uprooted. Still warm soils are perfect for the generation of new roots on newly divided plants.
Transplanting in required on most perennials every two or three years. You can tell when division is needed because plants grow and flower less and the mother plant in the center of the clump begins to weaken and eventually dies.
Some of the perennials we commonly grow in southern Arizona which require periodic division are; Bearded Iris, Society Garlic, Cannas, Columbine, Black-eyed Susan, Purple Coneflower, Guara, Penstemon, and Artemisia. Bulbs should also be divided every few years. These include; Amaryllis, Buttercup, Hyacinth, Freesia, Rain Lilly, Tuberosa and Watsonia.
Prior to division, thoroughly water the plants to be separated. Moistening the soil a day or two in advance will make digging and separation much easier. Watering will also help to ‘plump up’ plants and make them less prone to moisture loss through the transplanting process.
In dividing the clump, use a sharp garden shovel do dig around and under the clump. Dig a few inches beyond the plant and down 10 to 12 inches deep. After you have undercut the plant, lift it out of the soil and place it on plastic sheeting or newspaper. Begin separating the individual plants with your fingers. If it’s too difficult to pry apart the clump, use a spade or garden fork to separate individual plants. In the process you’ll be cutting through and dividing roots as well.
After separating the clump, discard any weak or damaged plants. If the Mother plant in the center of the clump is weak or dying, discard it as well. Only replant healthy, vigorous individuals.
The bed or spot where divided perennials are to be located should be amended with organic matter. Mix generous amounts of bagged compost, peat, bagged topsoil, potting soil or manure into the top 12 inches of soil. To stimulate new root development on your divided perennials, mix in 2 pounds of ammonium phosphate (16-20-0) or other high phosphorous fertilizer for every 100 square feet of bed area. For smaller spots or for planting individual plants, mix in 2 tablespoons for every square foot of planting area.
It’s important to space plants far enough apart to give them room to grow without crowding. Also, set plants at the same depth in the soil that they were growing originally. Do not cover the crowns of plants with soil as this will cause the stems to rot.
Finally, cover the soil surface around your newly transplanted perennials with bagged forest mulch, chipped bark, shredded wood mulch, or course compost to help hold in moisture. Water often enough through the fall to keep the soil moist, but not wet.
“Trees for Tucson” will be the topic for this week’s garden demonstrations. They will be presented on Wednesday at 9 a.m. at the Pima County Extension Center, 4210 N. Campbell Ave (central); and at 1 p.m. at the Wilmot Library (east). Due to the Veteran’s Day Holiday there will no program presented at the Oro Valley Public Library.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
- Updated: November 6, 2005
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