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ASK MARTHA: Multiply Your Garden with Division
Martha’s Easy Guide to Dividing Perennials
Question: Hi Martha, do I need to divide my perennials? Can you share your tips?
Martha: I make it a regular part of my gardening to divide well-grown perennials. Division provides a quick, straightforward way to increase your stock of multi-stemmed perennial flowers, ornamental grasses, and bulbs. This form of propagation offers instant gratification: In a matter of minutes, one plant becomes two or even more, depending on the size of the original. Besides multiplying your plants, this procedure typically renews their vigor.
As a plant exhausts the soil around its roots, its crowded tangle of stems bears fewer and fewer blossoms; by transplanting the fragments to fresh soil with room to spread, you return them to vigorous growth and healthy bloom.
Dividing herbaceous perennials every three to five years will keep rapidly spreading plants under control and rejuvenate older plants. It's best to divide fall bloomers and ornamental grasses in spring. Divide spring and summer blooming perennials in fall. (Some tough perennials, such as hostas and daylilies, can be divided anytime.)
How to Divide a Perennial
To reduce moisture loss in the process of dividing, make sure your plants are watered thoroughly before starting. It’s best to water close to the soil surface (see article), to keep roots and soil together.
Choose a cool and cloudy day for working. Prune any fragile stems and foliage down to 6-inches from the ground.
1. Using a sharp pointed trowel, shovel or spading fork, dig deep on all 4 sides of the plant. 4 to 6 inches away from its base. Pry underneath with the tool, and gently lift out the entire clump. Dig around the entire root mass, about ¼- inch beyond the plant's outermost foliage. Go deep to avoid damaging the roots. Carefully lift the plant out onto a tarp laid near the bed.
2. Shake or hose off loose soil and remove any dead leaves and stems. Check the root-ball to see if there are any sections that naturally split off. Some perennials (such as hostas and heleniums) have clumping roots that are easy to separate with your hands. Others (including asters, grasses and daylilies) can be such a tangled mass that you'll need to pry them apart using two garden forks back-to-back, as pictured above. Dahlias and other plants with fleshy, tuberous roots will need to be sliced into sections with a sharp knife. If any roots refuse to snap or break neatly, don't tear them; instead, cut with pruning shears. Torn or frayed tissue heals slowly and offers an entry point for soil-borne pathogens.
3. Check that every new division has a piece of the original stem and a growth bud attached. Discard old, woody roots from the middle of the original clump.
4. For perennials with tough, massive roots or rhizomes, such as this astilbe, use a Japanese weeding knife (Hori Hori) or other sturdy blade to divide the plant in two. Try to cut cleanly, in a single smooth motion.
5. Because tough, dense roots are quite vigorous, you can divide the halves again, to yield four substantial chunks. It's best to plant these divisions as soon as they're made. If you must wait, wrap them in damp newspapers, place them in a plastic bag, seal it, and refrigerate it for no longer than 2 days.
6. Replant as soon as possible (keep roots moist until you do) in new containers or beds, making sure to set the divisions at the same depth as they were in the original bed. Use a good nutrient-rich soil such as 5 out of 5 Customer Rating Miracle-Gro® Garden Soil All-Purpose. Water them well and continue to water once a week for the first few months unless it's particularly rainy. Fertilize after 3 months with Miracle-Gro® Shake 'n Feed Rose & Bloom Plant Food.
Article by Martha Stewart, as part of the Growing with Martha Stewart partnership.