MORE PLANTS BY DIVISION
This is an excellent and fairly easy way to propagate many spreading perennials and grasses, once they have established ‘colonies’ within the garden. Plants that increase by tubers, corms, bulbs, rhizomes or runners can also be propagated by division.
Division will also reinvigorate an established plant colony, and helps avoid congested conditions that can promote diseases such as powdery mildew. Dividing a colony of plants also provides an excellent opportunity to amend and enhance soil conditions; which will enhance new growth and flowering within the ‘mother plant’colony.
Perennial plants that create colonies by a spreading rootstock, such as asters or yarrow, are easily increased by division. Rough division can be done by using a narrow transplant spade to cut right into the established growth and remove a clump of plants, which can then simply be replanted in the garden.
Finer practices include digging up a large section of the plant and breaking it apart with your hands, pruning shears or a knife. Some clumps can be easily pulled apart, but others will need to be cut or pried apart. A hori knife or a hand fork are excellent tools to use to pry clumps apart; two, used back to back and levered against each other are even better! A spray of water can also be used to remove excess soil and expose the roots and crowns.
Examine the freshly dug clump to clearly see the crowns and any new buds and shoots, and to determine where to separate the clump. Fine root hairs die very quickly when exposed to sunlight, so be sure you are working in the shade, and have a container of moist soil on hand to protect the roots of your new plantlets while you prepare all the divisions for replanting.
If you’re planning to pot up your divisions, carefully break the clumps down to a size that will fit into the container you are using. Trim off any damaged or over-sized roots, as well as much of the old foliage or large leaves, but retain all the new growth evident. Always keep more roots than shoots! When dividing bunchgrasses cut down the top growth by half, and cut off the bottommost roots by about a quarter.
Keep your newly potted divisions evenly moist and in a shady spot; gradually moving them into the exposure required by the species. Use a mild liquid fertilizer, and continue to pot up into larger containers as growth demands.
The best time to divide plants is during the rainy season; usually anytime between October to March. Spring and summer bloomers are best divided in the fall, if possible; late summer or fall bloomers are best divided in early spring. Plants are good candidates for division when the herbaceous growth has mostly died back, but new shoots and buds are present and protected under this old growth.
Good candidates for fall division include: Hummingbird Sage, Yarrow, Strawberries, Meadow Sedge, Skullcaps, Yerba Buena, Showy Milkweed, and Pacific Coast Iris
Good candidates for spring division include: Goldenrod, Asters, California Fuschia, Pearly Everlasting, and some of the Penstemons