·Study the plant you wish to divide. Is it a good candidate for root division?Does it grow from the outside of its root clump? Does it make new bulbs? Does it make suckers?
·Figure out where you want to put the divisions and prepare ground, have pots and soil ready.
·Use shovel to dig around the plant to be removed. Use spading forks to lift and separate the clumps. With offshoots use clippers to cut umbilical root.Cut 1/3 tops off. For roots to be separated, wash off dirt enough to see where the eyes, plantlets are so each new division has new growth.
·Keep moist and plant soon in new location. Fertilize every other week until mid-summer then stop to let plant harden off for winter. Keep well weeded and mulched.
·For most plants late winter early spring is the optimum time to divide.For bulbs, primrose, iris, divide after bloom.For peonies fall is best.
·You can divide horse radish, rhubarb and French terragon
·Plants not easily divided: needled and non-needled evergreens (azalea, Rhodies, holly, laurel), many trees,blueberry,annuals, some perennials with single tap roots.
Secrets of Plant Propagation by Lewis Hill(a paperback)