Answer: The best time to do this is in late summer or early fall. If you wish to make a number of divisions, carefully dig up the entire root ball (a heavy digging fork can be helpful) and then divide it into sections, each with at least three "eyes" or growing tips. Larger divsions will make larger plants sooner. Replant them into well prepared soil being careful not to plant them too deeply, about two inches deep is plenty. (Remember that loose soil below the roots will settle a bit over time so settle it without compacting it too much prior to planting as best you can.) Water them in well and mulch around but not over them. Plan on having no blooms for the first few years while they reestablish themselves.
Another method if you wish to leave the parent plant in place is to simply dig out a portion of the plant by digging straight down with a sharp flat spade. Water the mother plant the day before so the soil is moist and the plant is well hydrated, take the piece, then fill in the resulting hole with good soil or compost. Plant the division as above.
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