Answer: It sounds like your iris definitely need dividing. One of the signs to look for when assessing when you need to divide is reduced bloom. Iris are best divided just after blooming has completed, when the plant enters a brief dormancy. It can also be done in early spring but this may delay flowering until the following year. As a rule of thumb, divide plants every 3rd or 4th year for rejuvenation. Division is simple, I simply dig out the clump with a garden fork and pull/cut apart the rhizomes...you'll be surprised how many divisions you get! Another thing I like to do when dividing is dip the rhizomes in a 10 parts water to 1 part bleach solution. This helps keep root rot and root maggots down. Also, when replanting try and keep the very tops visible, this also helps prevent these problems.
Q&A Library Searching Tips