Answer: Iris is a rather undemanding plant, but there are a few basics you should provide to ensure healthy, happy plants. Cut the flowering stems down as soon as the flowers fade, but allow the foliage to remain until it withers down in the fall.
Divide iris beds when the rhizomes become crowded (usually every 3-4 years). This provides a good opportunity to amend the soil with organic matter, which will help it retain just the right amount of moisture for your plants. Late summer is usually the best time to dig and divide iris. Dig up the clumps with a garden spade and separate the rhizomes. Then break away the ends of the rhizome and replant them, discarding the old center of the rhizome. Before replanting you can cut the fan of foliage down to 4" or more (for ease in handling). Dig a shallow trench and lay each rhizome in the trench, spaced about 6" apart, with the ends pointing in the direction you want new growth. Cover with an inch or two of soil and water the bed well. Next spring your renovated iris bed should bloom with great enthusiasm!
A really good basic gardening book is "Gardening for Dummies", IDG Books, 1996, ISBN# 1-56884-644-4.
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