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Iris Culture In Tucson
Watering: Water immediately after planting, then once a week or so until you see new growth emerging from the top of the fan of leaves. This indicates that the new roots have taken hold. If you water too much before new growth begins, you may invite rot. Better too little than too much water! Irises will not begin to grow vigorously until January. At that time of year, it is time to begin feeding them, and to water more frequently. Water in summer only when summer rains begin to develop! Too much water, combine with heat, can induce rot! Many iris growers do not water at all in summer because the plants are dormant.
Fertilizing: Experienced iris growers choose various feeding methods. Here is one: Begin your feeding program using products such as "Miracle Gro" at one half strength about every two weeks beginning in January until bloom season starts. If plants are slow to take off, feeding intervals can be shortened. The flower stalk develops at the rhizome end where the leaf fan is. New vegetative buds develop on both sides of the rhizome to provide flowers for the next year. That is why we recommend feeding just after bloom season is over with full strength solutions of fertilizer as the new side-shoot rhizomes are actively growing then. Plants are dormant in the summer and no feeding is necessary. Another method starts the same as the above method, and then in February substitute a high phosphorus fertilizer such as "Super Bloom" until after bloom season. At that time switch back to the above method.
Digging and Dividing: When iris clumps become crowded and/or bloom diminishes (3 to 4 years is common), dig from July to September. Dig when the iris beds are dry so rhizomes will not be stored damp. Break apart rhizomes and discard those that are not healthy or have no leaf fans. Remove dried leaves and trim leaf fans to about 6". Trim off excess roots leaving about 4" to anchor rhizome when planting. Using a permanent marker, write the name of the variety on the other center leaf. Wash rhizomes in a 10% solution of bleach water and dry thoroughly. Store as recommended.
Grooming: Keep bed free of weeds, leaf litter, and invasive roots. Cultivate shallowly and not too close to iris clumps. Keep spent blooms picked off to prevent seedpod development. (Unless you are hybridizing) Cut spent flower stalks to the ground. Some TAIS members trim leaf fans back half way after bloom season. This improves air circulation and ease of inspecting conditions of rhizomes.