What Irises Need

Iris rhizome. (By Deborah Canington -- University Of California At Davis)

Location: Iris rhizomes are planted in a sunny site free from other plant competition. The top of the rhizome should be exposed.

Soil: Free-draining soil is critical for success. Amend garden soil with sand, compost and a little lime. Don't plant in heavy clay or waterlogged soil or in areas with automatic irrigation.

Weeding: Iris beds should be kept weed-free or flowering will diminish or cease. Take care not to damage rhizomes.

Dividing: Clumps become crowded, with reduced blooming, after three or four years. Lift clumps six to eight weeks after flowering and separate. Soak the divisions in a bleach solution to kill pests and diseases before replanting, or share them with other gardeners. Dry the rhizomes for a day to callus wounds.

Mulching: Mulch can be laid between clumps but not atop rhizomes or crowns.

Pests: The most serious pest is the iris borer, which enters the leaf in late April and tunnels to the rhizomes. The problem is localized and you may not have it. The grub causes streaks in the leaves as well as leaf wilting and rhizome "bleeding." Clean up all debris in the fall and treat your bed with a systemic insecticide in March after new growth begins.

Diseases: Rhizome soft rot is common in some varieties and in wet growing seasons. Areas of rot can be scraped out with a spoon with the plant still in the ground. Sprinkle the wound with a household cleaner containing bleach. Leaf spot is prevented with a fungicide spray.

Feeding: Avoid high-nitrogen fertilizers, including wayward lawn fertilizers. Feed with a little bone meal in early spring and again after flowering.

Adrian Higgins