World Photo by Jolene Guzman

If you’ve been bitten by the iris-viris (a very serious affliction!) here are some suggestions for success.

Growing conditions

• Lots of Sun: Bearded Iris like lots of sun, at least 4-5 hours daily.

• Well-drained soil: Bearded irises, the most common garden variety, need well-drained soil and will rot if allowed to stand in water. Plant rhizomes just below the surface in sandy soil or even with the surface in clay soil. Irises are drought-tolerant and like sun directly on the rhizomes to keep them dry.

• Clay soil amendments: Add gypsum (bearded iris like the calcium) at the rate of one pound per square foot, peat moss at the rate of one cubic foot for every 25 square feet of garden space and alfalfa pellets at the rate of one pound per square foot. Cover with a two-inch layer of compost and dig or rototill the added ingredients into the soil until well-blended and loose soil results.

• Neutral to slightly alkaline:  Bearded iris like neutral to slightly alkaline soil. Because the heavy winter rain on Oregon’s South Coast can create acid soil, add lime to increase alkalinity. Siberian and Japanese irises like a neutral to slightly acid soil.

To plant or divide

The ideal time to divide irises is one month after bloom and the best months to plant irises are July through September.

• Distance Apart:  Plant rhizomes one to two feet apart, as each rhizome will become a large clump in two or three years. When planting a rhizome, place the “toe” to the front of the garden. Three rhizomes placed in a triangle with the “toes” facing (even touching) the center make very nice landscaping clumps.

• Dividing Clumps:  Divide clumps every three to five years. Cut and replant newer rhizomes from the “mother rhizome.” Discard the “mother rhizome” because older rhizomes become woody and are more susceptible to rot and disease.

Bugs and bads

• Root Rot:  Root rot may be caused by excessive water conditions, poor drainage or an acidic soil. Remove the soft, rotten portion, dust “cuts” with powdered bleach, and expose to the air and/or sun to dry the rhizome before replanting.

• Iris Borer: Eggs winter over on lower parts of stalks, leaves, or debris near the ground, or in the cracks of rhizomes. Good fall and/or spring clean up and disposal of debris will eliminate many eggs. Never compost iris leaves.

The larva is pinkish-white with a brownish-red head. The best time to get the borer is when it’s still on the leaf. Spraying foliage and plant with Bayer’s Advanced Lawn Season-Long Grub Control in the early spring. The key ingredient is “Merit.”

When newly tunneled borer holes are found in the rhizomes, but no larvae, search the soil for pupae, which look like brown nuts in the soil. Treat for those if they are there.

• Leaf Spot: Although unsightly, leaf spot usually will not kill the plant, but may affect growth. It can occur in wet spring weather, but generally stops during warm, dry weather.