Planting areas: Sunset Zones 1 to 24, USDA Zones 3 to 10
Size: 6 inches to 4 feet high
Bloom season: Late spring and early summer.
Exposure: 6 to 8 hours of sun per day
Pruning needs: None until after bloom
Water needs: Water when soil is dry 2 inches down; water deeply but infrequently.
Snapshot: Irises are perennial plants that grow from bulbs, or, rhizomes.
Of three main categories of iris that grow from rhizomes, bearded iris is the most widely grown. (The other two categories are beardless and crested.)
The flowers are showy, generally with three inner segments and three droopy petals, each with a fuzzy spot, or beard, near its base. Most irises bloom yearly, but some varieties bloom a second time in late summer.
Colors include purple, red, pink, yellow and white, and combinations abound. Leaves are tall, green sword-like fans.
In locations where winters are mild, including parts of San Luis Obispo County, plant bearded iris rhizomes in the fall in well-drained soil in the ground or in containers with a minimum 12-inch diameter and a drainage hole. Loosen soil to 2 to 3 feet so roots can get deep before it rains.
Plant in full sun in cool climates. In the hottest regions, irises will accept light shade during the afternoon.
Place rhizomes just below the soil surface with leafy end up, spreading roots out — spacing rhizomes 1 to 2 feet apart or in clusters 18 to 20 inches apart.
Fertilize with a 10-10-10 or 5-10-10 water-soluble fertilizer when planting and once more after blooming begins. (Don’t let the fertilizer touch the rhizome, or it may burn.) Spray with water or insecticidal soap if aphids or other pests appear on leaves; stop applications when pests are gone.
Once blooming is finished, cut the stalk to the ground and leave the green leaves. This will allow the nutrients to be absorbed into the rhizome to produce next year’s blooms.
Cut the foliage back in late summer or fall when the leaves are entirely yellow.
Rhizomes can be divided every 3 to 5 years to prevent over-crowding. When dividing, dig up the rhizome, cut into 3- to 6-inch pieces with both leaves and white roots. Replant 12 inches apart, just below the surface of the soil.