Classroom Iris Program

Bearded Iris Culture

Bearded irises are one of the easiest perennials to grow. With a minimum of care they will produce beautiful blooms year after year.

For best results, plant iris rhizomes in July, August, or September. The roots of newly planted iris must be well established before the end of the growing season. In areas with mild winters and hot summers, irises may be planted in September or October.

Iris require at least a half-day of sun. Some shade is beneficial in extremely hot climates, but in general irises do best in full sun. Provide your irises with good drainage by planting on a slope or in raised beds.

Irises will thrive in most well drained soils. If your soil is heavy, coarse sand and humus may be added to improve drainage. Gypsum is an excellent soil conditioner that can improve most clay soils. The ideal pH for irises is 6.8 (slightly acidic) but irises are quite tolerant of less-than-perfect soils. Have your soil tested before making corrections. Lime may be added to acidic soils and sulfur may be added to alkaline soils.

Irises should be planted so the tops of the rhizomes are visible. Spread roots beneath and tamp soil firmly to anchor the rhizomes until new roots begin to grow. Water well at planting time. In extremely hot climates or with very light soils, cover rhizomes with one inch of soil IT IS A COMMON MISTAKE TO PLANT IRISES TOO DEEPLY.

Planting rhizomes 12 to 24 inches apart is the norm. Close planting results in instant color but makes dividing clumps a necessity in 2 to 3 years.

Newly planted rhizomes need moisture so their root systems develop. Once established, irises usually do not need watering except in arid regions. Deep watering on occasion is better than frequent shallow watering. OVER WATERING OF IRISES IS A COMMON MISTAKE.

Soil type for your area will determine your fertilizer needs. Superphosphate, alfalfa pellet (without salt), bone meal, or 6-10-10 fertilizer are recommended. Avoid anything high in nitrogen as it encourages soft rot. A light application in early spring and again a month after bloom is appreciated. Place fertilizer around rhizomes, not directly on them.

When irises become crowed, usually 3 to 4 years, bloom will decline. At this time, old clumps may be thinned by removing several divisions and leaving a portion of the clump in the ground. A better practice is to remove the entire clump, replenish the soil and replant a few large rhizomes.

It is extremely important to keep your iris beds free of weeds and fallen leaves so the rhizomes may bask in the sun. Space plants so there is good air circulation to help prevent diseases. Break out bloomstalks as soon as bloom season is over. This prevents contamination of your named varieties by chance bee crosses. These crosses would cause seed pods to form that might go unnoticed. If given time to ripen, they might drop seeds resulting in new plants that are often unattractive. So breaking out bloomstalks right away is a good garden practice.

The Bulletin of the American Iris Society lists dozens of commercial growers. Look in the back section of any AIS Bulletin for this information. Also visit the web site at for other iris news. There are links to the AIS Sections (specialty groups), regions and local iris clubs. Most commercial growers have web sites where their irises may be viewed before purchase.