Iris Culture Instructions

To the beginner

Iris is one of the easiest perennials to grow. They survive with less care and reward you with fine bloom with a minimum of attention. These few suggestions are all simple and proper care is very easy.

Soil preparation

Work soil well to a depth of 10 to 12 inches. If soil is heavy, incorporate sand or compost so moisture percolates out quickly. The soil should not be acid. If it is, apply lime, otherwise no lime is recommended. In the preparation of your new iris bed, spade in a good application of compost below the roots. Well-processed compost is ideal. The compost furnishes humus and valuable soil organisms.


Iris will thrive without feeding, but will respond to its application. A nice garden soil will grow fine iris. Use care not to get nitrogenous material on or near the roots, rot may start. An application of a balanced (12-12-12) fertilizer applied as a top dressing dusted around and in between the plants in early spring is desirable. Steamed bone meal and super-phosphate are fine top dressing materials. It is easy to overdo iris fertilizing, but undesirable to omit feeding entirely


Do it shallowly. Iris roots are very near the surface. Keep your iris free of weeds and do not allow neighboring plants to encroach upon them. Remember they should have sunlight right down to the rhizome. Remove the outer leaves as they begin to brown. At all times keep liter, old iris leaves, grasses, etc. away from the rhizomes. Clean cultivation is the finest precaution against iris troubles.

When to plant

For best results plant during July through September. Early planting establishes the new iris plants before winter. This is the time to reset clumps of iris that are crowded, generally clumps 3 to 4 years old. In the extreme heat of the south, it is more advisable to plant after the extremes of summer heat are over. September is recommended.

Depth to plant

Place the rhizomes just below the surface of the ground with the roots well spread out underneath so the rhizome is within reach of the warmth of the sun's rays while the roots beneath are in the moist (not soggy) soil. Be sure to firm the soil tightly around each rhizome when planting. Follow ordinary garden practice of watering and setting soil on newly set plants.


Depends on location. Newly set plants need moisture so they can grow a new root system. They appreciate this attention. Water at fairly long intervals in dry weather. Established plants do not require watering except in very arid parts of the country. The common mistake is to give the iris too much water.

General garden care

We prefer to cultivate shallowly after each rain when the ground has dried sufficiently. As the iris grow, the outside foliage becomes limp. We remove these outside leaves every so often – particularly about two weeks after blooming time. We do not trim the iris foliage on established plants except to cut off some leaf spot should that show up. Bloom stems are cut level with the ground after blooming on a dry day so the cut heals quickly.

Should old clumps be thinned?

Yes, after they become crowded, about every four years. Dig up clumps, remove and discard the old center divisions that have blossomed and replant the fresh, larger foliage fans after the soil has been renovated. If you wish, the old center rhizomes and the smaller fans may be grown in a nursery row for a year and cut into single or double units.

Winter protection

We strongly advocate protective winter covering, particularly in the most northern sections. A light covering of marsh hay, straw or a similar weed-free litter is highly advised. Newly set plants in particular must be protected as a preventative to the injury caused by freezing and thawing. Remove covering when spring growth begins. Late planted irises should have a brick placed on top of rhizome after the first hard freeze to prevent heaving.

Leaf spot

Easily recognized from characteristic brown spots on foliage. Treatment: remove and burn diseased portions; spray or dust with Bordeaux at strength recommended for roses, or a spray of 2 teaspoons of Clorox per quart of water is effective. In case of sprays use a good sticker so spray adheres to foliage.