Iris: Bearded Iris
Hardy in Zones 3-9
WHEN TO PLANT OR DIVIDE:
For best results, Bearded Irises should be planted or divided in August to early October, 4 to 6 weeks after blooming. The milder your climate, the later you can plant into the fall. It is important that the roots of newly planted Irises be well established before winter. It helps to soak rhizomes in water for 30 minutes before planting.
WHERE TO PLANT:
Irises need at least a half-day of sun in order to bloom. In cooler areas a whole day is best. The most spectacular bloom occurs in full sun. Be sure to provide your Irises with good drainage by planting on a slope or in raised beds. If a Bearded Iris rhizome sits in water for more than a couple of days, it may rot. Many Bearded Irises are lost in the spring when there is water standing on the ground.
Irises will thrive in most well drained soils. The soil should be worked to a depth of ten inches. If your soil is heavy, organic matter can be added to help drainage. The ideal pH is 6.8 (slightly acid), but bearded irises are tolerant in this regard.
DEPTH TO PLANT:
Bearded Irises should be planted so the tops of the rhizomes are exposed to feel the warmth of the sun while the roots are placed deeper in the soil. Mound the soil in the bottom of the hole and place the rhizome on the mound with the roots flowing unbent over the sides spread out, facing down, where they will enjoy the damp (not soggy) soil. Firm the soil around each rhizome and then water to help settle the soil. A common mistake is to plant Bearded Irises too deeply.
Fertilizer should be applied as a side dressing in early spring. Fertilizer can burn rhizomes, and should be applied around the plant, not on it. Too much nitrogen promotes soft, lush growth that is susceptible to rot, so a 5-10-5/5-10-10 or similar formula is best. You can also work compost into the soil around your Iris.
Distance apart varies according to the effect desired. Close (8-10 inches) for immediate effect. If the plants are 2 feet apart, they will need dividing every 3-4 years, more often if they are closer. If you have more than one rhizome of a cultivar, arrange them in a clump with the leaf end facing out.
When dividing, dig the plant up (a garden fork is the best tool), each division should have one or more sections approximately 2-6 inches with leaves and healthy white roots. Remove and discard the old center rhizomes plus anything that may have rotted or been attacked by pests.
CARE OF PLANTS:
Keep weeds out of the rhizome clumps. Cultivate shallow, since the feeder roots are near the surface. Newly set plants should be kept moist, but established plants rarely need watering. During prolonged dry spells, deep, infrequent watering is best. Aphids, caterpillars, or slugs may damage the flowers or leaves, but rarely do serious harm to the plants. In some years, leaf spot, caused by fungi can make the leaves look unsightly. Cutting off the spotted leaves will improve the appearance of the garden and retard the spread of the disease. Bearded irises may be sprayed with a fungicide. Spray every 10 days to two weeks during the growth period. Old bloom stalks should be broken off at ground level but healthy, green foliage should NOT be cut off. The foliage should be left on the rhizomes, to foster development of new sprouts for next season.
Mulching of bearded irises is to be avoided during the growing season. If you desire to mulch the bed for appearance, you should NOT cover the rhizomes. The sun must reach them to facilitate development of next year's increase. Freezing weather will not harm the rhizomes, other than causing them to heave out of the ground as a result of successive freezes and thaws. A good remedy for this is to mulch with pine needles, sea grass or evergreen boughs after the ground has been frozen. This provides an insulating effect that prevents the ground from thawing and freezing so much as the weather cycles from cold to warm and back again. In the early spring, usually late March, the mulch must be removed. If any roots have been heaved out of the ground, simply cover them with additional soil. We strongly recommend winter mulching new planted Irises! The reason for using pine needles or sea grass is that they do not hold water or get soggy. Prolonged wetness on bearded iris rhizomes may produce rot. Remember to remove mulch in very early spring.