How to Grow Bearded Iris
Once the spring bulbs finish blooming, there is often a time gap before the herbaceous perennials begin to bloom. Bearded iris (Iris germanica) fill in this gap splendidly, blooming in April through mid-June, depending on the variety. The shorter bearded iris, such as the dwarf varieties bloom earlier while the elegant tall bearded iris bloom later in May to mid-June. No matter which type you grow, you can depend on them to bloom for a full two weeks.
Iris are named after the Greek goddess of the rainbow because they come in every color except true red. Breeders have been trying to hybridize red iris since the Middle Ages. Iris are most commonly seen in shades of purple, but they can also be pink, yellow, white and blue. So-called “black iris” are actually very dark purples.
Iris are native to the northern hemisphere and are commonly found in dry, semi-arid or rocky mountainous areas. You should keep that in mind when planning your garden. You should plant your iris in well-drained soil. If too wet, iris will rot so it is not a good idea to plant them in areas that tend to be wet. The exception to this are the yellow flag iris which like to grow in moist areas and are often used in water purification ponds to control agricultural run-off.
Bearded iris come in every size from the tiny eight inch dwarf iris to the 48 inch tall iris. The smaller varieties grow from bulbs which should be planted about one inch deep in the ground. Like most spring blooming bulbs, they are planted in the fall before the ground freezes. The foliage is grass-like and emerges in the spring. At the end of the season, it dies back and should be removed from the garden. Leaving it in your garden over the winter invites pests to over winter in it.
The taller iris grow from rhizomes which sit on top of the ground and should not be covered. The roots, which grow from the bottom of the rhizomes, do grow into the soil. Iris should be planted in the summer and early fall. They need time for the roots to become established so the latest that they should be planted is at least six weeks before your first frost. If the roots heave out of the ground during the winter, don’t try to force them back down. Instead, lightly cover them with soil to protect them from the cold.
All iris like full sun, at least a minimum of 6 hours of sunlight each day. You can fertilize by lightly digging compost in around your plants or using 6-10-10 fertilizer in the spring when the iris start growing and again about a month after they finish blooming to boost food production in the bulbs or rhizomes.
After they finish blooming, you should cut the flower stems down to the ground. Allowing them to go to seed robs the plant of energy that should be directed to the bulb or rhizome to help it survive the winter. Removing the spent flowers immediately is especially necessary if you are growing re-blooming iris. They will not rebloom if you allow the first flush of flowers to mature to seeds. If you remove the first flowers on your reblooming iris, you can expect a second flush of flowers in 4 to 8 weeks. Reblooming is not guaranteed, however.
Plant the rhizomes 12 to 24 inches apart so that they do not become crowded too quickly. Crowding encourages pests and disease and fewer flowers. Divide your clumps every 3 to 4 years. Using a garden fork, carefully dig up the clumps of rhizomes. Break them apart. Replant the outer young rhizomes and discard the center old ones. Division should be done about a month after your iris finishes blooming. Newly planted iris and newly divided iris should be watered regularly until fall so that they become established. In the fall, cut down the foliage to 4” to 5”. The fans of new foliage will emerge in the spring after your last frost.
Iris can be grown in containers. Use a 6” to 8” pot for dwarf iris and a larger 12” pot for taller iris. Use sterile potting soil, not soil from your garden. Fill the container to within 1” of the rim of the pot to allow you to water. Plant the bulbs of the dwarf iris as you would in the garden. Place the rhizome of the taller iris on the surface of the soil as you would in the garden. Make sure your container gets at least 6 hours of sunlight daily and water it only when it becomes dry. Over-watering will cause the iris to rot, just as in your garden. Divide your plants annually so that they don’t become over-crowded in their containers. You can leave the container outdoors during the winter.
Iris make excellent cut flowers. Harvest your flowers early in the day. Choose buds that are just beginning to open rather than flowers that are fully open. The buds will open in a few hours in the vase. Place your flowers in a bucket of tepid water until you are ready to create your arrangement. When you are ready to arrange them, re-cut the stems about an inch above the original cut at an angle. To ensure the longest life for your flowers, keep your arrangement out of direct sunlight. It’s also a good idea to place it away from drafty doors and windows. Be sure to remove dead and dying flowers promptly.
Bearded iris are easy to grow, come in almost every color imaginable and prolong the spring bloom period in your garden. Even after they have finished blooming, their tall fans of sword like foliage continue to provide architecture to your garden throughout the growing season.
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© 2015 Caren White