ALL ABOUT IRIS

PLAN FOR SUCCESS

SUN OR SHADE: Iris flower best in full sun, though most can also be grown in dappled shade. 

ZONE: Iris reticulata and Dutch iris are hardy in zones 5-9. Bearded iris, Siberian iris and Japanese iris are winter hardy in zones 3-9. Louisiana iris are hardy in zones 6-9. 

WHEN TO PLANT: Plant iris reticulata in fall for spring flowers. Plant other types of iris in early spring or early fall when the plants are dormant. Potted plants may be planted at any time during the growing season.

TYPES OF IRIS

BEARDED IRIS: Sometimes called German iris, bearded iris flower in mid to late spring. The flowers have cascading petals ("falls") and running down the center of each fall is a “beard” that resembles a furry caterpillar. The foliage of is flattened and sword-like. Depending on the type (dwarf, intermediate, tall), the plants may stand just a few inches tall or more than 2 feet tall. Bearded iris have thick, fleshy roots (rhizomes) that grow on or very close to the soil surface. They should be grown in full sun and prefer neutral to slightly acidic soil that is very well drained.

BEARDLESS IRIS: The plants in this iris family include Siberian iris, Ensata iris (also known as Japanese iris) and Louisiana iris. All have an upright form with long, strappy foliage and dense and fibrous roots. They can be grown in full sun or partial shade.

Siberian iris are extremely hardy, vigorous and adaptable. Their stiff, upright foliage maintains its good looks all season long. Siberian iris flowers are smaller than bearded iris and do not have a beard. They prefer relatively acidic soil and consistent moisture, but will tolerate periods of dry weather.

Japanese iris flowere are as big as an outstretched hand, with an open face and broad, ruffled falls. They need moist soil and are ideal for planting beside a pond or stream.

Louisiana iris flowers can be as subtle as wildflowers or as big and flashy as bearded iris. The plants are not as winter hardy as other types  and perform best in moist soil, where summers are hot and humid.

BULBOUS IRIS:  This iris family includes Dutch iris (Iris x hollandica), Spanish iris (Iris xiphium) and spring-blooming Iris reticulata. All iris that grow from bulbs are planted in the fall and should be grown in full sun. After flowering, their foliage fades away and the bulb stays dormant until the following spring. Like many other spring-blooming bulbs, bulbous iris need to be grown in well drained soil that stays relatively dry during the summer months.

WHERE TO PLANT IRIS

PERENNIAL GARDENS   Bearded iris are classic plants for perennial gardens. They bloom in early summer at the same time as peonies, poppies, lupine and dianthus. Siberian iris are also good performers in a mixed perennial garden. Even when the plants are not in bloom, their upright, grassy foliage adds a strong vertical accent.

NATURALIZED PLANTINGS   Siberian iris are ideal companions for ornamental grasses, sedum, rudbeckia and other naturalistic, low maintenance perennials. The edges of ponds and streams can be beautified with Japanese or Louisiana iris. Both prefer consistently moist soil and will thrive with little or no attention.

ROCK GARDENS AND DRY AREAS   Bearded iris need moisture in the spring, but once they have finished flowering, the plants go dormant and the rhizomes should be kept as warm and dry as possible. Coarse, fast-draining soil is ideal, so consider planting them at the edge of a sidewalk or in a poor, gravely area.

RAIN GARDENS  Siberian iris need moisture to get established, but after a year or two the plants become very drought tolerant. They will tolerate poor soil and alternating periods of wet and dry.

CUTTING GARDENS   All iris are great cut flowers. Though each blossom lasts only a day or two, each stem usually has multiple buds and will provide a week or more of flowers.

HOW TO PLANT IRIS

Loosen the soil 12” and mix in several handfuls of compost and ¼ cup of all-purpose granular fertilizer (follow package directions).

For bearded iris, position the rhizomes horizontally and leave them partially exposed to the sun. For other types, position the crown of the plant (where the roots meet the stem) about 1 ½” below the soil surface. For bulbs, plant 4 to 5” deep, depending on type.

Cover with soil and water as needed.

TIPS FOR GROWING IRIS

Bearded iris should have access to plenty of moisture from spring until they finish flowering. Then from midsummer through fall and winter, the soil should be kept as dry as possible. To minimize fungal diseases, avoid crowding the plants and make sure there is good air circulation around the foliage.

During the first growing season, while the plants are getting established, beardless iris should be watered weekly or when the soil is dry. Like all perennials, it will take a full year for the plants to settle in and begin producing a great display of flowers.

CARING FOR IRIS

Iris begin active growth in very early spring and this is the ideal time to fertilize the plants. Distribute a shovelful of compost around the base of the plant. For bearded iris, make sure not to cover the rhizomes.

Dividing bearded iris every two to three years will ensure you always get good flower production. Divide the plants in mid-summer, about a month after the flowers have faded.

Use scissors to cut the foliage back to one-third its original height. Dig the clumps and separate healthy new rhizomes from older, less-productive rhizomes that will be located toward the center of the clump. Discard any rhizomes with holes (from insect damage, see Iris Borer, below) or soft spots. When dividing large rhizomes, make sure each section has at least one set of 3 to 4 leaves. Replant, leaving 10-12" between rhizomes.

When dividing other types of iris (such as Siberian and Japanese), it's usually easiest to dig out the entire root ball and then divide it with a spade or knife. Replant only the healthiest chunks. Another alternative is to just use a sharp spade to carve out and remove any dead or weak areas.

IRIS BORER

In the eastern US, the iris borer can cause problems for all kinds or iris. Though this pest seldom kills the plant, it causes streaked or spotted leaves and can make the rhizomes mushy. The borer is a pinkish caterpillar that burrows into the leaves and then starts moving down into the root zone. As the caterpillars feed on the rhizomes, the plants are exposed to diseases including bacterial soft rot and leaf spot.

To avoid the iris borer, trim back all foliage in the fall after the first heavy frost. Destroying the foliage will eliminate many of next year’s eggs. When dividing plants, look for signs of iris borer damage and remove any affected parts. If borers are a serious problem in your garden, you'll find Siberian iris are considerably more tolerant than other types of iris.

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