Growing Iris

Iris is treasured for their early blooming, flowers and low maintenance.  The bold sword shaped foliage is also an excellent backdrop for other perennials and annuals in the garden through the summer.  They’re also an excellent contrast to the more mounded forms of many garden plants.

There are hundreds of species and cultivars of iris which are available in a wide range of brilliant colors.  Iris’ are a versatile perennial and can be used, depending on the variety, as tiny woodland groundcovers or wonderful perennials for the sunny border.  There are also species which thrive in swampy soil.  Iris is a dependable, long-lived perennial species and there is a species for almost any garden situation.

The many different species vary from low groundcovers such as Iris crestata at only 6 inches tall to some of the large Japanese iris at 3 to 4 feet tall. 

Iris prefers full sun for at least 6 hours a day.  In very hot climates, with intense afternoon sun, the flowers of the iris may fade so some late day shade is preferable.

Most iris’ prefer well-drained soil, rich in organic matter.  Japanese and Louisiana iris will grow in wet soil and the yellow flag iris actually prefers to be grown in standing water.  When creating your garden bed, amend the soil with coarse textured organic matter to promote good drainage.  If drainage is a serious problem create raised beds.  Avoid the use of manure when amending the soils as it can encourage iris soft rot. Bearded iris prefers slightly alkaline soil while many beardless iris like a more acidic soil. Test your soil prior to planting.

Fertilize a new iris beds when preparing the garden bed with a complete fertilizer low in nitrogen and high in phosphorus and potassium. Work the fertilizer into the soil and let the bed settle before planting.

Though iris is an easy-care perennial and will survive with little attention, established plants should be fed in the spring and again in the summer after blooming. Reblooming varieties in particular will benefit and are more likely to rebloom with additional fertilizer after their spring bloom.

Deadhead old blooms and stalks after flowering, this will enable the plant to put its energy into growth rather than forming seeds. Removing old blooms and stalks also encourages repeat flowering on reblooming iris.

Bearded iris are grown from a fleshy, bulblike stem called a rhizome that grows horizontally just below the soil surface. Plant iris with the rhizome high in the soil, and the roots well-anchored. Dig two trenches with a ridge between them, place the rhizome on the ridge and spread the roots carefully in the trenches. Then fill the trenches with soil, letting the top surface of the rhizome be just barely beneath the surface of the soil. In heavy clay soils the rhizome should be planted higher so that up to half of the rhizome is exposed above soil level. Firm the soil well and water thoroughly.

After three to five years, iris generally become crowded and should be divided.

There are two basic type of iris, bearded and beardless.  Bearded iris is identified by thick, bushy "beards" on each of the lower petals of the flowers.  Smaller bearded iris generally blooms earlier in the growing season.  Beardless iris has different growing needs than bearded iris. Siberians will tolerate light shade while Japanese and Louisiana iris need full sun.  Louisiana and Japanese also iris prefer moist soil conditions during the hot summer months. All beardless varieties are moderate need to be fertilized regularly and most do best in somewhat acid soil.

Bearded Varieties

Miniature Dwarf Bearded are the smallest bearded iris, with stems reaching only 2 inches to 8 inches tall. They are also the earliest to bloom. They’re ideal for the rock garden and work well when planted at the front of the flowerbed.

Standard Dwarf Bearded iris range in height from 8 inches to 15 inches. They bloom early in the iris season.

Intermediate Bearded iris grow 16 inches to 28 inches and are large enough that their individual stalks may branch, forming an elegant bouquet.
Border Bearded Iris are similar to the intermediate varieties in term or height range and bloom size.  They bloom later, however, with the taller varieties.

Miniature Tall Bearded These iris have blooms that are smaller than on a border bearded on thin and wiry stems. They are well-suited for arrangements.

Beardless Varieties

Siberian Iris are a great, easy to grow, garden perennial with elegant vertical blue-green foliage that looks good throughout the growing season.  The blooms are mostly blue, violet and white. They grow to a height of 2 to 4 feet.  They will tolerate most ordinary garden soil and are among the easiest iris to grow in most regions.

Japanese Iris require a slightly acid soil and have the most spectacular flowers of all the iris.  Blooms are usually huge, ruffled and flat in form.  They bloom about a month after tall bearded iris.  Japanese iris will flourish in wet environments, even in shallow water. These iris require rich organic soil for plenty of nutrients and prefer six hours of full sun.

Dwarf Crested Iris is a small native iris which thrives in lightly shaded gardens.  Light blue flowers in early spring with attractive miniature foliage throughout the summer.  The dwarf crested iris prefers infertile, well-drained soil.

Yellow Flag Iris is a moisture-loving iris which grows 4 to 5 feet tall with yellow flowers. Although it tolerates well-drained areas, it is grows best in standing water, making it ideal for the water garden.

Blue Flag Iris is a beautiful native iris that grows in damp areas in the eastern United States. Lavender-blue flowers on 3-foot stems during May and June.

Dutch Iris are grown from bulbs. Dutch iris bloom in early summer in deep and light blue, purple, yellow and white on 24 inch tall stems. They prefer sun or afternoon shade and organic, well-drained soil. Bulbs should be planted 4 to 6 inches deep in the fall.

Poor flowering is normally due to planting in excessive shade, using too much fertilizer, planting the rhizomes too deep, or, as is the case with most perennials, plants that have become too crowded and need dividing.

Bacterial soft rot is the most serious iris disease. Soft rot causes the rhizomes to become mushy and have a disagreeable odor. Remove any yellowing leaves promptly to help prevent spread of the disease.

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