Imagine all the colours and beauty of a rainbow and you will see the beloved iris. Iris come in many shapes and colours but each one has a graceful elegance that is treasured in the garden. For many iris, the peak blooming time is mid June. Catch them quickly in all their glory before they are gone.
Iris are a large group with the tall bearded types being the best known (and most popular). The "beard" refers to the caterpillar-like hairs on the centre of each lower petal. Many other beardless iris are equally as attractive (including the tall, blue Siberian, flattened Japanese and dwarf bulbous types). Iris can be divided into two sub-groups depending on their underground structures. There are those with fleshy and those with bulbous roots. The fleshy root group includes all iris that grow from fat, creeping underground (or partially exposed) rhizomes such as the bearded, beardless, and crested types. Most iris are deciduous and will die to the ground, leaving a short fan of leaves. Some are even evergreen.
Iris that have fleshy underground storage rhizomes are easy to divide if they become too crowded. Every 4-5 years, dig up the group in late summer when they are dormant and save the healthiest rhizomes for replanting. Cut out and discard any rhizomes with soft sections. This could be signs of soft rot caused by injury from iris borer. Plant suitable rhizomes singly or in groups of 3 with their fans (leafy growing tip) facing outward. This type of iris only grows in one direction (from the end where the leaves emerge). Trim down the fans (leaves) to 15 cm to compensate for the loss of roots. Plant these rhizomes 8-60 cm apart (depending on the plant size). Leave enough room for the iris to grow during the next several years. Do not plant them where they will be shaded by other plants. These iris need full sun. Plant them immediately. Dividing iris can be done from midsummer (for the bearded types) to early fall (for the beardless types). Plant rhizomes for bearded iris so that they are half covered with soil and the rhizome is exposed to sunlight. Beardless iris have rhizomes below the surface of the soil and benefit from a shallow mulching in the spring.
Another (smaller) group of iris contain those that grow from bulbs. This includes the spring blooming reticulata, Juno and xiphium iris. Plant these bulbs early in the fall at a depth of 2 x the diameter of the bulb. Firm the soil and water well. In subsequent years, these same bulbs can be lifted and separated in the early fall if they get too congested.
There are just about as many uses as there are iris types. The taller iris are great for the middle of a border where they tower over shorter perennials (who can hide their often uninteresting foliage). Some hardy, dwarf types can grow in a rock garden or trough. Many moisture-loving iris form clumps of graceful, narrow foliage that are very attractive along a pond or stream edge. These iris are less susceptible to borer and rot problems than those iris growing in dryer soil.
Iris are best planted from midsummer to early autumn because of their growing cycle. Generally they grow in well-drained, moderately fertile soil. Their growth is best in full sun or partial shade. Consider that too much shade and nitrogen fertilizer will reduce the number of blooms and discourage taller iris from standing upright. Too much nitrogen fertilizer and too thick of a mulch layer will also encourage problems with root or rhizome rot. Soil pH is less of a concern than drainage. Iris will grow in neutral, slightly acidic or slightly alkaline soil conditions.
All iris have 6 petals in their flower structure. There are 3 petals called standards that are upright in design. The remaining 3 are called falls and they are downward falling petals. The falls droop away from the centre and alternate with the standards.
A popular type that fits into the beardless rhizome group are the Siberian iris. These iris are highly adaptable in most gardens and quite hardy (zones 4-9). The upright stems and vivid flower colours make them a good choice for a sunny perennial border. Siberian iris are relatively low maintenance plants that can be found in blue, purple, white, yellow, pink, or deep red colours. Their leaves are long, narrow and usually deciduous. This iris should be divided in the fall or early spring while it is still dormant.
The Laevigata iris (also known as water iris) are hardy from zones 3 to 9. They thrive in moist to wet conditions and even tolerate standing water. Their preference is for acidic soils and their blooms can be found in many colours with blue, pink, red, purple, white or yellow being the most popular.
Japanese iris will flourish at the edges of ponds or streams. The large, flattened blooms are very attractive and often reach 25 cm in diameter. The blooms are sometimes double and come in blue, white, purple and pink colours. They are open in early to mid-summer.
The crested group of rhizome iris are called Lophiris or Evansia iris. These plants spread freely by underground stems and produce flat flowers in shades of blue, violet and white. Each flower has a yellow crest or ridge on each fall (instead of the more familiar beard). The flowers and leaves sometimes are found on bamboo-like stems, which vary greatly in height from 5 to 200 cm. A wooded area with good drainage and partial shade is the ideal site for this type of iris.
Most people think of the yellow flag (Iris pseudacorus) as a native plant because it combines so well with the blue flag iris. In actual fact, yellow flag is native to Europe. This extremely vigorous laevigatae iris has upright gray-green leaves to 90 cm long and bright yellow blooms. A close examination will reveal yellow flowers that have brown or violet markings on each fall. This carefree iris is ideal for planting along the banks of large ponds or lakes from zones 5 through 8.
The companion to yellow flag is Iris versicolor, the blue flag. This iris is really native to eastern North America. Each stem has 3-5 violet, purple or lavender-blue flowers that bloom in early summer.
There are two variegated iris that are useful in the garden for vertical accent interest. Iris pallida ‘Variegata’ has bright green leaves with light, golden yellow stripes. Mauve flowers bloom in early June at the same time as the tall bearded iris group. The second variegated type is Iris laevigata ‘Variegata’ which has broad, green and white striped leaves that are 40 cm long. Also blooming in early to midsummer, this iris has pale purple-blue flowers. This laevigatae iris thrives along pond edges and other wet places.
Reprinted on the ICanGarden.com site with permission from Rob Witherspoon at Guelph Turfgrass Institute.