Part One Bearded Irises

The bearded iris gains its name from the line ofthick hairs that emerges from the throat of the flower. These hairs form a long, furry caterpillar towards the back of the falls, and their purpose is to guide insects, such as bees, towards the pollen. Bearded irises are the largest group with the greatest number of cultivated varieties. They are also the most popular group of irises for garden use.

In the wild, bearded irises grow in an area that stretches from the Mediterranean to Southeast Asia and from the Arabian Peninsula north to southern Russia. They usually are found in a sunny place where the soil is poor and well drained. The flowers, which always have large petals, are borne on stiff stems above broad, sword-like, and usually soft green leaves. These form a handsome clump that is invaluable in a garden.

The bearded group is divided into two smaller groups: the pogon irises and aril irises. Pogon irises are the bearded irises we all know and love. They are cultivated throughout Europe, in North America in states that are north of Florida, and in Australia and New Zealand. The arils, which have both beards and rhizomes, are distinguished by the white appendage that is attached to the seed. These are very exotic, but difficult to grow in the countries where pogon irises grow as they need almost desert conditions to thrive. Arils include the Oncocyclus, Regelia, and Pseudoregelia irises. This latter group is not included in this book as so few plants are available to gardeners; however, the beauty of the flowers has been so admired by hybridizers that crosses between these and pogon irises have produced plants called arilbreds.

The information given here is for bearded or pogon irises of garden origin.

Horticultural Classification of Bearded Irises

By the 1950s the number of bearded cultivars was so large and varied that the American Iris Society decided to separate the hybrids into different categories, using both height and flowering time. This classification has changed slightly over the years and is now recognized throughout the world. Although the system was created by iris breeders, it has become a useful tool for gardeners to help choose the right iris for the right spot and to select plants that will extend the flowering period in the garden.

Miniature Dwarf Bearded (MDB): These grow up to 20 cm (8 in.) tall and bloom during midspring. They are the first bearded irises to flower and form low, spreading clumps with a mass of small blooms. They are useful for growing in rockeries and alpine gardens.

Standard Dwarf Bearded (SDB): These grow 20-38 cm (8-15 in.) tall and bloom in midspring after the MDB irises. The flowers are borne just above a broad clump of leaves. These irises are ideal for growing at the front of a border.

Iris 'Apricot Drops', a Miniature Tall Bearded iris

Intermediate Bearded (IB): These grow 38-71 cm (15-28— in.) tall and bloom after SDB irises. The flowers are borne above the foliage. These irises are vigorous enough to grow in a border with other perennials.

Border Bearded (BB): These grow 38-71 cm (15-28— in.) tall and bloom after the IB irises at the same time as the MTB and TB irises. They are smaller forms ofTB irises, but like IB irises are vigorous enough grow in a mixed border.

Miniature Tall Bearded (MTB): These grow 38-71 cm (15-28— in.) tall and bloom at the same time as BB and TB irises. They produce delicate flowers and flower stems but do not grow as vigorously as the BB and TB irises. When grown in a border they should not be allowed to be swamped by other plants.

Tall Bearded (TB): These grow more than 71 cm (28— in.) tall and are the largest, most glamorous bearded irises and the last group to bloom. They can be grown in a flowerbed of their own, as a focal point, or combined with other plants; however, they must be given space so the rhizomes get enough sun to create flowers for the following season.

Cultivation and Maintenance

Although bearded irises are easy to grow, they do need to be grown correctly. The rhizomes need to be baked by the sun to produce flowers the following flowering season. When planting bearded irises, make sure they are spaced so that neighbouring plants will not encroach on them.

Many of the older Tall Bearded cultivars thrive with partial shade and, in climates where the summers are very hot, a partially shady site can be advantageous. The soil in all situations must be well drained. If it is wet, the rhizome will rot. In heavier soils, dig in sand, grit, or well-rotted compost before planting to allow the soil to drain. In very wet soils, particularly those that are wet during the winter or those that contain a lot of clay, plant bearded irises on a well-drained slope or in a raised bed. The soil needs to be balanced and not too

Non Bearded Iris

Iris Az Ap', an Intermediate Bearded iris Iris 'Blackbeard', a Border Bearded iris

Standard Dwarf Bearded Iris Garden
Iris 'Coral Carpet', a Miniature Dwarf Bearded iris Iris pallida, a Tall Bearded iris

rich. Bearded irises can cope with a small amount of acidity, but a very acid soil will cause the rhizomes to rot.


Generally Tall Bearded irises should be spaced at least 30 cm (12— in.) apart. Smaller varieties can be placed as close as 23 cm (9 in.) apart. For the best effect, plant Tall Bearded irises in groups of odd numbers, preferably in threes. If they are being planted in a border with other perennials, place them in a triangle or circle with the nonfoliage ends of the rhizomes pointing inwards, towards each other. This gives the plants an open central area so the sun can get to the rhizomes and provide a barrier to prevent other plants from creeping over and between them.


The best time to plant bearded irises is just before the new roots start to grow. Traditionally this is about six weeks after flowering; however, I feel it is much better to divide and replant bearded irises in early autumn or after the hottest and driest part of the summer. At this time the rhizomes are fully mature, they have become dormant, and the ground is damper and still warm. Bearded irises can also be planted in spring, although doing so means they are unlikely to flower the same summer.


When planting a bearded iris, first trim the foliage back to the length of a hand and, again this is traditional, into a pointed V shape. This stops the plant from popping out of the ground in windy conditions and reduces water loss after planting. Also trim back the old, long roots. As these roots die back after the plant flowers, they are simply there to anchor the rhizome into the ground until the new roots grow. Trimming old roots not only makes it easier to plant the rhizome, but also stops birds, such as rooks, from pulling at stray roots that resemble worms and uprooting the plants.


Many books will tell you to dig a shallow hole, leave a small hump in the middle of the hole, put the rhizome on this with the roots spread out to each side, back fill the hole, and firm the soil well. I see no reason to do this. At our nursery we plant bearded irises by machine. The machine makes a furrow, drops the iris in, then pushes soil back over the plant. Therefore a simpler method of planting bearded irises is to dig a hole deep enough to accommodate the root, put the roots in the hole making sure to leave no gap under the base of the rhizome, and then back fill the hole with soil.


The depth a rhizome is planted is important. Summers in Britain are not as sunny as those of hotter regions; therefore, English gardeners need to plant the rhizome at soil level so that it gets the maximum amount of sun. In other areas where the summers are hot and sunny, the rhizome should be planted up to 2.5 cm (1 in.) below soil level. Finally, in gardens that are frequently irrigated or in areas with high rainfall, the rhizome should be planted high up, on a mound of soil, so that water will not sit around the rhizome. If planted a little too deeply, a rhizome tends to push itself back up to the surface, that is, if it does not rot first.


In areas with high rainfall it is not necessary to water the rhizome after planting. If no rainfall is expected, watering will stimulate new root growth and be beneficial to the plant. In my experience, only a third to a half of all bearded irises will produce flowers the following year, but all should flower by their second season. If they do not, make sure the irises are in full sun, get water during the time they produce the flower stems, are not planted too deeply, and face no competition from surrounding plants.


Because irises are vigorous plants, it is beneficial, though not critical, to fertilize them twice a year, particularly if they are growing in a poor soil or have been in the same spot for more than a year. Do this once in spring when plants are putting on new leaf growth, as it will help the production of strong flower spikes and foliage, and again after plants have bloomed, when new roots are being produced. A granular slow-release fer-

tilizer low in nitrogen is ideal. Fertilizers made from seaweed are also okay, as is a dressing of four parts bone meal, two parts superphosphate of lime, and one part each of sulphate of ammonia and sulphate of potash. Mix these ingredients thoroughly and apply at a rate of 60 to 75 g per square meter (2-2— oz. per square yard). Over fertilization will produce soft growth, which can lead to rhizome rot. Too much nitrogen, too much water, or an acid soil will have the same effect on iris rhizomes.


Bearded irises need to be lifted and divided at least every three years. Failure to do so will lead to fewer flowers. Some varieties, particularly smaller ones like the Miniature Dwarf Bearded irises and the more vigorous Standard Dwarf Bearded irises, should be divided every two years. To do this, ease the old clump out of the ground with a fork. Shake off the soil and snap the new rhizomes from the old central rhizome, discarding the old rhizome. Tall Bearded irises can be left out of the ground for up to a month; however, rhizomes of smaller types may not last that long and should be planted soon after lifting.


To prevent disease it is important to keep bearded irises tidy. Remove dead, dying, and diseased leaves frequently, and snap off spent flowers stems at the base. It is not necessary to cut the foliage back in the autumn, but old leaves do harbour fungal spores, slugs, and snails during the winter.


Bearded irises are very tough, particularly the older hybrids. In mild and temperate areas they do not need winter protection. Elsewhere severe frosts can uproot the rhizomes, therefore bearded irises should be protected by piling the soil up around the rhizome or by covering it with layers of straw and leaves. Be sure to remove this covering in spring.

Dead Iris Rhizome
New rhizomes attached to old rhizomes
Old Tall Bearded Iris
Untidy leaves

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