Planting Bearded Irises

Learn The Tricks To Success

From Your Friends At Schriemer's

Irises are among the most cherished of perennials, providing not only delicate blooms in June in a rainbow of colours, but fan-like sprays of foliage that remain attractive in the garden all summer long. Bearded irises are the most popular type, with their large standards and falls in various contrasting colours. There are literally thousands of named varieties ranging in height from tiny to enormous, all of them breathtaking. While irises are easy to grow in Manitoba, the secret to success is in the planting. Follow these instructions and you should have healthy irises in your garden for years to come.

Note that this discussion applies only to the bearded type of irises, which have unique cultural requirements. There are numerous other species of iris (for example Siberian, crested and Japanese iris, to name a few), and all have different cultural requirements, so be sure you know what type you are planting.

Planting Location

The biggest problem with bearded irises is root rot. This occurs when they are planted in a wet or poorly drained location in the garden, when they are over-watered or over-fertilized, or if they are planted too deeply. Luckily, this is an easy problem to avoid at planting time.

The planting location is key. Bearded irises need full sun, so plant them where they will receive at least 6-8 hours of direct sunlight each day. They will grow in most garden soils, but the soil must be perfectly drained. Avoid planting them in low spots or locations in the garden that accumulate water in spring or after a rainfall. Raised beds or berm gardens are ideal, as are dry locations against the house.

Planting Instructions

Rhizomes are the tuberous underground "bulbs" from which the foliage and flowers emerge in spring. They are not bulbs in the true sense, but rather large fleshy storage vessels that slowly spread under the ground, forming attractive clumps of irises which can later be divided. Much like you would grow potatoes in your vegetable garden, bearded irises can be grown from a single healthy rhizome. This is often how irises are sold, and it is a very effective and relatively inexpensive way to bring irises into your garden.

Rhizomes can be planted either in spring or in late summer. Most commercial varieties are offered in late summer because spring-planted rhizomes are not likely to flower until the following year. A healthy rhizome is intact and has a "fan" of foliage and a root node. It's not a concern if the rhizome is dry on the outside; in fact, it should be quite dry. If it's a little damp, you can let the rhizome dry out for a few days before planting. It is not necessary to soak the rhizome before planting.

To plant a bearded iris rhizome, your objective must be to keep the rhizome at or slightly above the soil level, with the fan facing upwards and the roots extending downwards into the soil. In light or sandy soils, set the rhizome half a centimetre below the soil, while in heavy clay soils, the top of the rhizome should be slightly exposed. The easiest way to plant an iris rhizome is to dig a hole in the garden and then form a mound of soil with the peak just below the soil level and two short trenches on either side extending about 3-4" deep. Place the rhizome on top of the mound, and guide the roots down into the trenches on either side. Backfill the trenches and mound so that the rhizome is almost completely covered, and the fan is protruding above the soil level. Do not cover the crown with mulch. Water well, then just leave it alone!

If your bearded iris is growing in a pot, you should be able to see a little of the rhizome at the base of the plant. Dig a hole in the garden the same diameter and depth as the root mass, and carefully plant the iris with its crown at soil level. Never plant deeper than its original soil level, or you'll be inviting root rot down the road!

Care After Planting

Irises are very easy to grow once they've been properly planted. They prefer average to dry garden conditions, so be careful not to over-water them. They are not heavy feeders, so regular fertilization is usually unnecessary. After blooming in June, bearded irises go through a natural period of dormancy in mid-summer. It is very important that they be kept particularly dry over this period. They will resume growth in late summer in preparation for the coming season.

Because they spread to form large clumps and the centres tend to thin out, bearded irises should be divided every 3-5 years. The ideal time to divide them is in late July or early August, about 4 weeks after they have flowered. Dig them up, and separate the clumps into individual rhizomes which contain at least one healthy fan and a set of roots. The outer rhizomes tend to be healthier and more vigorous, so discard the older parts from the centre of the plant. Allow the rhizomes to dry out for a couple of days before replanting, then follow the instructions above.