Bearded Iris

Bearded Iris
Iris germanica
June 2, 2008

Iris is the genus (recall the nomenclature post earlier) of 200 to 300 flowering plants. They are herbaceous perennials that grow from rhizomes or in drier climates bulbs. The have long, erect flowering stems that in our zone bloom from late May to early June. Despite being an herb they are mainly grown as an ornamental plant in the garden. The flowers are quite showy but from my first year experience with them are not long lasting. The flowers can be cut for indoor display. They are fragrant but not as fragrant as other cut flowers. They do look lovely standing to great you as you enter the garden.

I have always wanted Iris but until now did not have them. Now I have two clumps of Bearded Iris, one a white with purple edging and the other a peach. I've never had Iris so it is a learning curve for me. They should be planted in grainy, well drained soil in a sunny location. Avoid over fertilizing as that will cause soft, lush growth that will flop easily. Tall varieties should be avoided in windy areas as they are susceptible to both wind and rain damage. Staking will help prevent wind and rain damage. Iris should be divided every few years when fail to bloom or the number of blooms is reduced. Propagation is by division six to eight weeks after blooming. Simply slice though the clump to form two or more clumps depending on the size of the existing clump leaving a chunk of rhizome and roots for each division. Plant the removed clump into a prepared hole with the fleshy part of the rhizome showing and the roots well covered. If the rhizome is planted too deep the Iris will grow profusely but not flower.

Iris borer (Macronoctura onusta) and thrips are two problems you will encounter when growing Bearded Iris. The Iris borer eggs overwinter on debris or on the crown of the iris. The tiny caterpillar eggs hatch in the spring and bore through the leaf eating their way to the centre of the leaf. By mid-summer the caterpillars are about two inches long and have made their way to the rhizome where they tunnel and eat. As a result the rhizome will become soft, mushy and foul smelling (iris bacterial soft rot). Prevention is the best course of action against the Iris borer. Inspect the plants in the summer looking for dark spots on the leaves. Divide the clump as for propagation, manually remove and kill any Iris borer in the rhizome. Cut away the rot if it is minor or remove the rhizome entirely. Bearded Iris can be dusted with diatomaceous earth in the spring as a preventative measure against Iris borer. During late summer and early fall clean the beds well to eliminate egg laying sites. Remove all debris after the first heavy frost to prevent overwintering eggs. Thrips are tiny white flies that lay their eggs in developing buds. The larva damage the flower surface causing the flowers to become mottled and/or streaked. Some buds may not open or will rot. Control thrips with insecticidal soap or diatomaceous earth as soon as the buds begin forming. Fly tack is an effective controle for adult thrips. Aphids can transmit mosaic virus to Bearded Iris causing the leaves and flowers to become mottled. Affected plants should be destroyed. Control aphids with insecticidal soap.

Happy Gardening!

Garden Gnome
©2007