Now that the last daffodil bloom has faded and tulips are curling up and dropping petals, irises have begun to explode with vibrant showy blossoms.
At a recent meeting of the Fergus Horticultural Society, Kathy Granger, master gardener, spoke about the various iris cultivars, their general care and techniques for removing the dreaded iris borer.
In a presentation, Granger focused on a large collection of personal favourites. Irises are comprised of almost 300 species of showy flowers in a broad range of shades, purple, violet, pink, dark red, blue, orange, bronze, yellow, white and almost black. There is also a wide array of exquisite bi-colours.
The traditional old-fashioned bearded variety (once known as “flags”) is divided based on the height of plants, flower sizes, and flowering season,” instructed Granger.
The bearded variety has been hybridized to form an extensive collection of modern cultivars and sub-groupings.
“For horticultural purposes, many types of irises bloom from early spring to summer, (bearded, beardless, crested, bulbous – Xiphium, Juno and Reticulata)”.
Granger continued that “many varieties thrive in rich, well-drained, slightly alkaline soil in full sun, while others are more tolerant of poorer soil and part sun.”
Irises are perennials. Some varieties grow from creeping tuberous roots called rhizomes and others grow from bulbs.
In horticultural terms, an ornamental bulb is any one of a number of different kinds of underground storage organs which can be dried and from which a plant can grow.
All plants that grow from bulbs or rhizomes store food for the plant and are the reason for the plant’s hardiness and ease of growth,
The rhizomatous species usually have 3–10 spear shaped leaves that grow into dense clumps. The bulbous species have cylindrical leaves.
“They both have long, erect flowering stems which may be simple or branched, solid or hollow, and flattened or have a circular cross-section,” said Granger.
As clumps grow larger, gardeners may notice that the plant may not perform like it once did. Plants must be divided about every three years to keep them growing vigorously. Divide clumps after the blooming and growing season have ended, in late summer or early fall.
Once divided, the rhizomes will give the gardener new plants that can be located elsewhere in the garden, shared or traded with other gardeners.
Irises are afflicted by very few diseases but the iris borer (Macronocture onusta) causes serious destruction, as it devours the rhizome.
This borer is in the larval form of a moth. It may be of little consequence but it does little damage until it reaches the borer stage. Gardeners may notice yellow (rust) spots or streaks and small notches on the side of the leaves. In time, the entire leaf will dry up and wither away, as the insect consumes all the nutrients.
The borer is difficult to eradicate without using pesticides or other chemicals. Currently these commercially produced pesticides are no longer available. Other means of remediation is necessary or the plant simply will not survive.
Granger pointed out that the larvae hatch from the eggs of the adult moth and begin to burrow into the inside of the leaves. These leaves naturally grow folded, forming a natural tunnel.
The larvae eat their way down to the rhizome and hollow it out.
Organic gardeners can try using fresh parasitic nematodes. Some gardeners diligently watch for damage to the leaves where the insect enters. They then cut leaves below the damaged area. These leaves must be removed from the garden. Do not compost.
As a preventive measure, Granger suggested that gardeners follow Chuck Chapman’s (Canadian Iris Society) recommendation of an application of dormant oil spray, just as the leaves begin to grow (before the daffodils bloom).
Granger recommended spraying a 10 per cent solution of Murphy’s Oil soap as an organic alternative to Cygon.
“Clean up all iris leaves; dispose in the garbage or burn. Do not place in the compost pile (where eggs may overwinter). They will lay eggs on anything,” said Granger.
Irises are very resilient, breathtaking showpieces. Although they need sporadic maintenance, they can provide any gardener with spectacular results.
Kathy Granger’s monthly Newsletter “Home on the Grange” is just full of great tips for organic sustainable gardening. Email Kathy at thefullcirclegarden@gmail.com to get on her mailing list.
Ron Stevenson is a member of the Fergus Horticultural Society
