Growing Iris
When you think of iris, the odds are youre thinking of Bearded Iris. These fragrant plants with their huge blowsy flowers have captured the hearts of many an unwary gardener and like many love affairs, theres a broken heart or two strewn along the way.
Bearded Iris
Bearded iris come in several different heights and if you live in a windy area, you are well advised to avoid the tall bearded varieties because they are quite susceptible to wind damage (and rain damage) unless you want to securely stake them.
I grew to enjoy the mid and short bearded plants very much. Because Im a lazy gardener, I put my taller bearded varieties in the back of the garden next to sturdy perennials that would support the flower stalks.
Growing Iris
Growing iris demand full sun or very light shade in a well drained soil. Soils that hold moisture will rot out the rhizome over the winter leaving you with a mushy, yellow slime instead of a firm root. Growing iris is not a problem into USDA zone 3.
Propagation is usually 6-8 weeks after blooming when the rhizomes are divided leaving a chunk of rhizome and roots to every new division. These are very tough plants and division is done with a shovel and a strong arm. Whacking off a bit of a plant to share or increase your own flower show is a firmly established tradition in the garden world. The only caveat to this is to plant the rhizome so the fleshy part is showing while the trailing roots on the bottom are well buried. If you plant the rhizome too deeply, it will grow like mad but not flower
If your growing iris... well, stops flowering or reduces the number of blooms it is producing, dig and divide it. This will happen every few years.
There are two problems associated with growing iris that youll eventually see. The first is the dreaded iris borer and the second thrips.
Iris Borer
If you grow bearded iris, sooner or later (usually sooner) youll see this iris borer. The borer eggs overwinter on plant debris or on the crown of the iris plant (eliminate all plant debris in the fall).
In the spring, the tiny caterpillars hatch out and climb up the leaves to chew a small pinprick of a hole in the leaf. They eat themselves into the center of the leaf and start tunneling down. Youll see a small pinprick damage area and brown streaks extending downward from the pinprick as the borer works its way down through the center of the leaf. The leaf tips will likely go brown if there are enough of them. By the middle of the summer, the borers are now 2 inches long and are at the rhizome where they begin to tunnel and eat.
The tunnels they create are perfect sites for bacterial soft rot to invade so if the borer doesnt kill your plant, the rot will. Youll know youve got iris bacterial soft rot because the root will go soft, mushy and really foul smelling.
In late August the caterpillars pupate, turn into moths and these moths lay eggs on plant debris to complete the cycle.
The cure is constant attention. Inspect the iris every summer for damage. Look for spotting (dark spots on the leaves) and once these spots are seen on the leaves, look carefully at the rhizome. During propagation time for your growing iris, youll have to dig up the rhizome to cut out the damaged areas and kill off the borer. (step on it) There is no organic spray that will act inside the plant and kill off the protected borer (it's inside the plant hidden safely away).
Dusting the plant in early spring with diatomaceous earth has been shown to be somewhat effective in controlling the caterpillar stage.
Late summer and early fall sanitation is critical to preventing egg laying sites. Clean up all iris bed areas immediately after the first killing frost to eliminate any overwintering eggs.
Nematodes have been shown to be quite effective at attacking the pupating borers so if youre using them on your lawn, a few spread over on the iris bed will not be wasted.
Thrips
Thrips are tiny flies that lay their eggs in the developing buds and when the eggs hatch out, the larva scrape away at the flower surface.
Youll know you have thrips because your flower will be mottled and / or streaked or will not even open up but appear to be rotting. Control thrips by spraying with insecticidal soap or dusting with diatomaceous earth or rotenone as soon as you see the buds starting to form. Blue sticky cards hung in the garden attract flying adult thrips and control is quite good with these.
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