Bearded iris are one of the showiest of mid-summer flowers, and here’s how to grow them successfully.
There’s little point trying to grow these in shade or part shade conditions as the blooms reduce in number with shade.
But having said hat, morning shade seems to work out better than afternoon shade if you have to make a choice.
Flowers come in a wide range of colors.
Clay soils and their water holding capacity will rot the tubers out.
This plant survives in darn near any soil (other than clay) and if you toss a shovel of compost on it in the spring, it will bloom its heart out. Don’t overfertilize or you’ll create soft, lush growth that flops easily.
The number one problem with planting bearded iris is that gardeners plant them too deeply.
The main tuber should be laid on the surface and the roots coming off it should be buried in the soil.
If you cover this main tuber, you’re going to find the plant grows great leaves but doesn’t flower.
If you have a plant that doesn’t flower and you can’t see the tuber, dig it up and replant properly.
Bearded iris grow easily from seed although named hybrids will not come true.
You may find yourself with a wonderful new color!
Divide them as any other perennial. The larger the chunk of corm (storage bulbous area) you leave, the quicker it will grow to flowering size.
They also are quite easy to divide. Divide 4-6 weeks after blooming and replant immediately.
If drainage is right, this plant lives to USDA zone 3.
If you grow bearded iris, sooner or later (usually sooner) you’ll 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 tunnelling down. You’ll 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 doesn’t kill your plant, the rot will. You’ll know you’ve 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.
Preventing this problem in an organic garden simply means digging the tubers every 2 years, dividing them to remove any infected areas (burn them or destroy them – do not compost them) and watching tubers closely for any sign of damage.
Dig and clean up at the first sign (usually 4-6 weeks after blooming)
During propagation time for your growing iris, you’ll 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 you’re using them on your lawn, a few spread over on the iris bed will not be wasted.
Cleanliness is the best option here along with constant vigilance.
How To Get Ahead Of The Iris Borer
The effective method of dealing with them involves a two step process.
- Control the adults. The easiest way to do this is to hang yellow sticky traps in your garden. The adult flies will go to the traps and be
entangled in the glue. This isn’t the most scenic thing in the garden (yellow tags everywhere) but it is effective at stopping many of the adults.
- Control the grubs. The second part of control is to dig and divide your plants on a regular basis (every 2-3 years or if flowering is reduced.
Digging the corm up will allow you to look closely at all parts of the corm and carve away any eaten or rotting sections.
You can stomp any larva you find.
You can also use a beneficial nematode around the iris patch so these predator nematodes will eat the eggs.
Sanitation is critical (remove all dead and spent leaves in the fall to remove overwintering spots above ground) Remove all dead flowers when
they start to fade.
The main problem with these larvae is that they open up the iris to infection and rotting is common in infested corms.
Bacterial Soft Rot
This is a rotting away of the corm and is very often associated with the iris borer opening up and giving bacteria an entrance to the corm.
The “cure” is to control borer and sanitation.
If you have reduced flowering, then certainly examine all the corms for possible damage.
- Divide and
- Cut away any soft infected parts.
Some growers dust the wounded corms with sulfur. I never have; simply allowing them to sit for a few hours in sunlight to allow the wounds to harden up.
Note that as you’re digging, dividing and replanting you’re also increasing the size of your garden. 🙂
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.
You’ll 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.