Iris Notes

What Should I Expect From An Iris?

First and foremost: the iris is a hardy perennial. Repeat: the iris is a hardy perennial. They do not want to die, not even in a paper bag left in the garage until February. All irises left unattended should survive until they are so massively overgrown they implode from the weight of the rhizomes.

Second, don't be seduced by the bloom, expecially in a catalogue. Here is a scale of points we use to judge the tall bearded iris in the garden a) Plant:

b) Stalk:

c) Flower:

d) Distinctiveness: 10

If we consider the bloom to the pretty face, imagine that pretty face on a stalk that is falling down drunk half the time. (Still, "Victoria Falls" won the Dykes Medal in 1984 and has subsequently obtained such a reputation.)

So don't expect a good bloom (or even a good stalk) to indicate a good iris. Especially, don't judge an it is by its performance on the show bench. A tall bearded iris may be gorgeous on the show bench, with four open blooms cleanly separated and held upright away from the stalk, but it should be considered a garden failure if it can't meet the two week requirement. What happens if the iris show is held a week later in the following years?

A good bearded iris should have a primary bloom season of at least 2 weeks, from the time the first bloom opens to the time the last bloom closes up. No modern cultival should be introduced without meeting this criterion. Either the cultival will have excellent substance or it will have many buds. The best have both.

Next, a good iris will create an attractive clump once established. As noted above, a good stalk will present its blooms to good effect; a good clump will present its stalks to good effect. The best clumps will have excellent quaternary structure - the blooms and stalks will not interfere with one another and all blooms will be above the foliage.

When the bloom season is over, the remaining leaves will still give a pleasing effect. They should be broad, clean and upright. There are several cultivars with variegated foliage - Canadian Streaker has a pale blue-violet bloom and Zebra Nights has a very dark purple bloom. I grow both in my garden and find they form very attractive clumps when positioned side-by-side. Both have won Honorable Mentions from the AIS judges.

The best irises have that extra item we call distinctiveness. An iris judge should be able to identify by name an iris displaying distinctiveness. In bloom season, an iris best displaying distinctiveness will stop trafic.

All good irises are resistant to disease.

Pests And What To Do About Them

In this area, the iris borer receives top billing. The borer is a dull, dusky, weak flying moth native to eastern North America. It lays eggs in the fall in the foliage. The egg hatches in the spring and nibbles its way into the foliage. It slowly makes its way down to the rhizome and hollows it out. It is about 2 inches long by the time it pupates.

However, it does not actually kill the iris! The iris dies due to subsequent infections, not because it has been hollowed out. If you dig the iris, then clean and bleach the rhizome (or powder it with sulphur), then let it dry for a day or so, you should be able to save the plant.

Alternatively, split the clump, destroy the infested rhizome and plant the healthiest of the remainder.

The best way to avoid the iris borer is to live in the west.

Prevention is a large part of the cure. First, keep your garden clean. Dispose of all foliage in the garbage or in the municipal recycling. A home heap will not get hot enough.

Second, look at the foliage. If you know what you are looking for, you can kill most borers when they are in the foliage. Once July rolls around, they are in the rhizome, so you just keep a sharp eye out for their telltale traces.

Third, there are predators that feed on the larvae, especially nematodes. While they are highly effective, they are also very expensive to use up here. They are not winter hardy.

Finally, there are insecticides that are effective. These should be used for large plantings. The best known is Cygon-2E; the next is Merit (unfortunately unavailable). Both are systemic, they are taken up by the plant and the pest dies upon ingestion. I have not used Merit, bit I have used Cygon-2E. My best advice is to FOLLOW INSTRUCTIONS! Iris literature suggests applying Cygon-2E as a spray when the foliage is four inches high, then again 2 and 4 weeks later. Personally, I apply it once, and then go on a borer hunt in early June.

The next insect pest is the Verbena Bud Moth. Frankly, it destroys seedpods and blossoms, not plants. There, it is a serious pest to the hybridizer, not to the average gardener.

There is no real cure for it, unless someone with expertise in snapdragons, gentians, verbenas, etc. has better information.

Thrips can be controlled with Cygon-2E, but I have never seen a thrip infestation here.

Bacterial Soft Rot occurs wherever irises grow. It rots out the rhizome such that the entire leaf fan can be lifted off the rhizome.

The infected tissue must be removed by scraping it away with a spoon, allowing the remaining tissue to dry, then dipping the rhizome in a 10% bleach solution or dusting with sulphur or any household cleaning powder.

The pathogen is a common soil bacterium (Erwinia carotovora). The best control is following good garden practices - do not wound the rhizome when weeding and don't allow the iris borer to get established.

Botrytis (Sclerotinia convoluta) is a black mould that covers the surface of the rhizome. The leaves will not grow and the clump dies. I have not heard of a cure.

Clean soil and very clean rhizomes offer the best cure. Benomyl may work, however I simply burn out the plant and the soil with a torch.