Iris Borer Blues

Now is the perfect time to thin and transplant your crowded or diseased iris. If your iris have failed to bloom well, it is possible that they are overcrowded.

Dig up the rhizomes, cut off any diseased parts, cut the green leaf spears off at an angle so that the foliage forms a fan shape about 4" in height, and replant the rhizomes. It is said that iris prefer to be sunburned, which means that you shouldn't actually dig in the soil. Instead, use a trowel to dig a shallow trench and place the iris parallel to the surface of the soil. Cover the roots with soil but leave the top part of the fleshy rhizome above ground (if it were skin, it would sunburn.) Water well to get rid of air pockets, and wait patiently for next year's show.

Do NOT put mulch on or near iris!!

I have noticed that my iris foliage is in sad shape. There are dark brown oval spots over most of the foliage. That's a sure sign of the dreaded iris borer. If you look closely at the picture above, you can see the borer.

I will dig up my iris rhizome and carefully inspect it for signs of damage (a hole, rotten spots, or a tunnel like area). The iris borer is a ugly, naked pinkish-brown fat worm-like borer that has one goal in mind...eat every bit of the rhizome that it can before it must pupate then turn into a month. Rotten parts can be cut away with a clean, sharp knife that I dip in a water/bleach solution between each cut. If I do cut into an iris, I leave the rhizome unplanted for a few days so the wound can heal over. When I find a borer, I dig it out of the iris and destroy it immediately. Any damaged parts are cut away. Some people dip their iris into bleach water, but I have never done so.

Mulching iris is a no-no because the mulch overwinters the borer. I have been lax in keeping the oak and hickory leaves off of my iris in the fall and winter, so I am guilty of providing the perfect habitat for the dreaded killer borer.

Did you know that the original big portion of the iris will never bloom again? You can cut off the "fingers" of new plants that grow out the sides of t original and replant them. Put the original potato-looking piece into your compost.

I love iris, and have at least 30 varieties that I need to dig up and divide in the next few days. Luckily iris multiply well so I will be able to share the beauties with friends and family.

For more information on the iris borer and for great gardening education, go to the Master Gardener's web site at http://web.extension.uiuc.edu/state/hort.html You'll love it!

Happy gardening,

shel