Click below to listen to my 2 min. Garden Bite radio show: Dividing iris
Are your irises rising out of the ground? They’ve been left alone for years and are now fighting for room!
Generally it’s a good idea to divide your iris every 3 to 4 years. Dividing iris should be done 4 to 6 weeks after blooming, so sometime between July and August according to the University of Minnesota Extension. This year, 2021, it may be earlier since our plants have been blooming a little earlier with our heat wave.
First, cut the foliage fan back to about 3 to 6 inches. This will help prevent water loss, if that’s an issue. Remove yellow or dead leaves too.
Using a garden fork, dig up the rhizomes, those fatty tubers, pull apart the roots of the rhizomes after washing the clump. Cut them with a sharp knife to about 3 or 4 inches long. Take peek at this LINK to see an overgrown iris clump and how it looks at digging up and dividing. While the picture below is about dividing hosta… it’s my KNIFE I want you to notice! Nice, sharp! I saw a couple of people use a serrated edge, I would not.
If you see any mushy parts, throw them away. Don’t compost them. More on iris “issues” from the University of MN Ext.
You can trim the roots to about 2 inches.
If you’ve had issues with fungal disease, treat your rhizomes with a fungicidal powder and replant. I would suggest rinsing your tools with a 10% bleach solution after each cut to help prevent spreading of disease.
To replant your iris, loosen the soil to about 8 to 10 inches. Even though irises are planted in a shallow hole, this will allow the roots an easier time to grow. Place the rhizome so that it barely sits under the soil, firm the soil and then water it in.
Don’t mulch your iris. They need a dry period. THEN, to prevent heaving from frost and thaws, mulch AFTER the ground has frozen.
If you have no need to divide your irises, then leave the plant alone until a hard frost. At that time you can cut back the foliage. However, do remove any yellowed or dead leaves.
