It's the last day of summer and one of the things on my to do list today was to divide my irises. I decided that might need to become a blog post because I constantly talk to customers (I work in the garden center of our local hardware store) about why their irises aren't blooming. They always confirm the irises get at least 6-8 hours of sunlight. Sometimes it's a matter of not getting enough fertilizer (or not the right type). Most times though, when I ask when the last time they divided their irises and I get a blank stare that says "What's she talking about?" it's time for iris education.
With Irises (and most bulbs and perennials for that matter), after a few years of growing and blooming, the center part of the plant gets old and loses energy (and sometimes even dies out) yet the plant keeps putting energy into the outer areas (or newer sections). Eventually, these new and old sections are overlapping and taking up the space and energy the bloom stocks need to produce good blooms. Basically, the blooms just get crowded out from the root and foliage. So every few years (at least every 3 to 4 years) they need to be divided. Late summer or early fall is the best time to divide irises. It's not hard. Here's how:
1. Dig up the clump of irises.
2. Remove as much soil from roots as possible. At this point, I also usually cut the foliage down to about 2-3 inches above the root sections. It makes it easier to see the sections.
3. Carefully remove sections from the large clump. Use a knife or pruners if needed.
4. Cut into new sections. Make sure the new sections have at least one "fan" of leaves. Remove any withered or non-leaved sections and throw away.
You may also find some sections where one section is just sitting on top of another section. Just gently ease the two sections apart and you'll now have two new sections.
Now you're ready to plant your new iris sections.
1. Dig a shallow hole big enough to accommodate the roots (you can trim the roots some if you like).
2. Cover the roots (but not the crown where the fan of leaves emerge) with soil. Add bone meal or granular bulb fertilizer around the iris section according to package directions. You usually want a fertilizer that is higher in phosphorous than nitrogen or potassium elements to stimulate root (and bloom) growth. Say you're looking at a fertilizer package of 0-45-0. Your 1st number (0) is nitrogen. The second number (45) is phosphorous. Then, the 3rd number (0) would be your potassium.
Now that you've replanted as many new clumps as you can.....
You probably have a box full of sections to give away! Share the iris LOVE with co-workers, neighbors, friends and family. Most people are usually glad to take them off your hands. After all, they're free plants!