Bearded irises like Blue Sapphire can be divided in September for better bloom shows in the future.
Photo by L.A. Jackson
Whether looked upon as visual workhorses or fabulous floozies in the summer landscape, bearded irises (Iris germanica) do, indeed, have the colorful blooming spunk to light up a summer garden. However, after a few years of dependable displays, established bearded iris beds can begin to fizzle in the flower power department.
What’s wrong? Too little fertilizer? Too dry? Too wet? Try too mature. As with all plants, happy, healthy bearded irises will grow and expand their root bases. This is desirable, of course, but can lead to overcrowding, which will hinder bloom production.
The easiest solution is to simply divide bearded irises. Usually done about every four years, it gives you a chance to not only revive these beauties but also share some with gardening friends. And guess what? This month is a good time to do the deed, so roll up those sleeves and get to work!
To begin, dig up the iris bed, which is easy because most of it will be close to the soil’s surface. Then, after carefully raising the rhizomes from their underworld lair, wash them and gently pull or, if necessary, cut apart, being careful not to wreck too many roots.
Now, hold out your ring finger and compare it to each rhizome, looking for ones that are about as wide with leaf blades and roots attached. They have the most potential for strong bloom production. Slightly larger rhizomes will also work, but big ol’ chubby ones are usually past their prime when it comes to delivering impressive flower displays. Rhizomes that are discolored, full of holes or squishy should be discarded.
Before replanting, snip the leaf blades back to about six inches long and also cut away any lingering flower stalks. Then, run off to find a sunny garden spot that has well-draining, heavily amended soil.
Rhizomes should be planted about a foot apart horizontal to the soil’s surface and just barely below ground—going any deeper could ding future flower production. Set the ’zomes on small mounds of dirt and spread their roots downward into the soil.
Since transplanted bearded irises will be working hard to become established this fall, help them along by watering occasionally if the rains don’t cooperate. Next growing season is a transition period, meaning their bloom shows will probably sputter, but be patient, and you will be rewarded with reinvigorated displays in the years to come.
September in the garden
• Houseplants that have vacationed outside this summer should be brought indoors before nighttime temperatures dip into the 50s. While moving them, check their leaves carefully for bugs and (especially) insect eggs—both problems waiting to happen this winter.
• Tumblin’ autumn leaves are pretty, but they can sure make a big mess in your water garden. An easy way to keep them out of a small backyard pond is to cover the surface with hardware cloth and then use a leaf blower to swoosh fallen foliage off the barrier once or twice a week.
Tip of the month
Early fall is a good time to divide herbaceous (not tree) peonies. Wait until their leaves begin to die back and then carefully dig up the peony tubers. Wash the tubers and use a sharp knife to separate them. For faster maturing divisions, make sure each one cut out has at least four or five pink, bullet-shaped "eyes," which are potential stems-to-be.
Established peonies can put on strong flower shows for 10 years or more before declining in performance. Still, they resent being yanked out of the ground—usually displaying such displeasure by blooming sparsely, if at all, the year after transplanting.
L.A. Jackson is the former editor of Carolina Gardener magazine. Contact him at lajackson1@gmail.com.