Tall bearded irises are among the most dramatically beautiful flowers in our gardens, but they are not carefree. Ignore them for three or four years and the quantity of blooms will peter out, the iris patch will become crowded with their roots, and the sword-like leaves will lose their bright green youthful look.
The cure for this malaise is to renovate the iris bed every three years. You will be rewarded for your efforts with gorgeous flowers that will look fresh and forever young.
Before describing how to renovate a bed, let’s take a look at irises in general. The genus is named for the ancient Greek goddess Iris, who was the personification of the rainbow. It’s an apt name, given the full spectrum of colors in our modern irises. Because of their beauty, hybridizers have created thousands of named varieties of bearded iris over several centuries; in addition, there are several hundred wild species of irises known around the world, so the genus is vast.
The most popular and familiar kind of iris in the United States is the bearded iris, also known as the German iris. Each blossom has three upright petals called standards, and three downward-curving sepals called falls. Each fall has a “beard” that emerges from its base and lays down partway along the fall’s length, looking much like a fuzzy caterpillar.
There’s an old gardener’s saying that irises smell like their color. And there’s some truth to that. These flowers are subtly fragrant, and it’s easy enough to convince yourself that a purple iris smells like grape jelly, or a white one smells like vanilla. But before you go poking your nose down into the reproductive apparatus of an iris flower, make sure a bee isn’t already working there.
If you’re starting a new iris bed, just follow these instructions for renovating a bed, except you’ll be starting with dormant roots. Right now — the end of September and the beginning of October — is the perfect time to refresh an iris bed. Here’s what to do:
Using a spading fork, dig up the bed, shoving the tines underneath the roots and prying them up so they’re loose on the surface. Shake or thump each plant to remove most of the soil, then place them aside on a tarp or in a wheelbarrow.
Irises like summer moisture, but they don’t like to stand in water or their rhizomes (roots) may rot, so good drainage is imperative. Make a raised bed on poorly drained soil, or dig deeply to loosen hard-packed soil. Add lots of well-made, finished compost: a 6-inch-deep layer over the bed is not too much. You really can’t use too much compost. It nourishes your irises and gives fluffy texture and tilth to the soil. It also holds water like a sponge so the bed will stay moist longer during our summer drought. Dig the compost into the top foot of soil.
Now examine each plant. You’ll notice the leaves emerge from the growing end of a longer, segmented root. The part of the root where the leaves emerge will also have the freshest-looking whitish roots. The segments farthest from the growing end are remnants of previous years’ growth. Break them off the growing segment with your hands or cut them off with a sharp knife and discard them.