Iris Care and Growth
“”Thou art the Iris, fair among the fairest, Who, armed with golden rod – And winged with the celestial azure, bearest; the message of some God.””
– Henry Wadsworth Longfellow
Iris - a propagation primer
Irises, those tall and elegant garden standards are among the easiest to grow of all our flowers in the garden beds. One of the benefits of growing bearded iris (Iris spp.) is the ability to share them with friends or add them to other garden areas when you dig and divide them every few years. This keeps the iris performing and blooming at its peak. If left undivided, flowering decreases and the rhizome is subject to pests and damage from soft rot and borers.
Large, showy flowers appear from early spring into summer, depending on the cultivar, in all colors and color combinations, giving iris the name of rainbow flower. Bearded iris grow in U.S. Department of Agriculture plant hardiness zones 3 through 10.
Irises are relatively easy to divide and it doesn’t take much time. Just a little know how.
The following will walk you through the steps.
1 – Digging the clump
Choose a clump of irises that are relatively growing close together and showing their rhizomes jutting from the surrounding ground. If the surrounding soil is dry, water thoroughly a day or so before you dig them up. If you have more than one variety that you wish to divide, label each clump as you dig them to avoid mix ups. Use a pitch fork or spade to loosen the soil around and under the clump, being careful not to cut into the rhizomes growing near the edge. Be sure to dig deep enough to get underneath the entire mass that you are going to divide and go far enough out from this clump to avoid damaging any of the root structure of the iris mass. Then, lift the entire clump out of the ground and shake and wash away any soil adhering to the rhizomes and the root structures. I have found that the early morning hours are the best time to divide irises as the morning is cooler and therefore there will be less stress placed upon the plant when dividing occurs. however early evening would suffice also, I just advise against transplanting or dividing any plant during the heat of the mid-afternoon during the growing season.
2 – Make your cuts
The clump will consist of older and somewhat spongy rhizomes with the lighter colored newer and younger ones growing from their sides. Using a sharp knife, cut away the young rhizomes. Discard any older pieces that are undersized or diseased. Trimming the leaves to one third of their original height reduces moisture loss. Each of your cuts should consist of a firm rhizome and a fan or trimmed healthy leaves. As shown in the photo to the left, the irises are separated now into three new planting groups and have been washed off thoroughly. The dirt should also be gently removed from root and rhizome structures to allow for close inspection for any unhealthy or diseased parts.
Separate your clump into as many masses similar in size as you can and trim the leaves as shown to 1/3 of original height.
3 – Inspection
Sometimes, irises may be infested with borers. These are pinkish colored larvae (grubs with brown heads). These tunnel into and devour the rhizome tissue, often leaving a visible wound open to infection which leads to soft rot. Remove and kill all borers you find and cut away any damaged tissue. To prevent infection, you can soak the rhizomes for about 30 minutes in a 10% solution of regular household bleach, followed by a dusting of powdered sulfur. Allow the trimmed and soaked plants to dry for several hours in a shady place, giving them time to heal.
In the image to the right, on the right hand side you can see some damaged rhizomes. These will be removed, making sure to get all the damaged area when cutting. Discard this, being sure not to just toss it back into the garden beds, as disease can and will spread if done so.
Irises prefer full sun so you should alway plant irises in a sunny locale with good drainage. Dig you hole and check for borers in the soil. The new planting hole should be 25% larger than the clump going in to allow for growth. Place some potting soil on the bottom, lay the clump on this and fill in around the edges. Give them a light application of 5-10-10 fertilizer. When planting, allow for 12 to 18 inches between your new clumps. Arrange them in a triangle with their fans pointing outward and the fan of the third one pointing inwards. Do not tamp the soil but just gently place it around the root structures and rhizomes.
When I plant, I alway fill in around the root structure and then apply a light watering to naturally tamp the soil around the base of the plant, providing it with adequate support to being new growth. Then I fill in the rest or the hole and continue with my watering of the entire area. Soak it well. It sure is thirsty now.
5 – Care
Water these new plantings immediately to settle the soil around the roots. If you replant during a hot and sunny spell of continual weather, keep an eye on them and water them when dry to avoid drying out the newly planted rhizomes. Otherwise irrigate every 8 to 10 days throughout the rest of the year.