Fall is beckoning with a long list of things to do for the garden: which perennials to split, which to transplant, and what bulbs to plant. When it comes to irises, they have been on my “what to do” list since May when they, having bloomed so beautifully, started to fade. I reached out to our local expert on irises, Susanne Fuller, Iris enthusiast of the Acton Garden Club, who had given me a beautiful purple Iris with the wonderful scent of grapes, for advice on care and protection of these flowers of spring and hope. Here’s her wisdom and experience.
Anne Marie: Susanne, you have years of experience and many varieties of irises. Would you share with us a little of your story and your wisdom. How did you become so interested in irises?
Susanne – “Well, it all started many years ago, when I bought my first house in the 1970’s. My grandfather had a collection of a large variety of tall bearded irises in his garden.
“He sent two of each of many varieties to me. When I moved to Chicago, I took the irises with me. I laid them in flat trays, lined with newspaper and placed a layer of dirt on top. When I moved to Wisconsin, I took them again. They traveled with me on each of many moves. Ultimately, they came to my current home in Acton where they are flourishing.
“They are very special to me. I don’t believe I appreciated them enough at the time because I did not keep track of the names of each variety. They are not only a wonderful gift from my grandfather and a part of my heritage, but they are older cultivars, more than 50 years old and some have special characteristics such as fragrances. The purple iris has a wonderful grape scent. Few of the more recent cultivars have scents, as this has been sacrificed to other characteristics such as color or size in propagation. “
“I have learned so much about irises over the years. They come in all colors except for red. The irises I received from my grandfather are tall bearded irises, all of which require full sun as do most other types of irises, e.g. Siberian irises, Japanese irises, and Louisiana irises. However, Iris cristata and Roof Iris (Iris tectorum) are happy in part shade.”
I usually recommend the following care.
- Give irises at least half a day of sun (full sun is best), in well-drained soil; they are drought tolerant. They bloom in late May, and early June, and some have been bred to rebloom in October; those are called ‘rebloomers’.
- Plant so that the rhizome (the bulbous root) is barely covered by soil, but the roots are deep. If you bury the rhizome too deeply, the plant may refuse to flower.
- Do NOT mulch directly over the rhizomes. Mulch will tend to retain too much moisture right around the rhizomes and promote bacterial soft rot (unless you live in a hot desert climate). However, you can mulch with a layer of pine needles. The pine needles reduce weed growth and do not harm the irises.
- If you have several plants, plant them at least a foot and a half apart, “facing” the same way. The rhizomes will then increase in the same direction, without crowding each other too soon.
- Irises sometimes take a year off bloom after transplantation to settle into their new homes, so don’t be too disappointed if you don’t get bloom the spring after planting.
- If you want to fertilize, use a low-nitrogen fertilizer (6-10-10), bone meal, or superphosphate. Apply a light application in the early spring when tulips are blooming in your neighborhood, and a second light application about a month after bloom.
- Water the irises deeply once a week for the first month if there is not adequate rainfall. Avoid frequent, shallow waterings. Overwatering is another common cause of soft rot problems.
- After they bloom in spring, cut the flower stalks down close to the rhizome. In fall, cut the leaves to a short fan – 3 or 4” high. But, for the rebloomers, don’t cut the leaves down until November so that you give them a chance to bloom again even though they don’t always rebloom. Dispose of the leaves (and flower stalks). Do NOT compost them. This prevents spread of disease or borers in case you have them.
- Watch for signs of iris borers, which are like grubs that burrow into the rhizome, feasting on them from the inside, killing the plant. Borers can eat any type of iris species, but bearded varieties seem to be their favorite. Though they don’t eat the foliage, the foliage is usually their main entry point into the bulb. So, you will likely see a hole somewhere at the base of the leaves.
If you have an iris plant that is turning brown, then get down on your hands and knees to take a closer look. Here are a few sure signs of an iris borer infestation:
- Tan colored streaks on the foliage in early summer
- Leaves that turn brown in the late summer
- Holes in the leaves towards the base of the plant
- Mushy stuff that looks like sawdust around the bottom of the plant or at the tops of the iris bulbs
- Sawdust mush coming out at the base of the iris plant
- Stem of the plant is mushy and seems to be rotting
- Soft or mushy bulb that appears to be rotting
- Pinkish or tan colored worms inside of iris rhizome
- Borer hole in an iris leaf.
Once the iris borer has entered a rhizome, pesticides will have no effect on them.
To treat plants that have been affected by iris borers, take the following steps.
- Dig up a patch of infected rhizomes. It’s best to wait for the flowers to fade before checking the rhizomes. The plants move energy and nutrients upwards when they’re flowering, and digging them out will stress them further. After they bloom, you may dig them up and replant them with little impact on their health.
- Mix 1 part bleach with 9 parts water in a large bucket.
- Put the rhizomes in the water and let it sit until you see the grubs float to the surface. The grubs will come out and die.
- The bleach cleans the rhizome. Rinse off the rhizome and any remaining grubs and eggs and replant.
Finally, divide your irises every 3-5 years. Irises give you “friends” that you can give to friends.
A good source of information I recommend is Schreiner’s Gardens.
Ann Marie: Thank you, Susanne. I neatened up my garden by cutting the flower stalks this summer, and I am cutting the foliage, which I have enjoyed all summer, back to 3-4 inches this fall. I will be adding a layer of pine needles around the base. I look forward to my grape iris blossoms in the spring and some “iris friends” for my friends in the future.
Ann Marie Testarmata is the chair of public relations of the Acton Garden Club.
