Napa County Master Gardeners: A gift that continues, the Bearded Iris
When I was about 8 years old, my great aunt introduced me to one of my favorite flowers: the bearded iris. Not only did she share the cut flowers with me, but she instilled a love of gardening and a fascination with propagating the rhizomes.
However, I went decades without growing iris myself until my family surprised me with a Mother’s Day picnic at the Napa Iris Gardens (sadly, no longer in business). I selected a dozen or so bearded iris rhizomes that day, and they were shipped to me after harvest that fall.
Little did I know that I would eventually be dividing these plants every few years and sharing the rhizomes with anyone and everyone. From that original purchase, I have gladly shared several hundred of the progenies.
Most popular varieties of iris, including both the tall and dwarf bearded types, grow from a rhizome. A rhizome is a thick, horizontal structure that grows at or just below the surface of the soil and looks a little like a russet potato or a lobster tail. The rhizomes spread horizontally and send their roots downward into the soil. Other varieties, such as Dutch and English iris, grow from round or pear-shaped bulbs similar to a tulip bulb.
After about three growing seasons, you will notice that the plant has begun to spread and form an arch or even something close to a full circle. That’s because each rhizome grows a new rhizome on each side of the older one. Eventually the plant will form an arch or circle that can become a tangled mass. It is important to separate them then because the older rhizomes will not flower. Only the new rhizomes will generate flowers.
Wait until after the iris have finished flowering and are preparing to go dormant. The time is right when you notice the leaves dying back and turning yellow. The best time to divide iris is, unfortunately, in the height of summer, sometime between mid-July and mid-August. I like to tackle this task in the early morning or early evening to avoid the heat.
I often trim the leaves back into a 6- or 8-inch fan to make them tidier earlier in the summer before I begin digging them up to divide them.
It is usually easier to dig up a whole clump at one time with a spade or garden fork, being careful not to damage the rhizome and the roots. Shake off as much excess dirt as possible; you can even rinse the rhizomes with a hose. Then pull or snap the rhizomes apart. If they are difficult to separate, use a clean sharp knife to cut them apart.
Discard old woody rhizomes that have a stem from a previous bloom or any rhizomes that are mushy or appear rotten. Next look for the new rhizomes; those are the ones you’ll replant. They should about the size of your thumb and have a small fan of leaves attached, and they should be firm, with healthy roots. Keep them in a cool area until you are ready for planting. Place them in sawdust or raffia for air circulation if you don’t intend to replant them immediately.
In Napa Valley, you can wait until the weather cools in late September or October to plant your rhizomes. Pick a spot with rich, well-drained soil and full sun to partial shade. Set the rhizomes in the soil just above the soil line with the fan above ground.
Newly planted rhizomes will focus on root growth and building leaf fans and may not flower their first spring. Almost all healthy plants will bloom in the second year.
Whether you are planting iris for the first time, or separating and replanting them, your efforts will be rewarded the following April and May when they burst forth with color. I know it’s truly spring when my irises are in full bloom along my back fence and raised garden bed.
If you’d like to try growing iris in your garden, stop by the Bulb Booth at the Napa County Master Gardeners Fall Faire and pick up a few free rhizomes or bulbs. See below for Fall Faire details.
Become a Master Gardener: Join a group of enthusiastic local gardeners and become a UC Master Gardener of Napa County. Intimidated? No need! UC Master Gardeners do not know the answer to every gardening question, but they know how to find the answers. Register now to attend an information session about applying for the 2027 class. You must attend an information session to receive an application.
Library Talk: Join UC Master Gardeners of Napa County for a free talk on “Introduction to Bonsai, a Living Art Form” on Thursday, Sept. 3, from 7 to 8 p.m. via Zoom. Explore the history and practice of the ancient art of cultivating miniature trees to simulate full-grown trees in nature. Learn how to get started with bonsai and how to care for your living creations. Register to receive the Zoom link.
Fall Faire: Join UC Master Gardeners of Napa County on Saturday, Sept. 26, from 1 to 4 p.m. for the annual Fall Faire, an engaging afternoon featuring fun and informational booths staffed by Master Gardeners and community partners. Hands-on demonstrations and talks range from improving your soil health to designing a pollinator-friendly garden, along with plenty of friendly gardening advice. Shop for ornamental plants and winter vegetables with proceeds supporting Master Gardener programs. Enjoy food from Annie’s Lunch Box food truck and live music from the Big Ranch Rounders. The event is free and no registration is necessary.
Help Desk: The Master Gardener Help Desk is available to answer your garden questions. Use our online Plant Problem Help Form or email us at [email protected]. Include your name, address, phone number and a brief description of the problem. You can also visit us in person on Mondays and Fridays from 10 a.m. until 1 p.m. at the UC Cooperative Extension Office, 1710 Soscol Ave., Suite 4, Napa.
