Here in southern California, we plant iris rhizomes from October through December for April bloom. Bearded irises (Iris germanica) are fairly drought tolerant, and do well with roses and day lilies.
My morning gardening activity was to plant ten new bearded iris rhizomes. Most of my existing bearded iris are “Grandma’s Purple Flags,” the old-fashioned purple iris that Vincent Van Gogh painted, but I have a few of the newer, fancy varieties (Starship Enterprise, Vigilante, etc.) as well.
I also grow Douglas iris (Iris douglasiana) next to our pond in front. Douglas iris, a beardless iris, is a California native that grows naturally in riparian habitats. They require about 30 inches of rain a year–we get 15. So they need a bit of extra water in addition to rain.
I’m an organic gardener, and believe in preparing the soil before planting. I dig an appropriately sized hole, and add a shake of E.B. Stone bone meal and another shake of E. B. Stone Sure Start (an organic fertilizer with mycorrhizae and other beneficial soil microbes). I’m guessing that a shake from the box is about a teaspoon.
I work the fertilizer into the soil with my trowel and add water to the planting hole. I’ve seen habitat restorationists (my day job) put their plants into a dry hole, and it drives me crazy. You want the roots to go DOWN for their water. If you plant in a wet hole, the plants will have water at the bottom and the roots will grow deeply.
If you plant in a dry hole and then add water to the top after filling in the hole, the water often doesn’t get down to the bottom where the new roots are. You get a delay in plant growth at best, and death at worst. So always add water to your planting hole BEFORE adding the plant.
With irises, you don’t want to bury the rhizomes. The crown of the plant should be at the surface. Having a bit of rhizome above the soil is just fine. Position the cut fan of leaves where you want them and adjust the depth of the horizontal rhizome so that it is just barely under the surface.
I’m excited about a new iris rhizome that I received as a gift from Greenwoodgarden.com in Somis, CA. The variety is Ida Red, a deep burgandy wine color. There are no true red irises; most come in shades of blue, purple, white or yellow.
Coincidently, I had just purchased some new bearded iris varieties (Superstition, Clarence, Speeding Again, and Thornbird) from Lowe’s and was ready to plant my fall irises. I can hardly wait to see them all blooming next spring.