Dividing Pacific Coast Irises- Matilija Bob 9/29/25
Pacific coast irises have their own quickness. If you want to divide them to have more of the same iris you have to divide them when their white roots start to grow. What is all this? Okay, in summer the pacific coast irises slow their growth and in many cases their roots die back to the rhizome. If you try to divide them or replant them at this time you will likely lose them. But, in October (in our region) they begin to grow again. White roots begin to grow and they can be planted out or divided. Dividing your pacific coast irises takes a few steps but is not complicated. I guess first figure out which ones you want to divide. We pick the ones that we think customers will like in their garden that have been good growers for us. We also divide new first blooms that appear exceptional in both growth and flower. Dividing irises is the only way you can produce new ones that are identical to the parent.
Ah, now here’s what we do….After selecting the irises to divide we either dig them up from our hill where we plant them or divide them from a larger 5 gallon pot. We shake off the soil and divide the rhizomes and any remaining soil is rinsed off with water. The new rhizomes are place in a bucket of diluted hydrogen peroxide to sterilize any “evil bacteria or fungus”. We stopped using bleach years ago as it was too harsh and could burn plants, your skin, not to mention the marks it could leave on clothes. Then, the newly divided rhizomes with roots are planted out to small containers. There they sit until they have developed new roots that fill the container and then they are ready for planting in the garden. The soil mix in these small containers is mostly perlite for drainage. As long as the water runs right through the chance of rotting drops to near zero without using any chemicals. There is also a little time release fertilizer incorporated in the mix. From divisions in October to rooted out 4” pots for your garden takes about 3 months. Getting them ready for your garden in bigger takes longer and often we’ll have to hold them for almost a year to be ready to plant.
The pictures….The first picture shows the new rhizomes with their white roots. Next they are planted into small pots to root out and you can see what that looks like in the next picture. Finally, some pictures of some new “first blooms” from spring of 2025, that we’d like to start dividing – though it will take between two and three years of going through this process before we have enough to make them for sale for your garden.
Pacific coast iris rhizomes after being divided.
Rhizomes planted to 4″ pots with 70% perlite for drainage.
Some of our new “first blooms” from 2025 that we’ll be dividing.
