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Sunday, October 9, 2011

Pacific Coast Irises in Fall

Iris douglasiana
Fall is the time to move or divide Pacific Coast Irises.  PCI’s are very particular about the timing of root disturbance.  As many gardeners have learned, trying to divide them after spring flowering or during the summer months results in dismal failure.  Trust me on this, I’ve tried it and have been spectacularly unsuccessful.  What begins as a beautiful green fan quickly becomes a disintegrating black clump.

Iris douglasiana in the garden
Like many western native plants, Pacific Coast Irises are adapted to dry summers and moist winters.  They flower in spring at the end of the rainy season, rest during the summer months and resume active growth with the arrival of fall rains.

Lift the clump
The onset of fall moisture causes Pacific Coast Irises to form new roots that will carry them through the coming year.  PCI’s can be successfully moved and older plants can be divided and refreshed during this period.

Check for new roots
Check the readiness of your PCI’s by carefully exposing the base of the fan.  Look carefully for just emerging plump, white roots.  Plants can be divided to a single fan or moved as a larger clump.  In the weeks following transplant, these new roots will quickly penetrate the soil and you will begin to see new foliage growth at the center of the fan. 

Evergreen species like Iris douglasiana will continue to grow through the cool months that follow and reward you with a colorful display next spring.

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