Siberian Iris Culture

Siberian Iris originate in more Northerly climates and do not perform well as they are moved south of UDSA hardiness zone 7. Bloom stalks become shorter and plants begin to have trouble thriving.


Where to Plant

Sun or Shade?  Choose a sunny location that receives half day of sun. Siberians are more tolerant of shade than bearded iris. In Southern climates, plants will perform much better with afternoon shade.
 

Type of Soil

Siberians much prefer an organic soil with good moisture holding qualities. This does not mean boggy conditions. They do need good drainage. Soil ph should be slightly acidic to neutral (5.5-7.5)
 

When to Plant

The best time to transplant Siberians is in the fall after they after they resume growth and new roots begin to form. In some areas, early spring transplanting is also quite successful. DO NOT transplant in the heat of summer.
 

How to Plant

Plants shipped by mail should be removed immediately from their box and soaked in water overnight. DO NOT let the roots dry out. This is certain death for your new Siberian. After soaking, plant immediately in well prepared soil. Plant approximately 1 ½ inches deep. Firm soil around roots. Water in well. You may want to let the hose trickle on them for an hour or so. Once Siberians are established they will do quite well on average watering, but while they are establishing, they cannot be allowed to completely dry out. Do not fertilize newly set plants. Plants will benefit from an airy mulch.

Plant rhizomes at least 24” apart. They can be in this location for 5 to 7 years and sometimes more before dividing becomes necessary.
 

Maintenance

Controlling weeds increases the beauty of your planting and also reduces competition for nutrients. Shallow cultivation helps kill weeds and aids air circulation through the soil. Insure an adequate supply of moisture during active growth phase including and especially during bloom time. Fertilize as active growth begins in spring and again after bloom. A soil test is recommended to determine soil fertility and ph. It will also help in selecting the proper fertilizer. Without a soil test, a 5-10-10 fertilizer is a good starting point. As bloom progresses, take off spent blooms to help tidy up your garden. After bloom, remove old bloom stalks. Cut them off just above the rhizome. The leaves are quite attractive, resembling an ornamental grass. DO NOT cut off healthy leaves, they are producing food for the plant and next years bloom. In the fall, the leaves will die down completely. Leave them as a mulch until spring. In the spring as new growth begins, cut off dead leaves just above new growth. Compost or destroy the old foliage.


Dividing and Replanting

Siberian clumps usually don’t need to be divided as often as bearded iris. Bloom will be very sparse to non-existent the first year after dividing. The best bloom will be the second through the fourth or fifth years. As the clumps become crowded and bloom begins to diminish, you should consider dividing and replanting. To divide, dig the clump and wash the dirt off. With a heavy knife, separate the clump into several pieces to make it easier to work with. Divide further into pieces containing 3 or 4 rhizomes. Trim foliage back by about 2/3 to reduce stress on the plant while it is trying to grow again. DO NOT let the plants dry out completely. If not replanting immediately, leave in a bucket with water covering the roots. Plant the next day. Replenish the soil and replant as instructed earlier.


Pests and Diseases

Siberian Iris are extremely carefree once established. Aphids can sometimes be a problem and can be addressed with chemical sprays or with the introduction of predator insects.