Saturday, March 16, 2013

Siberian Iris
Seed germination

How to improve Siberian Iris seed germination

Siberian iris seed requires cold stratification, a chilling and drenching which removes enzymes which delay germination. This can be accomplished by sowing seeds in pots and burying the pots to the rim in the ground over winter, frost and rainfall soften the seed coat. This nearly natural process is not completely effective and may require several winters to achieve full germination of viable seeds. In the process the seed itself may loose viability. 

The artificial process described below improves the percentage of seed germination; generally well above 85%, in the first year.

I collect the mature seed pods as they begin to split open in fall.  I store the collected seed in marked envelopes, one for each cross, and let the seed dry in envelopes, placed in a cool dry location until January. Watch for fungus on the drying seed.

In January, I encase the seeds from each cross into nylons cut into squares and bundle with a color coded twist tie or rubber band. The bundles are stored in margarine containers (typically I mark the container with the crosses inside). I fill the container with tap water to the brim and burp shut.

The containers are stored in the refrigerator for at least 120 days, generally through mid-April. Typically temperatures must be between 34° and 41°F.  The water is replaced on a weekly basis. The replaced water is brownish-green, avoid splashing your eyes!

Bagged seed in container

In mid-April I broadcast the seed in pots or trays and move outdoors to germinate as high temperatures move from the 50s through 70s. I use a soil mix approximately 60 % peat moss with garden soil, planting the seed just below the surface. I water frequently and sprinkle more peat moss over exposed seed.    

To get an additional jump on the growing season I sometimes start the process earlier and germinate seed under grow lights beginning in March.

Another approach after cold stratification is to sow seed in small pots which are bagged with pieces of fruit. The ripening fruit releases ethylene gas which aids in germination.

When the seedlings are 6 to 8 inches tall they are transferred to the garden.  Space the seedlings roughly 10” apart. Some plants will bloom in the second year but nearly all will germinate in three years.

Seedling blooming two years from planting

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