Monday, December 29, 2014

PCI Seed Germination Tricks

Kathleen Sayce

It's the wintery time of year in the northern hemisphere, when gardeners think about the coming growing season, and when iris seeds are distributed from seed exchanges. When PCI seeds are fresh, plant them immediately, and within weeks seedlings will appear. But who has fresh seeds? To send seeds to a seed exchange, they must be thoroughly dry, or they will mold in the seed packets. Alert readers will recall that I wrote about this last fall. Once PCI seeds are dry, they may have to be coaxed into germination. If those seeds are more than three years old, the coaxing might have to be pretty thorough.

PCI 'Mission Santa Cruz' is an older variety, and one I return to again and again for new seedlings.  The plants are sturdy in the coastal Pacific Northwest climate, and flower color is dark and near-red. Unfortunately, in 2014 I did not get any seed from this plant. 

Some general seed starting tips:

First, PCI seeds don't like 'warm' conditions for germination. 'Warm' when compared to many cultivated perennials is 60 F and above––in a cool to warm greenhouse, for example. PCI seeds germinate best between 40-55 F; the actual temperature varies with the species. Tenax and innominata like cooler temperatures, munzii definitely prefers the warmer end. Most hybrids germinate towards the warmer end of the range, around 50 F, though it's always better to stay on the cool side with any PCI seed lot for which the genetic source is unknown.

Second, if the seeds are truly fresh, and were not completely dried, then plant them immediately in well drained potting soil. Soak the pot with several waterings, put them somewhere bright and cool, and stand back. They will be up within weeks.

Third, if the seeds are old, particularly more than three years old, it may help to presoak them in fresh water. Presoaking can be in a dish of water, a small plastic bag, or in a mesh bag hung in the water tank of your toilet. Keeping the seeds at 40-50 F while presoaking may also help; my soaking seeds are kept in an unheated shop that stays between 40-55 degrees all winter.

Fourth, scarify them, removing some of the seed coat by gently rubbing the seeds between two sheets of fine sandpaper or scrubbing them gently in a food mill. 

A food mill is a great tool to rough up seed coats. Put the seeds in, rotate the handle 10-20 times, and shake out the bits of seed coat that were scraped off. 

I've tried one, two, three, up to thirty days of soaking, and also hung mesh bags of seeds in the water tank of the toilet. By weighing the seeds day by day as they soaked, I tracked the uptake of water, watched the seed coat loosen, and in some cases, saw the radicle (the proto-root) emerge.

Yes, those are emerging proto-roots and shoots on PC Iris seeds. They were scarified and soaked in water, and burst out of their seed coats, ready to grow. 

I wrote about these methods for the SPCNI Almanac in Spring 2012, if you would like to read about the details of my tests. [This winter the SPCNI web manager will post back issues of the Almanac and Pacific Iris on the SPCNI website ( ); past years' issues will be available to the public, including the first 40 years of the Almanac.]

Here's a new method to try––one I plan to test next year: Soak seeds in cold tea. [I decaffeinate tea at home by steeping loose tea leaves in boiling water, use a French coffee press (or a sieve), time the steep for 45 seconds, pour off the water (save it for seed soaking), add fresh hot water to steep for the cup of tea to drink.] When soaking Iris seeds, change the cold (not hot!) tea every day. For some kinds of irises, this acidic, tannin-rich water seems to help remove germination inhibitors. And it allows you to enjoy teas even when you can not tolerate caffeine––which happened to me last year very abruptly after a lifetime of drinking fully-loaded black teas.

Choices for potting PCI seeds are wide. Any container that can hold potting soil and drain off water will work. I've migrated to large rectangular styrofoam boxes (AKA fish boxes) over the past few years. I punch holes in the bottom, fill with a 1:1 mix of coarse pumice and potting soil, put the seeds on the top in rows, add labels, and a covering of chicken grit (usually granite). Then the planters go outside for the year––and no matter what the weather, they stay outside. I put them on the east side of my house where they get rain, wind, snow, a half day of sun, a rain of conifer needles, the occasional tree branch, and are close to a hose bib for summer watering. The seeds and subsequent seedlings spend a year in this container. This way, they have cool deep root runs, and are fine for their second winter. They are planted out the second spring, about 15 months after planting.

Styrofoam boxes have drain holes; there's a layer of chicken grit (in this case a reddish granite) over the top, and then wire mesh to keep the squirrels and jays from the seedlings––both of these 'varmints' like to eat sprouting Iris seeds. 

I practiced fall planting of seedlings for years, until I lost ninety percent of them a couple of years running to mid fall snow and freezing weather. Now I wait for early spring, and plant out sturdy year old plants instead.

Waiting for spring:  the next crop of PC Iris seedlings are ready to plant. Sturdy, healthy, they will be fine for the rest of winter in these styrofoam boxes, with 9-inch deep root runs and good drainage. 

My methods for seed germination are in place for the new year, including a test of a new method. What are you planning to do?  


  1. Update on the tea-soaked seeds: Both tea-soaked and freshwater-soaked seeds began to germinate in early May 2015. The tea-soaked seeds are slightly ahead of the water-soaked seeds. This seed lot was 3-4 years old, so I am very pleased with the results, and will use it again on older seed lots. Final numbers will be available by fall.


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