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Thursday, March 24, 2011

Propagating Hardy Perennials from Seed

Ascelpias tuberosa seed capsule
Arisaema flavum berries

Sooner or later most serious gardeners dabble in plant propagation and we receive frequent requests for tips on how to grow hardy perennials from seed. While we grow hundreds of perennials from seed every season, it is important to understand that our protocol is based on our Western Oregon Zone 7b-8a climate.  In warmer climates, there may not be sufficient chill for plants that require a cold cycle to germinate and the seed may need cold stratification in the refrigerator. In colder climates than ours, seed pots and seedlings may need more protection during the most severe winter weather and some far northern gardeners have perfected the art of propagation in basements and window sills.

Succesful seed germination is a bit like finding the right key for a lock and our protocol is designed to meet the requirements of the largest range of seeds. We simply don't have the time or facilities for complicated methods so we keep it as simple as possible.

There are generally three categories of seeds; those that need a prolonged winter chill to germinate (cold germinators), those that require a period of warm temperatures to germinate (warm germinators) and those that require a bit of each to germinate (erratic germinators). To complicate matters, some seeds require multiple cycles of warm and cold while other seeds are warm germinators when the seed is fresh but become cold germinators or erratic germinators as the seed ages. The beauty of our method is that you don't have to worry about what treatment the seed requires.  This method works for nearly every species of seed we try.

Clematis integrifolia seedhead
We store seed in breathable manila envelopes in the refrigerator until the Winter Solstice or later and then sow the seed in seedpots filled with potting soil and topped with a of layer of grit or crushed rock on top. The grit protects the seeds from predation while still allowing air and light to penetrate. We have learned the hard way not to sow seed in fall because some seedlings may emerge right away and will have to be held over all winter when they are subject to die off from cold temperatures, low light, excessive moisture or dreaded damping off disease.

Seedpots in snow
Once the seeds are sown, the seedpots are put out on tables in the open air and are subjected to cold, rain, snow, sleet, hail, basically whatever mother Nature has to offer.  After a couple of months, usually by the first week of March, we begin to see tiny seedlings in some pots and we immediately move these pots to a covered area to protect the seedlings from excessive cold and moisture while providing natural light and good ventilation.  Seedlings should not be allowed to dry out and can receive a light spray of water occaisionally when needed.
Agave seedlings

Lewisia cotyledon seedlings
Over the course of the next 8 to 12 weeks, germination continues to occur in the remaining seedpots. By being left out in fluctuating spring temperatures, seeds that needs repeated cycles of warmth and cool, as well as the agitation from showers, will begin to germinate. Eventually, the weather is too warm to leave the empty seedpots exposed to strong Spring sun and we move all pots under shelter. In this location, remaining seeds that need a certain amount of sustained warmth will eventually get that and germinate, too.

There are always a few pots that do not germinate in a given season. Sometimes it is just bad seed but it may also be seed that requires multiple warm cold cycles. We set these pots aside and can see germination in them after one, two or even three more winters. Persistance and patience pays off when growing perennials from seed.


  1. it's great to see how the pros do it, and gratifying to know that my method at home is similar. I plant my seedlings in clear plastic containers and put them outside at about the same time you do, where they stay no matter how cold it gets. After they germinate the container helps to buffer temperature extremes but the seedlings aren't too coddled either. At least that's the theory, this is my first year doing this. looking forward to seeing you at the HPSO sale!

  2. Thanks, Ryan, and good luck to you in your efforts There are probably as many methods as there are growers and there is no one right way. I just hope it helps folks to have a starting point that they can further refine for their situation. And, yes, we are gearing up for the plant sale season - the HPSO sale is one of our biggest and busiest. Be sure to stop by our display and say hello!