Penstemon from seed

Submitted by deesen on Thu, 01/31/2013 - 12:59

Mark/Lori if you think this would be better on a Seed thread please move it over.

I have the following Penstemon seed from the exchanges:-


Any sowing tips would be greatly appreciated.


Submitted by Tingley on Thu, 01/31/2013 - 14:40

I posted about a few other Penstemons under the Propagation thread, and was given this lead to the American Penstemon Society seed germination spread sheet:

There is a separate link to explain the terminology in the above spreadsheet:

If the above links don't work, try going to the American Penstemon Society directly at:

I nearly ordered Penstemon cobaea from Jelitto, but settled for Penstemon cyananthus, P. mensarum, and P. pinifolius. They are all planted and enjoying the ever changing winter temps here in Nova Scotia!

Submitted by HeLP on Fri, 02/01/2013 - 06:04

I have had good results this year with 3 to 4 weeks of cold moist stratification followed by 70 degree f (bottom heat).  Seeds of P. grandiflorus, roezlii, cobaea and euglaucus germinated in 3 to 5 days.

Submitted by Lori S. on Fri, 02/01/2013 - 06:32

I also cold stratify penstemons for a few weeks, and then bring them out into room temperature.  I've never used bottom heat (for anything), since my seeding area is warm enough, though I know it is very popular - I presume it's often used to increase the temp above 70 F?  

In Deno's 2nd supplement, he discusses an extensive study done by Cathey in 1969 which worked through 5 degree intervals and found optimum germination at around 70 F (20 C, or "room temperature").  It also concurs with his own studies... "temperatures above 70 are neither necessary or desirable for germination" with the exception of a couple of genera  (fresh seed of Gomphrena and possibly for Passiflora).  The conclusion was that bottom heat was unnecessary unless growing is being done in a cold place where it was the means of getting the temperature up to around 70.  I'd like to find scientific studies on the use of H2O2 on seeds... I suppose it  may help in having sort of a sterilizing function(? - against bacteria?) but I'd like to see the results of controlled experiments on whether it really enhances germination.  Can anyone post any studies for reference?

Submitted by RickR on Fri, 02/01/2013 - 09:25

Harold, your results of P. grandiflorus germination is interesting, as both Deno and the Am. Penstemon Society list it as a 40F germinator.  Perhaps it actually germinated at the end of your cold period(?).

Also gratifying is P. cobaea, where Deno lists it as a 70F +GA3 germinator, but you were successful without GA3.

Submitted by Gene Mirro on Fri, 02/01/2013 - 10:24

There are a lot of variables in the germination equation, and they differ for each genus and maybe even species.  For example, fresh seed may not require GA-3, but old seed may.  And there is light vs. dark.  Unless you are going to spend years of your life doing controlled experiments, you just find a method that works and run with it.  Maybe some of the seeds that I treat with GA-3 don't need it.  But the end result is a nice stand of seedlings with minimal extra effort.  So I just do it.  Of course, I only use GA-3 on seeds where there is evidence that it helps in some cases.  Deno's books are helpful, as are internet searches.

Watch out for Deno's 40 - 70 method.  He is only talking about germination, not growing on.  There are a huge number of plants that will germinate at 70F, then promptly die if you don't reduce the temperature.  Deno's books are not about growing seedlings; they are about germinating seed.  I know from experience that most seedlings will grow well at 60F.  So I grow all of them at that temp.  Would some grow better at 70F?  Maybe.  But I don't have the time or the facilities to fine-tune conditions for each plant, so I use the conditions that will give me success over the broadest range of plants.

On the other hand, if you are a commercial grower, and you are growing just a few species, then you need to optimize your methods for those few plants.  You will (or should) have better facilities than amateurs, and you may have employees that can share the workload.  

Submitted by Gene Mirro on Fri, 02/01/2013 - 17:25

For those who haven't grown P. cardwelli before, beware:  it can be rampant.  The stems make roots, and the plant keeps getting bigger and bigger.  It makes weeding a real challenge.  It's a good idea to put down some heavy gravel mulch before the plant really takes off.  It's perfect on a rock wall.

Submitted by Anne Spiegel on Fri, 02/01/2013 - 20:51

Penstemon cobaea self sows here abundantly.  You need to move it when it's quite small because it is growing in a deep scree where it instantly makes deep roots.

Submitted by deesen on Mon, 02/04/2013 - 12:39

Many thanks to all who responded, some very useful stuff there.