I’ve got quite a few germinations in pots of seeds that have just been through their second winter outside. They didn’t have any germinations last spring, so I kept them around. Now, I’m sure glad I did.
Here’s what’s new, but from two year-old pots:
(Rosa rugosa X glauca) X rugosa
Rosa carolina X arkansana
Rosa rugosa X davidii
Rosa glutinosa OP
So, don’t give up on those seemingly hopeless pots of non-sprouters.
In my 35 years of hybridizing and germinating seeds I found many times that some varieties will not germinate in the first year and some germinate better in the second year.
I read in an 75 year old rose book that some kept their seedtrays for “seven” years !! But I keep mine for just two.
When I first started, I learned from W. Kordes that seeds from some yellow parents will germinate better in their second year. I always keep my seedtrays for a second cold period. Even if there is lots of germination in the first year I have always had a few more the second time around.
I have found more germination as well to occur in subsequent years for some seed lots. One thing that I’m seeing evidence for and finally getting it is the strong beneficial effect of warm stratification before cold stratification for many species and some cultivars. By having seeds at room temperature for 2 or even 3 months before cold stratification it really syncronizes seed germination and results in a higher overall germination percent. Since we are so eager to get seeds in cold strat they generally don’t get enough of a warm strat until the summer between their first and second cold strat’s. Julie Overum looked at the effect of warm strat for her thesis on a number of species and Buck and Ag Canada germplasm. In general, R. nitida benefited from the warm strat and the cvs. were not really affected. It did not negatively effect them either. I think through generations breeders may have selected out the need for warm strat which may have been contributed by some of the species parents. The European group working with dogrose species found warm strat helps and looked at 6 weeks if I remember right. In some experiments I have done with R. eglanteria (R. rubiginosa) it appears that full benefit of warm strat is not realized until even longer than 6 weeks. I obtained >80% germination in the best treatments after the first cold strat. For the hard to germinate species which seem to germinate better in subsequent years I suggest not being so impatient in getting them into the cooler and give them a long warm strat. Remove the seeds from the hips, put them in some moist medium (I like peat), and leave them at room temp for 8-12 weeks before cold strat. and see if it helps.
I no longer use periods of warn alternated with periods of cold stratification. Instead I use the following:
I use a half sized refrigerator (which has red LEDs to promote germination) which is filled with petri dishes (containing the seeds placed ON a layer of wet sand - note the seeds are not covered by the sand) 4 layers deep. I say refrigerator but it is actually a freezer that I run at its highest setting in warm weather (about 50 degrees)or leave off in cold weather (in the winter the small amount of heat given off by the banks of red LEDs keeps the turned off freezer also at about 50 degrees F.). I use a freezer instead of a refrigerator as I did not have a use for the space that a freezer section in a normal refrigerator has. The cooling coils in this freezer are built into the shelves so I place styrofoam board on the shelves and place the petri dishes on the styrofoam.
Each day or two I check the petri dishes for germinations, and for excess or not enough moisture (excess moisture is handled by adding a little dry sand, too dry is handled by adding a little Bromelain / distilled water mixture). Using the Bromelain in water solution is based on an experiment that I did using 50 seeds which showed an increase in germination when the sand contained this type of solution.
When I check the seeds for germinations, I also moved the petri dishes one column so that they spend equal time in the various positions in the freezer.