Interesting germination observation

Hello everyone. This is my first post, because frankly I haven’t felt until now that I’ve had anything to add to the conversation.

I began in the spring of 2021 to make some use of my (mostly) heirloom rose garden of perhaps 100 specimens, following the general guidelines in the RHA’s excellent publications “Rose Hybridizing For Beginners” and “The Next Step”.

One area where there doesn’t seem to be a general consensus is in the media used for stratification. But in scouring the forums, it seems the top 3 by popularity might well be paper, some form of potting soil, and sphagnum peat. Apologies to Jim Sproul using water spritz only, and Kim Rupert using nothing, maybe I can add those at a later date. Anyway, I did not come away with a clear idea of a “best practice”.

Therefore, I decided to split each of my 2021 crosses equally across those three in a controlled experiment. This is hardly an overwhelming number - 6 unique crosses, 60 total seeds - but there does seem to be a trend emerging.

All seeds were soaked 10 minutes in weak Captan solution. The media placed in Petri dishes:

  1. Canadian Peat (pH 3.5)
  2. Fertilome Seed & Cutting Mix (ca. 80% peat, 20% Perlite, dolomite and limestone added sufficient to neutralize pH, no added fertilizer)
  3. Whatman filter paper #1

The peat and “soil” were wetted with Larry Davis’ recommended 10mN calcium nitrate solution, and then arbitrarily hand squeezed until they seemed “right” and equal. The filter paper dishes each received 2ml of the solution. Distilled water was then subsequently added as necessary to maintain the same visual level of moistness.

All dishes were then kept at room temperature for 4 weeks, followed by 6 weeks in refrigerator. All dishes were then moved January 3 to my unheated garage where temps have varied from ca. 40 to 60F. First sign of germination occurred 1/15, and as of today (2/13), 25 seeds have been transferred as they germinate to flats.

Finally, here are the findings thus far:
“Soil”: 65% germination
Paper: 40%
Peat: 10%

The difference is even more remarkable when I note that the majority of these germinations occurred in the first 4 weeks, and for awhile, I thought I would have no seedlings at all from the peat. My gut feeling is that the difference between paper and soil is not statistically significant, but I haven’t crunched the numbers.

The most obvious reason seems to be the low pH of the peat somehow inhibiting germination. It certainly does seem to inhibit the growth of mold, which is prolific with both paper and soil. After all, the potting mix is largely peat itself, only pH balanced.

Admittedly, the seeds in straight peat could be late bloomers, and even exceed the success in soil, but I rather doubt it. Does anybody with more experience (which should be about everyone!) have anything to add? Am I missing something, or does anybody see a flaw in the methodology? Thanks.

The results you have obtained are definitely interesting, but, as I am sure you already know, 60 seeds are far too few to have a broad view, from a scientific point of view. It would be interesting to do so with a wider number of seeds (we’re talking about hundreds or, even better, thousands), though! Another point I’m not sure is clear is if, when you say that you split evenly the seeds, if you did so with the seeds of every cross, or just in general (each cross has a different germination potential, so if they were not split the experiment wouldn’t have much relevance, scientifically).

The last point I think is important to specify is that every seed parent is likely to have preferences in germination conditions too, making the finding of a “best medium” not precise. If you go back to species, the majority of them, growing at the limits of forests, would germinate in rotting leaves; some of them grow in open fields, where probably they germinate on the bare soil. Some others, such as rugosas, grow on shores and sandy soils, and would therefore germinate on the sand. Being modern roses a mix of many very different species, they are likely to have different preferences as well

Thanks for the input. So yes, depending on the number of seeds available for each cross, I split them equally, e.g. the largest number I had of any one cross was 15, so 5 seeds into each medium, and the lowest was 3, so just a single seed there. Where the number of seeds available wasn’t exactly divisible by 3, the remainder I handled outside of the experiment.

Your point concerning germination condition preference is a good one. So if my crosses had been majority those that prefer low pH conditions (or are perhaps very sensitive to mold…?), the results would be quite different. I get it. Of course that makes me want to learn if that condition has ever been studied as it specifically affects the germination of teas, rugosas, etc. My gut feeling is “probably not”. That doesn’t mean pH influence couldn’t be selective of different species, just that we don’t really know, right?

Because I am a novice, I have tried to absorb all the available information, and speaking generally I was able to pick out, if not that elusive “best practice”, at least a general consensus for most elements of hybridizing. Not on this particular point, though.

Also agreed that 60 points is insufficient for qualitative data, but I’m doing this solely for the enjoyment, and the opportunity to “play God” just a tiny bit. Perhaps this will be useful for fellow beginners, just understand that your mileage may vary…

Thanks Lee…as you have gleaned, there are so many options it makes our heads spin…I do appreciate your methodical approach and hope you keep on experimenting and sharing.

Thank you Lee!! I really appreciate your willingness to experiment and share. I use peat and maybe could have a better result. The polyantha roses germinate like mad in it, but others are more problematic, but that may be due to the crosses. One thing that I wonder is maybe the impact of captan and the microbes. I do get visible white fungus growing on my seeds in the peat and do not use fungicides. Maybe with the low pH and lack of a fungicide I still get enough beneficial microbe activity?? The paper and pH adjusted peat/perlite blend may just be allowing for more beneficial microbe growth and that can overcome the captan dip. It seems like during germination and when the seed coats come off (I germinate in baggies and transplant out so I can see the coats up close) they have been softened a bit and the area where the two halves come together and are stuck together by some material has broken down well. Maybe these “good” microbes are a large key to better germination and your experiment helps point to that rather than specifically the pH of peat on the rose embryos directly. Just a thought. I should try to adjust the pH of some peat and try it next year. Thank you!! With my eyes as I get older having perlite in the baggies trick my eye that there may be a radical emerging.

Never worry about communicating in rose culture. That’s what its all about! At the end of the day, its just a flower. Yet, people have built around entire cultures around “just a flower” :wink:

A pleasure to correspond with you Dr. Zlesak. I also follow you over at HMF.

I’m not sure that the soak I did in Captan did anything, really. The seeds on filter paper were covered with white mold in just a week or two. In Petri dishes, in the pH adjusted peat, it is very easy to see the white mold, and it tends to spread out around each seed over time. But there has been absolutely no signs of mold in straight peat (see picture for comparison below, some seeds have already been pricked out of the adjusted peat)

If I were to repeat all this, I would start with desiccated media, add equal amounts of water or calcium solution to each dish, then monitor water content by weight loss in the dish and periodically add back accordingly. By far, in my opinion, the most uncontrolled aspect of this experiment is the moisture content. So there’s a little voice nagging me that water availability could also factor in.

If I may ask you a question…assuming that different species of roses respond differently to pH or microbe activity, I assume the root cause is the seed coat thickness, or something due to the general morphology of the seed. My question is: in the case of a cross, is the size, shape, durability, etc. determined solely by the female plant? Or is it also influenced by the pollen?

I haven’t said much here in a long time, for various reasons. Covid distractions not disease, heavy duty gardening as a member of our community gardens board who adopted too many abandoned gardens last year, scarcity of the beautiful Newsletter to publish in, limited new ideas, and now having to move my lab to another building for university political reasons. But I thought I should mention for Lee a couple points.

I switched to vermiculite as the medium of choice because it doesn’t have acidity and lacks organic matter to sponsor microbes. I have tried extensive washing of seed (actually achenes) and couldn’t see any benefits, with or without various additives in the water. For sticky hips such as over-ripe R. canina, I do rinse off most of the goo so the seeds will mix with the medium and not clump together. Also vermiculite comes dry so I can precisely control the measured weight of that and the solution that I add to it and then weigh baggies to keep within a reasonable range if I’m feeling like they are drying out. I use 10 g vermiculite and 20 mL (grams) nitrate solution per sandwich bag, 2/3 as much for snack bags. That is 1 oz and 2/3 oz approx and a standard kitchen scale now cheaply available is quite precise enough. I try to use the larger bag for anything above 15-25 seeds, smaller one for fewer. I make batches of 200 g vermic to 400 g nitrate solution (that’s 7 oz and 14 oz), mixed in a gallon plastic bag with a good closure.

For most crosses this cold stratification medium, in a 1950s refrigerator, does not usually increase the total germination, only the speed. However for some of the more stubborn species, it does increase total germination over 2-3 years with multiple cycles of cold/warm/cold/warm at 4/2 month intervals. This cycle is similar to what von Abrams and Hand used nearly 7 decades ago for difficult crosses. They did not use nitrate though.

It turns out that for R canina and presumably its relatives, time of harvest is really important as discussed by earlier producers of rootstocks. It has to do with dormancy patterns in the seeds which can be of different kinds in different species. I am still working on this aspect with R canina over several years. Rather tedious to have to wait 3 years to get to the end of germinations. But van Fleet knew that over 100 years ago.

Temperature and its control is important, as discussed by Semeniuk and co-workers in the 1960s. For roses that like Mediterranean climates, the daily cycling seems to work well, as on the French Riviera, or parts of CA.

Somewhere on the website there is a review of most every accessible paper on the subject of germination up to around 2014. More recent papers are discussed in the Newsletter editions since that time.

Good to read you, Larry. You’ve been missed!

Thanks for this information. It is very timely for me as only today I cleaned the seeds out of a lot of Blue For You hips. When I planted a lot of Blue For You hips’ seeds in the autumn/winter of 2020, only one seedling survived and is now looking promising. Very few germinated, and of those that did many died soon afterwards.

I don’t have access to dolomite or limestone, but I do have access to either chalk or ground eggshells. I live in a hard water area known to have plenty of Calcium and Magnesium in it, but I have always grown seeds in multi purpose potting compost, usually mixed with a little Perlite. It is very fine compost with very few large bits in it, and most plants and seedlings have been fine in it, but not much luck with rose seeds except for the one Blue For You, one unknown climber that I am curious about and looking forward to it flowering, and one Rugosa type. I did lose another Rugosa from my own fault transplanting it badly. And I was reasonably lucky growing some bought Angel Wings seeds, though only a couple of the seeds germinated and many of my specimens are from cuttings from those seeds’ plants (single white flowers and semi-double pink flowers).

Would people recommend mixing ground chalk or eggshells into the mixture of multi purpose potting compost and Perlite?

The best germination I ever had was from a batch of seeds stored in a plastic sandwich bag with no media that had fallen to the bottom of refrigerator where the constant drip of cold (and hence highly oxygenated) water from the defrost cycle steadily washed over the seeds.

I fully endorse Jim Sproul’s approach of no media. Seeds are covered in a membrane (testa) that generates a steady supply of abscissic acid which diffuses into the embryo. Your goal is to wash away that abscissic acid faster than it is produced or else wait out its natural depletion. Waiting takes longer and risks infection of the seed so eliminating potential sources of infection (soil) makes sense. Kordes uses clean sand in a mist bed.

Mimicking nature means providing ‘rain’. It would not hurt to also provide some dilute calcium nitrate as a nutrient in lieu of soil as Larry has proven.

Because I live in the PNW, I did the mimick tactic about 5 years. It works to a degree. What has worked best is 3 months of ASAP basic cold stratifications, followed by planting in Jan-February in outdoor PNW climate. It’s enough steady precipitation to be enough. Only mimicking the rain has resulted in lesser germination ratios than the combinatory treatment. Unfortunate, because I prefer the laziest method possible :yum:

I once did the Winchel method on OP I collected to pick out probable selfs for race resistance reasons, and that was some horrendous germination ratios. I even separated them into half with hip matter and half 100% cleaned. Hip matter, of course, leads to germination infections in April/May, but both sets were horrendous germination ratios.

Once years ago we collected a lot of wild rose hips in the autumn, probably English dog rose Rosa canina or English field rose Rosa arvensis or some hybrid of both, and if I remember correctly we just separated the seeds from the hips and stored the seeds in glass jam jars, not in any special place or cleaning them in any special way and they were stored dry. We planted them outside the following summer and they grew with no problems.

I remember where we planted them in the garden the previous tenant had emptied the ashes from his fireplace onto the soil, so presumably that would make it very alkaline?

Larry, thank you for sharing your methods. May I ask a few questions?

  1. Did you arrive at the 10g/20ml ratio arbitrarily, or is something more behind it?
  2. David Z. mused on the possibility of beneficial microbe action, which I believe is the opposite reason you use vermiculite…any thoughts on that?
  3. Do you have any opinions on pH? I have read the Shoemaker/Carlson paper on bedding plants, and at least on filter paper, low pH seems fatal.

Thanks again.

Rosa canina and its clan is among those that have a higher defense against damp-type diseases. I have about 5 generations of Rosa canina and that has passed on readily. The species germinates like a weed. Sadly, its it’s more complex kiddos do not. Germination stabilizes to a similar rate of most moderns. Well, except this one. It germinates like a weed, and could easily germinate in littered media

I know Rosa gymnocarpa or pisocarpa (too hard to ID in the location I will describe) germinates frequently in the middle of temperate rainforest of Tillamook County. Almost in the dark depths. So it has something special going on about it (whichever of the two it is). Often found about an acre deeper that the wild huckleberries, and 2 acres deeper than salmonberries. Often in areas where we find rare, edible Chanterelle mushrooms and rare hardy orchids. That is something I highly doubt most species are capable of doing, except maybe those in rainforests of Asia.

That’s a very good bloom for a canina.

I love that rose Garhart’s Other Dog, and its parentage being described as undisclosed * Dog Father. Sounds like wonderful disease resistance.

It is, which is why I try to mention the Caninae clan often. Not for my sake, but to show others that there diseases to consider beyond black spot race resistance, powdery.

Knock Out/DKO/Blushing KO/Double Bubble, for example, passes on canker and downy quite readily. Especially canker. Nothing says gorgeous like purple blighted canes.

I have steadily used canina, pomifera, glauca, and glutinosa over the years, and they clean up these lesser diseases more often than not, which has been very helpful. I tried rubiginosa for one year, and opted out because it more drawbacks than features imo. Also, its already readily found any many roses.

I rarely put my stuff on HMF any more, and when I do its for educational purposes, which is why it says undisclosed for some things. I merely wanted to point out that working with the caninae types is quite possible. And dont worry about the initial size of these guys! I have one I kept that is a whopping 24" tall maximum. They readily adapt to modern roses with selective culling.

This study is interesting.

Does anyone here know if there any way to get these publications in PDF form?
To be clear I’m not trying to avoid paying for them of course, it’s just the whole shipping costs + time when ordering from Europe that bothers me. Other than that I’d gladly pay the hardcopy price for the publications in PDF format, if that’s an option.