How important is a warm stratification period?

General Discussion
1

This article has a rather dramatic picture of the effect of a two month warm stratification on seeds of R. canina.

Most people here mention giving their seeds a warm stratification period before the cold period.

I have a few seeds that I’m going to sow tomorrow that I collected off of hips that I pollinated at the end of August and ripened inside under lights. I’m soaking them overnight (in a weak calcium nitrate solution). They all floated, so I don’t know if I’m going to get any germination no matter what I do.

I’m wondering if anyone has any info on how important it is to give your average mixed-blood rose a warm stratification period or if I could put these straight into the cooler.

2

Hi Joe,

Many years ago I did a comparison of germination methods using an enzmye treatment, compost activator, and warm and cold stratifications for varying periods of time. The roses used in the study included R. nitida, R. glauca, and pools of seeds from Buck and Ag Canada roses. What I found with respect to warm stratification was that it did not seem to make any difference to R. glauca, it greatly enhanced germination of R. nitida, and it had no effect on the modern seeds. I got much quicker germination by moving the Ag Canada and Buck pools of seeds directly into cold stratification after cleaning. I’d say go ahead and cold stratify your seeds.

3

Thanks, Julie! That’s exactly what I needed to know.

4

Joe,

7 or 8 years ago I did an experiment with some open pollinated R.arkansana seeds. I had three groups: one without warm stratification, one with two weeks and one with 4 weeks warm stratification. The group with 4 weeks warm stratification had the best germination followed by the group without any and oddly the group with 2 weeks had the poorest germination. So up until last year I gave all my seeds a period of warm stratification.

But Julie told me the results her trial so this year I didn’t use warm stratification and I haven’t noticed any change in germination rate. Even seeds from the species R.blanda and R.rugosa are germinating just fine. One thing I did different this year with the seeds is I removed them from the hips right away after harvesting them and I kept them moist in plastic baggies in the basement which is around 60 degrees until it was time for cold treatment. I don’t regard that as warm treatment becasue it was around 60 degrees whereas in the past I would warm stratify at 70 degrees or warmer. And that wasn’t the intention of it, I was just storing them until it was time for cold treatment.

5

I agree. When I first started out I didn’t know anything about a warm stratification period before a cold one. Though not scientific, I don’t think my germination rate was any different than now.

6

I’ve been using a warm stratification in part to delay germination because we have such long cold winters and it is hard to manage seedlings for me so long indoors under lights. From my experience too it seems like R. arkansana and some other North American Cinnamomeae section species and some of the Caninae section species do really benefit from warm strat before cold. It seems like from people’s experiences and comments it doesn’t typically hurt, but in some (usually rare) instances can help.

7

Thanks, David. Good to know. I can’t remember if I told you…I ended up with exactly one seed from a cross with your Lemon Fluff x (R. virg x R. laxa), and few seeds from my crosses with Orange Honey (x Frontenac and x my KOWB). I went ahead and put them into the fridge. Most of the seeds floated, so I probably picked the hips too early.

So far I have no apparent germinations from my main batch of seeds, which went in the fridge in November. It appears a constant 39 degrees F is cold enough to inhibit germination. Maybe if any have germinated they’ve just stuck their little tail down in the soil. I’m a little jealous of those people who are already potting up little seedlings, but it’s really a lot better for me to wait until we fire up the greenhouses in March or April before needing to pot up any significant number of seedlings. And it’s easy to just forget about the seedling flats until late March.

Last week I treated a few flats with a calcium nitrate solution. I divided the flat in half and used the same amount of clear water on half. It will be interesting to see if it helps germination percentages. Included were some OP High Voltage seeds…I don’t know if anyone has germinated HV before, but maybe as a yellow rose it has trouble. When I was soaking down the flats it seemed, intuitively, that the flats were thirsty and could use a good rinse. So I treated a bunch more flats with the calcium nitrate solution, sans control group. One of those flats was a bunch of Carefree Sunshine seed. I know people have had differing results germinating CS seeds, so it will be interesting to see how they germinate, in spite of the lack of a control group.

8

Joe,

I take pretty much the same approach as David. All cleaned seeds remain under room temperature stratification conditions until all hips have been collected and all the seeds have been removed from the hips. Some may have 6 weeks or more at room temperature and the last seeds collected may only have a few days. As has been noted, it never seems to hurt and in some instances , especially with some of the species, the time spent at room temperature is beneficial. Unless you are very familiar with each species and the best conditions for germination I would definitely recommend having a month or 6 weeks of room temperature stratification prior to cold and I would also recommend this for species hybrids. It may prove beneficial in that particular situation. A period of room temperature stratification also helps delay premature germination. I am happy to see germination by mid-January or early February but any earlier tends to be very stressful as seedlings must be kept under lights for too long a period. As it is I find myself constantly chopping back new growth to reduce crowding and competition for light, although this does tend to stimulate root development.Those warm temps and good growing conditions are very far away for us, although you might have us at a slight disadvantage as you will have a greenhouse up-and-running in March.

While I have not germinated OP seed from High Voltage I can tell you that seeds from crosses involving High Voltage seem to germinate readily and abundantly. They also seem to need less cold stratification time than many yellows.

I wouldn’t worry about not having germination from seeds that entered the frig in November. Trust me, when they are ready they will germinate under those conditions.

9

Finally getting round to a response to Paul- 60 is generally considered warm. Semeniuk and others did studies on temperature relationships to germination, secondary dormancy etc for several species. Details are cited in my review. As I recall, the warmer the faster, up to a critical temp then inhibition sets in. I think Don has mentioned somewhere on an earlier thread that it seems to be a competition between rates of making and breaking down ABA and GA. The two things respond differently to temps, so it changes the ratio which tips the seed into sprouting or going more dormant.

But as shown in their papers, different species may be rather different in their needs and responses.

10

If we use the definition of warm temp as 60 to 70 degrees, then everyone that stores their seeds in the hip or in a moist environment at those temps until they are ready for cold stratification is giving them a period of warm stratification. Unless the seeds are dried, stored at a cooler temp or immediately place in cold storage, they will be in warm stratification whether they realized it or not.

It’s been a while since I read the article that Joe attached and when I had I always concentrated on the results of the different temperature treatments. But there is other interesting data they report for storing the seeds:

Like this about storing the seeds in a moist environment:

“Germination the first year was found to improve if the achenes were stored in a moist medium as compared with storing dry or in the hips (Fig. 80)”

I had assumed that it didn’t matter if the seeds were stored in the hip or in a moist medium.

About the different media they used:

“Various media were tried for storing the achene’s, such as the traditional peat and sand and mixtures of the two. But far better results came from using horticultural vermiculite (“Exflor,” coarse grade) because of its light, open texture, good aeration and moisture retention.“

And this about when the hips are collected:

“However, one factor was found to exert a great influence on both total viability and speed of germination. That is the time at which the hips are harvested. Preliminary tests showed that prematurely harvested seeds (that is, those collected at any time between petal fall and while the hips are still green and the sepals fresh) gave negligible germination over four years (only 1 in 300).

On this evidence the optimum time for harvesting would seem to be as soon as the hips are fully ripe but before the flesh has begun to soften. “

"What the table shows is that the best germination is from hips that the sepals are just stating to fall off or have just fallen off. Before that or after that and the germination rates fall off dramatically. "

This is their conclusion:

“…The hips are harvested as soon as ripe in the autumn, opened without delay and the achenes cleaned out. They are stratified in tall pots (“long toms”) of moist vermiculite, screened through an appropriate sieve so that the seeds can be sifted free with ease in the spring. Two or three layers can be included in one pot. The pots are then stood in a warm glasshouse for two months and then transferred to a refrigerator at approximately freezing point for a further two months. Care is taken to dampen the vermiculite so that at no time do they dry out completely. Finally the achenes are sifted out and sown in the normal way.”

11

According to Buist (1838), a period of rest (or warm after-ripening?) can improve the germination and growth of Tea roses grown from seed.

[center]Magazine of Horticulture 4: 247-248 (July 1838)

Art. III. Experiments on the Vegetation of Rose Seeds.

By R. Buist, Florist, &c, Philadelphia.[/center]

Sir,—Some time last year I observed in your Magazine, a difference of opinion between two of your correspondents, in regard to the vegetating of rose seeds. I then determined on sowing some of the many varieties, and send you the result of my experiments.

No. 1. Seeds of Rosa indica odorata, or tea rose, were sown on the first of December, 1837, and vegetated in a temperature of between 58° and 65° Fahr., in from six weeks to three months, coming up occasionally during that period; the most of them have now bloomed, but not sufficiently strong to determine their character.

No. 2, of the same seed, and picked at the same time, was kept four weeks in sand, and sown on the ninth of January, 1838, and vegetated generally in seven weeks. The plants grew stronger and flowered better than No. 1, although treated in the same manner.

No. 3, seeds of the same, kept in sand till the first of February, and sown in pots and placed in dung or manure hot-bed, vegetated beautifully in six weeks, temperature from 65° to 75° Fahr., and are now promising, in growth, bloom and character, to surpass Nos. 1 and 2.

No. 4, seeds of Lamarque Noisette rose, collected from the plant in the open air in January, 1838, and sown along with those of No. 3, vegetated at the same time and have grown much stronger than any of the preceding, but only as yet three out of four plants have bloomed, and strange as it may appear, (you know the parent to be a large white,) one of those which flowered is a deep rose color and perfectly double. It perhaps may be desirable to say that the soil used was sand, loam, and leaf mould, in equal proportions, and watered with pure river water.