Saturday, February 5, 2011

Making Cold Stratification Easier

Over the last 2 years, I have been experimenting with the stratification process for rose seeds (this is where you give the seeds special treatment so that they have more uniform germination).  Some people do warm followed by cold stratification, but I have only used cold stratification, and it seems to work well for me.  The Rose Hybridizers’ Association (RHA) has more detailed information about rose seed stratification in their booklets on rose hybridizing, Rose Hybridizing for Beginners, and Rose Hybridizing - The Next Step (just google it).

During harvest time, hips are all collected into zip-lock bags together with other hips from the same cross.  The bag is then labeled with the cross.  What I always did in the past after the seeds were removed from the hips was to wrap them up in a paper towel (burrito style), then dip them in a large bowel of water *, carefully holding the wrapped paper towel in my hand.  Then I would squeeze out the excess water.  The damp paper towel containing the seeds would then be returned to the zip-lock bag that was labeled with the cross, and put into the refrigerator for 2 months.  This was done to simulate winter.  Note that rose seeds germinate much better after a cold period has been satisfied.  As you can imagine, if you have lots of seeds, coming from many crosses, the process of placing the seeds into paper towels, folding them, then moistening them and then placing them back into their zip-lock bags took a very long time to accomplish.  Also, since the paper towels tend to decompose while in the refrigerator, it was always quite an ordeal removing the seeds from the fragmented decomposing paper towels when it was time to plant the seeds.

Well last year, I decided to leave the seeds in the refrigerator after extraction from the hips, without putting them into the paper towels until the last 2 weeks of the cold stratification period.  I was very pleased to learn that germinations though delayed by 1-2 weeks, were just as good as the former method.  The advantage was that the paper towels did not have time to decompose, so that it was much easier getting the seeds out of the paper towels for planting.

This year I decided to try to make it even easier.  Instead of wrapping each group of seeds in a paper towel, I simply moistened a half sheet of paper towel, squeezed out the excess water and put the blob of moistened paper towel into the zip-lock bags making sure that it was in contact with the seeds.  This took half the time, and I used half the amount of paper towels.  Since I decided to do this with all of my seeds, I was a bit worried that it might affect germination.  Well, it is only 13 days since all of the seeds were planted and it appears that germination is beginning right on schedule.  I will be more certain in about 2 months whether or not germinations were adversely affected, but it looks like that will not be the case.  Stay tuned…..

* In case anyone has read my articles on my website about stratification, I have not been using Captan for the last several years.  Now, I just use plain water.


  1. Jim, it seems many of us end up on a similar path after a while: I have gradually moved in the same direction, finally abandoning paper towels entirely, as they tend to make a mushy mess by sowing time. So now I simply cut a square of double weight 8.5 X 11 paper (from my printer) and place the dampened paper in the ziploc bag. I don't clean the seeds till February, and so the paper doesn't have time to decompose in the four weeks it is in the bag. Simple, really. Thanks for sharing your methods with the rest of us!

  2. Hi Paul, that's interesting - I am glad to hear that easier works as well! I still have memories of cursing the blasted, slimy, disintegrating paper towels! I won't ever be going back to that.

  3. I'm curious, what do you mean by the paper towels decomposing? I use blue shop towels, and while they do grow black mold around the seeds, I've never had one decompose (I don't think).

  4. Hi Fa, the paper towels actually start to decompose by action of the various fungi that grow on the seeds and paper towels they are stored in. If they are left in the refrigerator for a full 8 weeks, on many of the seedling lots, the paper towels begin to fall apart when you attempt to unwrap them.

    It was way easier this year just plopping in a damp paper towel piece to provide moisture and to possibly adsorb germination inhibitors (I don't really know whether paper towels act to do this).


  5. what kind of liquid to you spray on the paper towel for germination?
    thanks for the answer

  6. Hi Connie,

    I just used plain water. Now in Winter 2011-2012, I even eliminated the paper towel and just did a small spray from a spray bottle. Germination seemed fine without the paper towel. Try it!

  7. I use sand. No clue how you get paper to work :/

  8. Hi Jankele, thank you for you comments. Since writing this blog post, I have gone to just lightly misting the seeds in the ziplock bag. Now, no paper, no mess.

  9. Hi Jim, my first time trying to stratify seeds, I moistened the paper towel and squeezed n put the seeds in bag, its been about 3 weeks and I've just noticed like a blackish mould on the outside paper not the seeds, how often or should I change the paper? Or any suggestions