How Long to Cold Stratify?

wild_rose(z8/MS)March 24, 2004

I received my Elizabeth Town Hellebore seed a month ago and they have been refrigerated in moist medium a little more than four weeks. How much longer should I wait before sowing them? Should I wait until I see germination? The outdoor daytime temps here are fluctuating between the upper 50's and 70's and at night it's in the upper 30's to mid 50's. In another couple of weeks it will be even warmer. The Dudley's recommend temps in the 50's after cold treatment, and if I wait a few more weeks the night temps won't even be that cool.

Any suggestions?

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Cold stratification for most Helleborus seed is 6-8 weeks. I believe that the 50 degree recommendation for germination is the threshold temperature, as a constant 50 degrees would be difficult to maintain, certainly not outdoors.
Here is a good site for seed germination information.

Here is a link that might be useful: Seed Germination Database

    Bookmark   March 25, 2004 at 3:57AM
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Tom Clothier's site is excellent and I've referred to it many times. The reason I mentioned that in another couple of weeks the outdoor temps would be even warmer than we're seeing now is that I was concerned that after 6 to 8 weeks, it would be too warm outside if 50 degrees was the recommended temperature to germinate the seeds after cold stratification.

At work we have a room used for long-term seed storage that stays a constant 50 degrees. It is also constantly dark. We also have a germinator that is not in use at the moment, but can't guarantee it won't be in a few weeks, or that won't be needed before the seed sprout.

I'd rather germinate these seed at home and not at work where someone else may disturb them. So 50 degrees F is the minimum temp for germination. Is there a maximum? Has anyone had experience transferring seed to 70 - 80 degree temps directly after stratifying?

    Bookmark   March 25, 2004 at 12:19PM
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claysoil(z6 PA)

My ET seeds hit week 6 in the fridge on Thursday and are sprouting like crazy. I've potted up the sprouted ones and put them outside in a shady, cool part of my yard. You are a zone ahead of me though. The hellebore seeds that I planted outside last summer are just starting to emerge so I'm in line with nature's timing.

I think the trick with temps is to get them to germinate, and after that they are not so fussy. I'd keep them in the fridge until they germ, then pot them up and put them in a shady spot based on everything I've read.

    Bookmark   March 28, 2004 at 9:35AM
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david_5311(Z 5b/6a SE Mich)

For a dummy who has no experience doing this yet, can you folks tell me exactly what you do? Wet paper towel (how wet?)? Plastic bags? I am going to do this with my own seed collected this summer. I have just potted the seed in late June and let it go through the normal summer heat and fall cool, but my germination success has been variable that way. How soon after germination do you pot up the seedlings?

    Bookmark   March 29, 2004 at 10:02AM
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Before I started my seed I did a search on this forum and came up with some great directions for germinating Helleborus seed, and now I see another thread (or is is an old one revived - I didn't check the date). Since I received my seed already heat stratified in little zipper bags containing a small amount of moist medium mixed with vermiculite, I did as another on this forum suggested and added a pinch or two of moist (not dripping wet) medium to the bag, resealed it, and placed it in the fridge. It's been five weeks now, and I'm still waiting to see germination.

David, I am certainly no expert here, or I wouldn't have posted my question. However, if you want to know the ratio of volume of water to weight of germination paper, I could give that to you, but you probably don't have any Anchor Paper on hand (I could send you some if you want :-)) and from what I've read, starting in a grow mix is better. John Dudley, the owner of Elizabeth Town Hellebores where I purchased the seed, recommends a mix composed of finely milled bark, not peat. However, his preference is based on environmental issues, not practical ones. Any type of soilless mix such as 'ProMix' should work fine. The link above to Tom Clothier's site that Razorback33 provided is excellent and will give you temperatures and times for both heat and cold stratification optimal for germination of Hellebore seed (as well as many others).

    Bookmark   March 29, 2004 at 8:57PM
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I have germination! Actually, no cotyledons have appeared yet, but the seed coats are beginning to split and the root tips are emerging from some. I went ahead and sowed all of them in gallon pots in a good potting mixture. Fingers are crossed that they'll begin popping up soon.

Thanks for the encouragement,


    Bookmark   April 11, 2004 at 9:52PM
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Sowed 01/19/2009
Refrigerated 02/04/2009

They are still in the fridge in a pot sealed in a plastic bag (today it's 05/06/2009) and they still have not germinated.

What is going wrong?

    Bookmark   May 7, 2009 at 12:10AM
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I had some seeds in the fridge last year. After several bags had sprouted, one was stubbornly unresponsive. Eventually, I concluded that nothing was going to happen, so I put them in the garage for tossing. Couldn't quite get it over my heart to throw them away though.

About 2 days later I peeked at them - and lo and behold, they had all sprouted like crazy. I planted them out and some did very well.

I have some slow sprouters this year and am contemplating taking some out anyhow - is it possible that, having had their cold period, they will respond to an increase in temperature?

    Bookmark   April 10, 2010 at 2:23PM
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morz8(Washington Coast Z8b)

Hmmmm, thought I'd answered you this morning but I don't see it.

gardenerdreaming, yes, if your seeds have rec'd the minimum 6-8 weeks moist chill, they may respond to an increase in temperature by a few/several degrees. Mine that have been exposed to a warm moist, followed by cold moist cycles of the appropriate lengths will germinate when the pots are placed outdoors where daytime temps are in the 50's, nights 40's.

    Bookmark   April 11, 2010 at 5:03PM
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