Seed stratification methods

Discussion in 'Plants: Science and Cultivation' started by Al Chomica, Nov 5, 2019.

  1. Al Chomica

    Al Chomica New Member

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    I operate a small business on Vancouver Island where I propagate plants of worth. Many get started off from seed and many of my best sellers are seeds that are normally stratified in the fridge for several months before being seeded. These include Sichuan Peppercorn, Stone Pine, Flying Dragon Orange, Angelica gigas and Paw Paws.

    The problem with some of these periods of stratification is that the seeds can sprout out of sync with the season. For example, my seeds from 2018 were stratified from Nov 2018 to March 2019 when they were deeply sown into a long pot. The seeds did not sprout very quickly but sat in the pot until July before they poked out of the soil. And then they grew very slowly from August to September when I brought them into the house under grow lights. Now they are quickly growing and are putting on an inch of vibrant leaf growth every couple days but they really should be planted in the ground instead of overwintering in a house under lights.

    My question is if anyone has heard of a method to coax the seeds into sprouting without waiting for so many months? I'm about to run experiments with the multitude of seeds I have this year and am considering soaking in Pyroligneous Acid (wood vinegar) at varying lengths of time to see if the dorman coat can be broken down any quicker.

    Any references would be appreciated...
     
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  2. Partelow

    Partelow New Member

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    Seeds of Woody Plants in North America by James and Cheryl Young, a great deal of information about native and non-native plants, including germination characteristics.
    Unfortunately, I have no silver bullet to offer you to induce germination. Scarification and acid treatments work up to a point. If species are used in forestry or environmental remediation there will exist a sure method of breaking dormancy. I have struggled for years to germinate acer griseum. One year they spontaneously germinated all over my garden. But nothing before or since. What was there about that one year? Anyways, I will continue to watch this thread and I hope some members will contribute their ideas on germination.
     
  3. Al Chomica

    Al Chomica New Member

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    Tomorrow will be the first week of soaking Paw Paw seeds in various mixtures that will hopefully induce germination. I might also try to nick the sides of a couple seeds in this experiment when I sow them. I was successful in getting some 30 year old Baobab seeds to sprout this way last year. Acer griseum? Nice trees. A place down the road called, Pacific Shores Nature Reserve has many of these gorgeous trees gracing the property that I have taken seed from. None of them ever sprouted so I can relate to your efforts. I'm going by there today and may just collect a few winged seeds to experiment with...
     
  4. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hi Al. :)
    1. When you are stratifying your seed, is that dry in the packet or in a soil medium? With seeds that normally appreciate stratification (there area many), if it doesn't seem to be working, often the cause is lack of moisture. They need the dampness of a soil medium like peat moss, coco peat, a paper towel, etc. while in the fridge to make the stratification work.
    2. Stratification often won't work on the hard seed coats unless they are scarified. I had many failures from sanding too deep into the white layer, not knowing I was damaging the seed, when I should have just barely sanded to where the white was starting to show.
    3. Make sure you are soaking your seeds before stratification to make sure they get the starting drink they need to trigger them.
    4. Sometimes it's not just the cold/damp as the trigger, but it can also be the change from the long-term cold/damp to warm damp. So after stratification in sterile media in the fridge, then the same bag of media goes up on top the fridge for some toasty summer temps. Then if only some germinate, after awhile the others can go back for another round of stratification.
    5. Many seeds have references that say they need light to germinate. That's usually not from the actual light, but the day/night hot/cold variation they get when exposed to direct sun. So these type of seeds like to really warm up hot during the day then cool off at night. It's possible to simulate that effect with timers on a heat mat. Another way is to put the already-stratified baggy right in a full south window right behind a couch where it really heats up during the day, then the window cools it off at night. As a side note, many seeds that like a very warm germination temp can possibly do even better if the temp is not constant day/night, but has natural diurnal swings.
    6. Seems like every seed's requirements differ, so for each one I germinate, I first do a Google search with genus name and "germinate", and also a separate search with the genus name and "stratification". Often you can find very specific info for that seed.
     
  5. Al Chomica

    Al Chomica New Member

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    Thank you Tom. Very appropriate info and I'm with you on the first three bullets. Perhaps even a bit more convoluted in my procedures but the seeds do get soaked and stored in a bag with cattail charcoal. The charcoal is moistened with pond water and miniscule amounts of apple cider vinegar, chitosan and lactic acid bacteria serum. These will stay in the fridge but I am also experimenting with scarification without stratification on Paw Paw seeds using different strengths of wood vinegar (pyroligneous acid). Nothing has sprouted yet but I check every day and will do some of the same with the seeds in the fridge after one month. I hadn't thought of the diurnal swings but it makes perfect sense and I'll get a couple experiments going with that idea as well.

    Now, what about freezing the seed rather than the using the warmer temp's of the fridge? I gave some Paw Paw seeds to a well seasoned gardener who said she always freezes seed to stratify...
     
    Last edited by a moderator: Nov 26, 2019
  6. Tom Hulse

    Tom Hulse Active Member 10 Years

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    That does sound convoluted! :) Do you use that generally for most of your seeds? I worry about the complex methods applied generally to all seeds, since it seems like most of them are proven on a very limited range of plants. My fear is that what may encourage one type of difficult seed may inhibit another type, especially when you're altering pH that much. The other concern would be using multiple competing methods that work against each other. For instance, the most common reasons published for using both charcoal and vinegar are very different, but they both relate back to the way they alter pH... in opposite directions. So it would seem counterproductive to use them together.
    Freezing is an interesting question! I would guess that freezing might harm or at least inhibit some tropical seed that naturally are never exposed to cold temps, but I have no facts to back that up. For the seeds that do appreciate/require stratification, there was an interesting little experiment done by one hobby grower on Delphinium, where freezing (dry) overnight more than doubled her germination from 20% to 50%, but simple regular cold/wet stratification in the fridge, no freezing at all, raised it up to 90%. So for this one limited species at least, it seems the water component was perhaps more important than freezing as a germination trigger. I would wonder if freezing might slow the water mobility towards the heart of the seed. But just knowing how many myriad different types of germination triggers there are out there, it seems like there must be some species that rely on freezing.
     
  7. Al Chomica

    Al Chomica New Member

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    Tom, the seed soaking method was taught to me by a grower who was taught natural farming techniques by Dr Higa in Japan. In my little business I sell plants of worth that can take up to two years to sprout so the medium must be sterile enough to keep the seed from rotting. It's easy to ruin a batch of Paw Paw seed because they mold quite easily. And if the seed coat dries out the embryo has died and it will never sprout so they are a bit tricky. The apple cider vinegar is in small amounts but it's purpose is to make the medium slightly acidic which doesn't favor the growth of mold. I've been doing this for three years now and am getting better success rates all the time. Three years ago I got one seed out of 50 to sprout in damp vermiculite after four months in the fridge. Two years ago I got about a dozen that sprouted by the same method.

    Last year I stratified in the cattail charcoal mix for five months. Seeds were sown in March and nothing happened until July when the little stubs started to poke out like tiny matchsticks. They didn't move aerially until September when their first leaves started to take shape. They basically establish their taproot during the two months and then they take off. Aside from the fact the slugs and pill bugs liked them too much I got about a 75% germination rate but the turnaround time is about a year and since the demand is so great for Paw Paw trees it is worth exploring different germination methods and documenting results. Also, we had a bumper crop this year on a 7-year old tree so I have hundreds of seeds to play with in all sorts of experiments.

    The seeds I grow from Angelica gigas can take up to three stratification periods spread out over a two year period. Two years ago I stratified them in vermiculite for four months and brought the tray out for a month. Three measly seeds sprouted so I pricked them out and the tray went back in the fridge for another four months. Brought out for a month, 8 seeds sprouted this time so they were pricked out and the tray went back in the fridge for another four months before coming out for a month again. And apparently this was the sweet spot I was looking at finding because all the rest of the seeds sprouted!

    Other tough seeds to sprout are Baurlach, Italian Stone Pine and Sichuan Peppercorns. I have many different experiments going on using various times, drenches and substrates. It is quite an education so thank you for sharing some of your knowledge...
     
  8. Tom Hulse

    Tom Hulse Active Member 10 Years

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    I would be unclear to me how a few drops of vinegar would acidify a mix of mainly charcoal, which is highly alkaline. The whole purpose of using charcoal, in my limited reading, has been to do exactly the same thing as vinegar, but in reverse: make the mix more alkaline to inhibit fungus and kick-start certain kinds of seeds with an abnormal pH trigger. Perhaps there are other reasons for using charcoal. I'm glad you're doing lots of experiments!

    Here is some reading I'll think you'll find interesting about the use of nitric oxide to bust dormancy in several different kinds of plants. It looks like in these new studies they are commonly getting their NO from sodium nitroprusside, so here is another set of links describing how they do that.

    Here is another exciting set of studies where they used melatonin to break dormancy. Well, exciting for germination nerds anyhow!

    I'm sure you've already heard about using gibberellic acid for seed germination. I hope you stay away from that due to the excessive elongation effects that permanently scar the plants, to the point that they can pass the flaw on to future generations. I still have a bunch of GA3 left over from 25 years ago when I first started getting crazy about germination! :)
     
  9. Tom Hulse

    Tom Hulse Active Member 10 Years

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    One more germination trigger I forgot was nitrate. Potassium nitrate seed soaks are used as a simple acid to break down the seed coat and help it take up water, but additionally, nitrate levels can be a specific internal germination trigger in some plants, especially in arid-zone winter ephemerals. It might be worth a try in some of your experiments, but as with any of these methods, make sure you are mindful of exactly what you are trying to accomplish in respect to pH, so your methods aren't working against each other.

    Also, smoke treatments & smoke water are starting to be recognized as valuable for more species than just the usual South-African or Australian plants, so it might be worth the time to research if your plants are ones affected by smoke treatments as a germination trigger.

    Another germination tip I forgot to mention was a natural fungicide to prevent damping off. Straight chamomile tea, just like you would drink it, except cold, can be used in place of your normal watering for new seeds, and as a light spritz on the surface. It allows you to keep a much wetter seed (water of course is the number one germination trigger) without losing them to fungus. It also allows you to use a more neutral or slightly acidic potting mix, which some seeds may be more receptive to, without having to use the very alkaline mix to kill fungus. I also like to occasionally use a light dusting of milled sphagnum moss on surface above the seeds, since it holds a little water nice and snug to the seed, has a color change to help me see if it is dry, and has natural antiseptic properties (sphagnum was used as a wound dressing in WWI) to also help with fungus.
     
  10. Al Chomica

    Al Chomica New Member

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    Great discussion here Tom. So many rabbit holes to dive into yet I am into a couple already. Working on your suggestions from the bottom up, the cattail charcoal acts the same way as the sphagnum does. It keeps moist by using LABS (serum from lactic acid bacteria) and apple cider vinegar. These two take care of fungal issues but I like the chamomile idea and will likely see what it does next growing season.

    On the smoke treatment, the wood vinegar is actually Pyrolignious Acid which is used as the smoke trigger for many plants in Australia. I use it to beat canker on all my fruit trees and the results were nothing short of astonishing. It is also being used as a soil drench to combat white rot but I won't know if it works until next spring when it usually kills off my garlic. Now I am using it on my seeds in various concentrations. Interesting in that the seeds soaked overnite in a 100% solution got very dark and sank to the bottom whereas the diluted concentrations left the seeds floating. Here's a rabbit hole for you to look at from Australia. Pyroligneous Acid

    I spoke to my mentor in Australia yesterday about wood vinegar. It is a household item over there and is used in the horticultural world for many purposes. I was told they now soak the WV into blotter paper, dry it out to get rid of the liquid and then they can mail it anywhere. Upon use the paper is soaked in water and the liquid then becomes Pyroligneous Acid.

    Potassium nitrate might work yes. I believe it is readily available as saltpetre here on Vancouver Island as well. Interesting link in that it discusses various soak time periods that I was also trying to work out. I think I'll try a modified version of this method with my Pyroligneous Acid as well and then stratify for six weeks. I could easily work with a six week sprouting period rather than a six month one.

    I have read about gibberellic acid and it might be my last choice to experiment with but I will try the melatonin since we have an old bottle in the medicine chest.

    The NO option you suggest and the creation of SNP to make it is beyond my level of comfort. You have kindly provided three very interesting and new avenues that I can explore and since it is raining out today I think I'll jump right in. I'll post the results of these experiments whether they succeed or not. Thank you...
     
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