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I am interested to know if anybody has tried the technique of stratification (cold chilling of seeds in a fridge at 2 - 5 deg C) before sowing them in Spring in order to break their dormancy and get better more even germination. I am trying this with my Dahlia seeds I collected last Oct/Nov to see if it improves Germination rates.
If you have had good or bad results please let me know. Thank you.
Dahlias come from mexico and other south american countries. they don't need stratification. They need heat. Once they are up, any frost will kill them.
My dahlia seeds that I sowed two weeks ago in a cool greenhouse have germinated and I pricked them out today.
Some plants need stratification, usually those that come from cold countries, like alpines.
I always do this with my Hemerocallis seeds, I soak them in a solution of Hydrogen Peroxide for 24hrs then put them into small ziplock bags with some damp Vermiculite & place in the fridge for 4 weeks
The usual method of stratification is to sow in Autumn, and place outside or in a cold frame for the winter. They then germinate in Spring. I find tender subjects need heat to germinate and not prolonged chilling.
Mark, what is the purpose of the hydrogen peroxide.? I have never heard of this method.
Stratification is good for a lot of hardy trees and shrubs, plants of the ranunculaceae and apiaceae families and paeonies
I leave mine outside or in a cold GH. This has worked for years but has let me down this year due to no cold period
It 's the first year I have tried Hydrogen Peroxide, it kills any mould spores on the seed & is supposed to aid germination.
Like nut, I use this method for certain seeds, particularly trees and shrubs. I'm also having to resort to the fridge this year due to lack of long enough cold spells. Acers in there at the moment.
I'm fortunate in having a fridge extension in the shed. It's full and there's still some left to go in later. If I'd known we weren't having winter this year I would have put them into narrower pots so I could get them all in
I've also got some nematodes in there but I bit my tongue when she asked what they were and said "specials" as I don't think "microscopic worms" would have gone down too well! It's probably a lot cheaper to run a fridge in an unheated shed, nut.
Much cheaper except when the sun shines in through the window Bob.
I haven't tried any nematodes yet. I tend to live with my pests. Something will eat most things
How long are you going to leave your seeds in the fridge Bob. Mine are just going into their third week and I might take them out after the weekend. Do you think that's too soon?
Most of the things I've read say six weeks but mine have been in about 4 and are coming out this weekend. If nothing happens they can always go back in..
Thanks Bob, might leave them another week. I have a second lot waiting to go in but don't want to spoil my chances with the first lot.
as the original question was about dahlias. I'll stick with that. I collected dahlia seeds on a mountainside in Southern India ( where they never have frost ) and they germinate a treat in a frost free greenhouse from March onwards.
BTW, the seed I collected was from Dahlia Imperialis: the tree Dahlia, which can reach 6 metres tall.
I've had them 2.5m in the first year, but not flowering yet.
I have a very large outdoor table, which I cover with chicken wire when all the seeds to be stratified are in place. The wire tightly holds down plastic trays of compost, the seeds themselves and a topping of vermiculite. I love watching it in freezing winds and rain, without my precious trays getting blown away, or one of my 11 cats getting at them.
The best successes I've had through stratification are the wild, or species roses. They come up all at once as soon as the weather conditions are right. I've done some trilliums this way too. Native deciduous trees are also very successful done this way (except the Oak, which I find needs to go in a warmer place to get started immediately before the winter gets going, and they seem to grow better under cover for the first winter too.
Check out Jackiegear on ebay for detailed growing instructions on her tree seeds. There are many sellers who give excellent stratification instructions, though they sometimes vary in their methods.
Used to sell some seeds pre-stratified, and they germinated very well indeed.
Update on the seeds in my fridge
Paeonia cambessedesii germinated in the fridge and Aquilegia skinneri after about 2 weeks back outside.
That's the only action from my artificial winter so far
I tried this for the first time in Feb this year with a free pack of sea holly I got from a magazine.
I left the pot in the fridge for about 5 weeks and then put them on the window sill for a few weeks. At this point I realised I didn't read the packet properly and hadn't given them the initial warm stage they were supposed to have but about half a dozen have come up
That's good Victoria, so disappointing when nothing happens.
The warm first relates to what happens naturally. It's warm when they set seed, then cold in the winter, then it's warm in the spring and they germinate.Magic