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Have any of you rock gardeners or alpine plant enthusiasts every grown Carlina acaulis from seed?  It's a neat looking plant - and that saying a lot for a thistle! They flowers are large and impressive for such a plant.

Anyway, I have some seeds and have tried a few times to get them to germinate without success.  One website suggests that cold stratification for 60 days may do the trick.  So, I'm taking their advice and I'll either sow the seeds a pot and place them in the fridge for 2 months, or place the pot outside on the patio while the temps are above freezing.

Or, should I put them in the freezer for 60 days or keep them outside even if the temps fall below freezing?

I hope I just don't have old seed.  But, when I look at the seeds on moist soil under a loupe, they are plump, covered with fine erect hairs, and look quite happy - they just won't germinate.

Thanks much!

A friend was a market-gardener and when he was starting out, an older gardener challenged him to intentionally germinate thistle seed, just one of the usual "garden weed" species.

C. a. is native to a huge area of Europe from low to high altitudes, so at least some seed will take very low temperatures.

I strongly suspect that your C. a. are a sow (outdoors) and forget seed, just make sure the pot(s) are protected from mice, inquisitive birds and the like. If they behave like "weedy" species, they will germinate over years, not just one.

My favourite guide to seed germination is on the Ontario Rock garden society web site, it says for Carlina acaulis:

"Sow @ 20°C. Seed germinates within 3 months Requires light or the seed is very fine. Surface sow and expose to light."

https://onrockgarden.com/index.php/germination-guide/germination-guide


The PBS wiki has a list of sources on how to germinate seeds:

https://www.pacificbulbsociety.org/pbswiki/index.php/HowToGrowBulbsFromSeed


I used to spend a lot of time germinating seed, my conclusion sticking things in the fridge was never as effective as real Winter (putting them outside).

Quote from: David Pilling on December 29, 2023, 03:41:30 AMmy conclusion sticking things in the fridge was never as effective as real Winter (putting them outside)

It (the fridge, or freezer) doesn't really replicate any natural process and given that we don't really understand how germination is delayed in any detail, I would agree.
Even at the simplest level temperature isn't varying and if something needs to be washed from the seed, a fridge is not replicating rain.

I liked (but never tried) the idea of putting seeds, that need chemicals washing out to germinate, in a muslin bag in a toilet cistern - thus being exposed to random wetting and drying.

I germinated all my seeds in zip lock bags, I'm not denying that exposure to the elements in general might help, it just never applied to me - when I say real Winter is better than a fridge, that's a zip lock bag left in the garage, which would never get below zero.

Temperatures in fridges are not always what you might expect (warmer in the door). It was always the sort of dream spun by seed vendors "four weeks in a fridge to germinate".

When I was sowing large numbers of seeds, more than numerous species of hardy plants, they were always put out on what amounts to a trestle table, outside in early autumn, open to the elements.
They always got at least several fosts each winter, generally down to -3C or maybe a little lower. Some winters there was a freeze of a few days, others not.

It seemed to work OK.

The only particular seed that I remember failing with, treated like this is two species of giant Lobelia, 2 years ago. There will obviously have been others, but not quite so potentially spectacular and failures weren't that common.

Other seeds - pretty much all pot in a bag, although I sowed some Othonna yesterday and, like geophytic Pelargoniums, they require cool temperatures to germinate - they are in the unheated part of the greenhouse until frost is imminent, when they will be moved.

Quote from: David Pilling on December 29, 2023, 03:41:30 AMMy favourite guide to seed germination is on the Ontario Rock garden society web site

I purchased my seeds from a source located in Ontario, Canada.

Quote from: David Pilling on December 29, 2023, 03:41:30 AMI used to spend a lot of time germinating seed, my conclusion sticking things in the fridge was never as effective as real Winter (putting them outside).

Quote from: CG100 on December 29, 2023, 04:40:07 AMIt (the fridge, or freezer) doesn't really replicate any natural process and given that we don't really understand how germination is delayed in any detail, I would agree.

I think I'm going to place them outside for the next couple of months as opposed to putting them in the fridge. I remember reading an article about germinating Pediocactus seeds and the author was emphatic that it was necessary to have them outside exposed to the elements during winter with daily freezing and thawing and light to get them to germinate.  I suspect the same is true for Carline thistle. I'll probably place them in the garage only if the temps are going way down below freezing, just because it seems reasonable to do so. 

It's an adventure. If I can get them to germinate then I'll see if I can get them to grow here.  That will be another adventure!

I have grown pedio- and sclerocactus from seed too, and used the same "technique" - outside all winter.

I've grown unusual plants (mostly bulbs and alpines) from seed since the mid-1980s and have almost never used artificial cooling. I think temperature fluctuation has an effect on germination. Tried the toilet-tank washing technique on Iris and noticed no particular advantage. If you acquire seeds of species that would ordinarily begin their germination phase in autumn, and you don't get them until midwinter, you can sow them on arrival and they are likely to germinate the following winter/spring. Josef Halda advised letting ungerminated seed pots with species from summer-dry regions dry out during summer, and I do this with some kinds. Re. Carlina acaulis, I grew it from a Halda collection, and the most interesting thing about it is that the dry inflorescence closes during damp weather and opens back up on sunny days, even when removed from the plant! Must be an adaptation to seed dispersal.

Quote from: janemcgary on December 29, 2023, 01:50:47 PMRe. Carlina acaulis, I grew it from a Halda collection, and the most interesting thing about it is that the dry inflorescence closes during damp weather and opens back up on sunny days, even when removed from the plant! Must be an adaptation to seed dispersal.

Because of this "behavior" the plant is nicknamed the "weather thistle."

Did you grow in in pots, either outside or in your greenhouse?  Or, did you grow it in your rock garden?  Do remember what season you sowed your seeds and how long it took for them to germinate?

I have germinated C. acaulis twice.  

The first time only one came up, but there were only two viable seeds in the packet from the seed ex.  That time I planted and place the pot outside on 6 March in zone 4 where temps fluctuated from -10°C to 24°C in May.  It sprouted on 10 May.

The second time I started them inside under lights at about 21°C.  10 out of 12 seeds germinated in 7-10 days.  They were exposed to light as there was only a thin layer of grit covering them.

Quote from: Rick R. on January 05, 2024, 05:32:08 PMI have germinated C. acaulis twice. 

I have ordered some new seeds from a supplier in Canada. This vendor suggests giving these seeds a 60 day cold stratification period.  Here are their recommendations.

" Stratification improves germination, though germination can be attempted without it. If no growth within 8 weeks, place the pot in a cold area for 60 days, and then return them to room temperature for germination within 8 weeks after being brought to warmth."

Congratulations on getting your seeds to germinate.  This is a very interesting and unusual plant.  It's worth the effort to try to grow it.

Bern asked where I grew Carlina acaulis. I sowed it when the Halda seed arrived, probably late fall. The seed pots were outdoors in winter, including exposure to moderate frost. The plants were growing outdoors in a bed of pure sand, not irrigated, where I also had cacti.

Hi, it is a mountain plant (for me, "mountain" or "continental climate" means anything in zone 8 or less), so yes it needs to be stratified or a cold period outside. The winter in Virginia should be more than enough.  But if you have hot summers, expect the seedlings to die soon, unless it cools down in the night to 15 degrees or less. At least, that's what happens in the Pyrenees, where I have seen it wild. And water freely when they develop the first 2-3 true leaves.

A bit of folk-lore: the Basques call it Eguzki Lore, or Sun Flower. It was and still is hanged at the top of dwelling's doors because it was thought that if the devil or a witch passed by at night, he/she would be compelled to count the "rays" or ligules , and daylight would catch them still doing so, preventing them to do any harm. I know it's a superstition, but it is one which has survived from Pre-catholic times, so I thinks it's great. The Basque country is still a region full of misteries, and the Basques have been always reluctant to quit their traditions and beliefs. 

Carlos

I ike the tradition Carlos is writing about. If it is still done to-day it must be working as it stood the test of time.....

Carlina acaulis is also a native of the German Alps and called Silberdistel which means silver thistle.

When I was still a boy, I had sown seed of this plant in a wooden box outdoors in autumn and it was my very first experience with ,,frost or cold germination" as we call it in German. I remember that I had a lot of seedlings but not knowing better in those days I lost most of them. One thing I can say is that Carlina is an extremely tough plant forming a big and very deep tap root. So for sure it will not be happy in a pot and therefore I recommend planting seedlings into their permanent position as soon as possible. The foliage forms a large flat rosette which will choke everything too close. If you have enough seed it might be a good idea to sow some seed right where you want it to grow and label and protect the site. I still use this technique with plants that hate to be transplanted.