Glad to have found this thread! I’m also trying tp grow capers for the first time this year. Got my seeds from Seeds of Italy, which is based in Lawrence, KS. They are the US distributor for Franchi.
Mine were stratified and were planted a couple weeks ago. Germination can apparently take 3-4 weeks, so I’m trying to be patient. 
Man I never had Capers until recently
So good a smoky like taste
Most these posts I read are for sprouting
So these need a Mederainian climate
What would be the best practice for growing in pots?
put in garage or basement for the winter to let go dorment
I am very Interested in capers Flavor
I plan to try this soon with pickling un developed Sow thistle buds
If it works for me I will abandon the idea of growing capers…
Another great treat is pickled sow thistle buds.
Simply pick flower buds before they have ever opened and drop them in leftover pickle juice. Let them soak for six weeks and they become a wonderful nibble, very similar to pickled capers.
Caper plants do not like high humidity, so if you did keep them in the basement during the too cold weather I’d use a serious dehumidifier. I see that a lot of websites rate caper bushes as being happy down to zone 8 temperatures, down to about about 7 degrees Fahrenheit, some websites even say down to zone 7 temperatures, which would be down to about -3 degrees Fahrenheit. Is the garage insulated?
I just picked some sow thistle pods (didn’t plan on it I am busy)
The jar I have here says soaked in Citrus acid
I do have acid blend for vinification (wine making) ( tartaric /malic / citrus )
I may try lemon juice , and white wine vinegar (or balsamic vinegar)
(I do have a few table spoons Red muscadine vinegar,
but that is too small the pulp is good in miso soup though (the Umami taste)
(I use the spend grape pulp of a 16 Ounce salsa jar,
and I may culture a large volume)
My basement is a constant 60 or so degree’s not Humid (how else would I age wine)
The house is over 100 years old so my garage is not insulated
(and do not want it to be)
Even so We have a patio
(one year when I was a teenager I slept in the house with the window open in winter, and it gets -20 (-28 C) for a few days a year)
I like the cold
(picture Forging Texas )
Oh Mine are a lot less opened then that (I just did so quickly)
I will see what happens
If I have time before I leave I will grab a few like that
(I have plenty of jars , and bottles for wine like odd shaped ones .)
Just tasted some out these that were more mature **
** tasted like lager beer with the acid blend.
(white vinegar tasted like white vinegar , but still not 6 weeks old)
I made a correction of acids in blend Actually wrote it right
first ingredient in acid blend is citrus malic tartaric
I am not certain how the unripe ones are doing in the acid blend
they got moldy (maybe it’s the type of jars
(from pot head friend child proof …)
I wonder if this method might work for germinating caper seeds, the cold and hot water back and forth https://www.youtube.com/watch?v=yN58RE0el3g