I posted this on the post on /r/firstworldanarchists I thought I might as well post it here,it will probably get buried but I think it is kind of relevant.
So,I am procrastinating studying so naturally I was fascinated by this...
I found many articles saying that storing them together is a bad idea ((https://consumerist.com/2014/04/05/keep-your-onions-garlic-separated-and-other-tips-for-storing-fruits-vegetables/
)) BUT no source for those assumptions so digging a bit deeper I found [this](http://message.snopes.com/showthread.php?t=9290
) forum post from 2007 that links to a university of Minnesota extension service that, allegedly, states the opposite. The link however is dead and someone below comments that the link said that storing them together wouldn't make them spoil but sprout. Naturally no one quoted the link so no dice.
The WayBack machine has no snap of the page either so hit a wall there too.
After a little more digging I got this[ archived post](https://boards.straightdope.com/sdmb/archive/index.php/t-502667.html
) from 2009 that actually has a supposed quote from the page (note that temperature is measured in degrees Fahrenheit here):
> There is absolutely no truth to the story that potatoes and onions should not be stored together because one makes the other sprout. The truth is, they have different storage temperature requirements. The optimal storage temperature for potatoes is 40 degrees, the temperature at which onions sprout.
Which actually agrees with wikipedia ([Storage of potato: 4 °C (39 °F) long term and 7 to 10 °C (45 to 50 °F) before cooking](https://en.wikipedia.org/wiki/Potato#Storage
) ,[Storage of onion: room temperature so 15 -25 °C (59-77 °F)](https://en.wikipedia.org/wiki/Onion
So is it just that when storing them together most often the temperature is too high for the potatoes and the onions just survive it?That seems unlikely since storing potatoes with fruit does make them sprout even in the fridge.So temperature may be a factor but is it the deciding factor when it comes to storing potatoes with onions?
Going deeper [this](https://steamykitchen.com/42764-should-potatoes-be-refrigerated.html
) article on potato refrigeration quotes [this](http://www.plantphysiol.org/content/plantphysiol/53/4/658.full.pdf
) paper, and uses it to conclude that storing potatoes with onions or any other fruit is ill advised. The paper though is on the correlation between ethylene and potato dormancy and sprout growth.
So what produces ethylene (and what is it?) well [wikipedia](https://en.wikipedia.org/wiki/Ethylene
> [..]Ethylene is also an important natural plant hormone, and is used in agriculture to force the ripening of fruits.
> [..]Induces root hair growth — increasing the efficiency of water and mineral absorption
So it is produced when fruits to ripen but that also induces the sprouting of the potatoes.So that's why storing potatoes with apples and stuff get it to sprout but it will ,in general, make other fruit and vegetables go bad.
So do onions produce ethylene? According to[ this](http://www.tis-gdv.de/tis_e/ware/gemuese/zwiebeln/zwiebeln.htm
) hazard analysis by the transport information service
>The rate of ethylene production [of onions] is very low, being below 0.1 µl/kg*h .
and as a bonus
> Dry onions exhibit low sensitivity to ethylene, while green onions are moderately sensitive to it  (allelopathy). Onions should not as a rule be loaded together with apples or pears.
and as for potatoes
> Potatoes are moderately sensitive to ethylene . The effect of ethylene is to cause the premature onset of the sprouting process. Thus, products which release large quantities of ethylene (e.g. apples) cause potatoes to sprout prematurely (allelopathy).
So to conclude, fruit as it ripens produces ethylene gas that makes other vegetables and fruit sprout and go bad. Some produce is more sensitive to ethylene than others. So in general storing products that emit a lot of ethylene ([apples: > 100 µl/kg*h](http://www.tis-gdv.de/tis_e/ware/obst/apfel/apfel.htm
), [pears: 10 - 100 µl/kg*h](http://www.tis-gdv.de/tis_e/ware/obst/birnen/birnen.htm
), [bananas: 1 - 10 µl/kg*h](http://www.tis-gdv.de/tis_e/ware/obst/banane/banane.htm
)) with any fruit or vegetable is a bad idea. Storing onions with potatoes together is not that bad since they both produce very low amounts off ethylene but add anything else into the mix or let them sit for a very long time and the potatoes will sprout since they are moderately sensitive to ethylene while onions will do just fine.The temperature at which they are stored is of greater importance since room temperature ,while ok for storing the onions, will make potatoes sprout.
Also regarding water vapors and moisture I replied to another comment on the same post
Onions require a dry, moisture free environment to store as well.What you are referring to is (I think) self-heating. If there is a lot of moisture in the environment or there are fluctuations on the temperature or the temperature is really high, the onions will start to expel essential oils and vitamin as water vapor. This however will happen only in an environment unsuitable to store them and that by extension would be an environment unsuitable to store potatoes as well so the point is pretty much moot.
These are all conclusions i draw form the link I have above about transport service and I may very well be wrong.
Edit: allot -> a lot
^(^Allot ^is ^a ^verb, ^who ^knew...)
Edit2: Clarified temperature scales used.