I am assuming that the example you referred to as Climbing Onion is what I think of as a Ponytail Palm?? If so, we had one that grew huge in a pot indoors. My mom had one growing on her property in Florida that was about 10 ft. tall!. ...razor sharp edges on the green fronds!!
A climbing onion is Bowiea... a small bulb with green-hair-like growths out the top that vine. A Ponytail palm is an Agave relative that grows into a massive plant, up to 20 feet wide at the base and nearly as tall. The two are completely unrelated.