i think there is a houseplant forum.. but the the peeps here will probably know .. but if not... [whether it is active is always the question]

w/o tearing it apart.. when is the last time you repotted it.. how big is the pot.. how do you fertilizer.. how much sun/light does it get .. is it outdoors... can you provide a pic

and finally .... is it somehow beloved .. as in you long lost great grandmother gave it to you??? or can it be sacrificed if it doesnt all work out.. personally i dont like messing with such if they are currently growing well ..

if i understand correctly.. there is nothing wrong with this plant.. other than you want it twice as big ... are you versed enough in the latin names and IDs of various plants to be SURE.. that the tall one was exactly what the smaller one is ??? perhaps.. yours is a dwarf.. and will never get as big as the other ...

so many questions.. so little time.. ken

From my experience, dividing it isn't going to help you get a a taller plant. Sounds like it needs to be repotted.

Kinda curious about this question, too. I have a couple ponytails in large planters, too. Both had single stalks once upon a time, but a winter freeze a couple years ago changed all that. Now both have multiple shoots, which I don't mind too terribly, but would prefer one single shoot/upright/stalk. Question is, can the base be divided sucessfully.......and what would be the correct procedure?

I also have a base/root-ball/caudex, that used to be a single stalk ponytail until the same freeze. Now, for the past couple years, it is just a base with nothing growing from it. But, scratching the bark reveals a green, aparently still alive base. Is there a way to re-awaken this base?