AndyW

 
White-fleshed varieties are basically just muted versions of red/purple varieties. Granted, even red/purple are less 'in your face' flavor compared to many other fruits. 
 
I think you can get away with growing them to size to produce fruit in a pot that you can bring indoors for winter. 15 gallon should do the trick.

Yep, and the plants themselves are usually 20 a pop at a size you can very easily get over the spring/summer from those lil' guys. Even bigger given the right love. The issue is not knowing the flesh color. That is a big factor imo as far as culinary value goes. 
 
Of course you can always grow em out, find out its some lame white-fleshed variety, then buy and graft a red-fleshed variety onto it and get fruit production for the red quickly.

 
I have 4 dragonfruit cacti growing. Is yours red-fleshed? The white-fleshed are more bland in flavor. They're an awesome plant, and grow larger than one would expect in small amount of soil.
 
**Edit: You know those lil' columnar cactus plants with the brightly colored round cacti grafted on top you see at Home Depot/Lowes and nurseries? Those are grafted onto dragon fruit! Cut the colored ball off and it will start growing new dragonfruit branches and will eventually fruit. Super cheap way to start a dragonfruit plant... unfortunately you won't know what flesh color it is until you harvest.