It has continued to grow as expected, but zero signs of flowering. This tree was purchased from a nursery as a very young, but pre-grafted tree that should provide fruit when mature. It is about 6' tall in the container now.

I don't have any place to plant it, so it remains in the container.

Besides regular water and sun, what cultural elements are required to turn this into a fruiting avocado tree? Will it ever fruit in a 25 gallon container?

Mine flowered profusely from the get go as five gallon trees, however despite trying to cross-pollinate between the two different varieties by hand, I never got any fruit. Some formed, but always dropped off before reaching even the size of a grape. I gave up after 3 or 4 years of no fruit and constant struggle with scale insects during 6 months of year when plants had to be inside in my climate.

Pollination is definitely tricky with these guys… they must be cross-pollinated by another variety that has a different flower type (called A or B). Pollen is only released either in the morning or evening, and the stigma is receptive for a short time as well. You can look all thus up online to find a compatible partner for Haas.

Good luck!

A and B type flowers bloom irregularly if the temperatures are below 70. Making avocados self fertile in areas that are not tropical. I wouldn't worry about pollination unless the tree is indoors.

Is it hopeless unless I get a dwarf?

If that won't work, what variety of dwarf will grow in an outdoor pot and still make amazing guacamole like a haas?