Never heard of a Hass that is that size and called mature. I have a "Mexicola"..and that for sure passes as a small sized Avocado tree. But its just a few years young..10 year,20 years from now i dont know what size it would be without pruning. And pruning may be done-read the lichee theives post. Whats the point of letting a tree grow over the fence when you will be last to the fruit?..

The first photo looks like 2 trunks, so I'm thinking you have a seedling tree. You can top work the tree by grafting a good variety on it. There are a few good You Tube videos showing exactly how to do it. I plan to do this with my seedling that isn't as old as yours, but pretty aggressive.

Well, since there's no big loss if it doesn't work, how about re-potting it in a very well draining mix, and putting it outside for more light. If it's been inside a long time, set it out in the sun slowly, like a couple hours the first day, then back in a shady spot (but still outside) more hours the second and so on over the course of a week or so. That way you'll not shock it or sunburn the leaves. Also, don't fertilize after re-potting until you see new growth, then use a good liquid citrus food at half strength. Avocados don't need a lot of humidity, they like it just fine but they don't NEED it. If they did they would not grow in areas like Southern California, which is basically a desert. So I wouldn't worry about that if I were you. And I would snip off that brown tip just past it and into the green trunk. I've found brown tips like that just keep going unless you cut them off. It might still come back, imo, 50-50% chance.

cori...perhaps my info from "fast growing tree" was a different seller...there are lots of sites with that name on the web. Don't get me wrong...Hass is a good avocado. I have 3 of them. They have derived from Guatemala not Mexico. Therefor, they are more tender than Mexicans. I am not sure about your area getting only down to the 40's or 50's in winter (9b). You need to be concerned about your 4 or 5 coldest nights of the year. That is where the danger lies. Lights in the tree does help a bit, and throwing a tarp over small trees helps even more. I know nothing about the quality/price of their trees...so I can not comment on that. If you have good experience with them....I am sure they are honest. You can sure give it a shot. Here is a good place to fine info (University of Calif)...they are not trying to sell you anything. haha Ed of Somis http://ceventura.ucanr.edu/Gardening/Garden_Info/avocado_questions/