Here is my experience with an avacado!
I planted one that my neighbor gave me when it was about 10 inches tall - no idea what kind.
I stuck it in the ground and paid little attention to it. After a year, it had grown to about 3 feet.
Then came the freeze of 2010 - days of 28 degrees or so.
the thing turned brown.
Long story short, I sold the house that spring so people who didn't move in for over a year and even then, took no care of the gardens I had built.
I drove by the place last week - the avocado is over 8 feet tall, green and lush!!! I have no idea if it will fruit or has fruited, but it survived cold and neglect

So take heart!
Hester

I rooted a big old avocado seed - and planted it in a pot when it was about 2 feet tall. At 3 feet, I put it in ground and it took off. At 8 feet, I tried to protect it from the freeze - but by spring, I was convinced it was totally dead. When I raked back the leaves and mulch to cut it down - I had THREE sturdy branches comeing up. It grew like crazy all summer and fall - but another winter freeze took it down. Nope, come spring, I had an avocado bush! Nearly a dozen branches popping up thru the winter detritus. By mid-summer, it was hogging the corner of the garden so I dug it up. Had to admire its tenacity, though.

Simmons is a bit less cold hardy than other similar varieties. Fine for Miami - not for Orlando. Get a Brogdon - much more cold hardy & better tasting.

Also plant your frost sensitive trees in the Spring so they get at least a full year of growth before the first winter hits.