Don’t even try to grow an avocado tree from the pit if the pit isn’t already naturally cracked (as opposed to you cracking / cutting it) when you open the avocado. It has never worked for me unless the pit is cracked, and I find the most cracked pits in the month of July.
Then, take the pit out, gently clean off all the avocado from it. With the more rounded (or less pointy) side of the pit down, press three toothpicks (evenly spaced, horizontally) around the avocado to be able to support it in a glass of water (see below). Don’t fill the water up over the toothpicks, or they will rot and will not support the avocado pit. Within a few days to a few weeks, a taproot will start to grow (see below). During this time, make sure the water level is consistent. It must always touch and cover a little bit of the bottom of the pit.
By the way, those little things hanging out of the bottom of the pit are not roots. I always thought they were when I first started trying to grow avocados and I’d be so initially encouraged by seeing them on the pit. You can see in the picture the tap root is white and much heartier.
When your plant has nicely established roots, you can plant it in dirt. I usually use a mix of 1/2 compost from the Union Square Farmers Market and 1/2 Coast of Maine potting soil. I have made the mistake many times of planting in too big of a pot. Don’t do this! Avocados like to dry out completely between waterings and if they are in too big of a pot in the beginning, they can’t do this. Also, don’t water it too heavily in the beginning. I have made this mistake plenty of times, too.
However, I have had some great success.
My largest avocado tree is Xavier (we named all of our plants after finding really cute plant signs in the dollar bin at Target one year). He is now about 7 feet tall and growing steadily. He loses a lot of leaves in the winter, but he must be healthy as I just had blooms a few weeks ago!
Nothing came of them, though. I shook the plant, blew on the open blooms, but either Xavier wasn’t self-pollinating or I didn’t do a good enough job. Oh well, I’ve got five other avocado trees that are up and coming!