I have a couple of avocado seedlings that I started roughly at the same time, one suspended over water and one planted in soil.
The water method seems to have worked slightly quicker, but it will soon get to the point where it needs planting on. I'm comfortable with doing that, my question is:
Should I remove the pit from the sapling? If not now, when? Or should I ever?
They are both to become house plants, not produce trees.
Sure, leave the pit attached. However I don't think you will have much luck keeping your avocado's at a foot or two in height. These plants want to become trees and exhibit a strong apical dominance. When you cut them back they put out one new leader rather than several.
If you want to keep them as house plants do not immediately put them in a big pot. Gradually increase the pot size once or twice a year or when pot bound. This will ensure that the plant does more then grow roots.
Don't remove the pit from the sapling, because the seed will provide plenty of nutrients to the tree while it keeps growing. I did this to an apple seed I got growing, and it died right after that. You should just plant the sapling as is, and let it grow out as part of the root ball.
I hope you have a 30+ gallon pot, because someone who is growing one in USDA zone 4A treats it like a seasonal plant that he puts out every year, and the root system is very big if not, you will need to trim the roots back with bonsai principles.
As per other excellent answers, no, don't remove the pit, it will likely damage or kill the tree.
As another persuasive data point, I've bought trees which have been commercially grown which still have the pits attached. Also, have a look at this video - Lynwood Avocados are New Zealands premier avocado grower - if you go to 56 seconds into the video you will see clearly that the experts leave the pits on. (Also 2:12 onwards)
