The avocado tree is a tropical plant that thrives outdoor only in warm climates (zones 9, 10 and 11 in the United States). And, unfortunately, it takes a tree planted from seed, 5 to 13 years to bear fruit.
As an indoor plant, it is unlikely your tree will live that long...although it is possible. If your plant did survive that long, you would need a very high ceiling since avocado trees grow quite tall. The point here is that your objective, as related to this article, needs to be a beautiful indoor plant, not eatable avocados.
Of course, if you live in a frost free location and are willing to wait for your tree to mature, you can use these tips to start an avocado plant indoor and transplant it to your yard. Eventually you will have avocados to eat.
Avocado leaves, bark, skin and pit are documented to be harmful to animals. Cats, dogs, cattle, rabbits, birds, fish and horses can be severely harmed or even killed when they consume them.
Negative effects in humans seem to be primarily in allergic individuals.
Source: ASPCA and wikipedia.org
In light of the above caution, if you have a dog in the house be sure the plant is out of the dog's reach. As for cats, you would need to be very vigilant since cats have the ability to climb and have a tendency to chew on house plants.
Avocado plants may be started from the seed in an ordinary avocado you buy from the store. There are several popular methods to start the seed.
Pierce the seed with toothpicks around the middle of the seed (or you can use forks) and then suspend it (pointed end up) over a glass or jar of water. Keep the bottom of the seed submerged in water.
Remove the outer (brown) skin from the seed, then put it in a zipper-type plastic bag with two tablespoons of water. Seal and place the bag in a warm location out of direct sunlight and wait. After about 3 to 4 weeks, there should be enough root growth to plant in soil. Transplant and place in a sunny spot and keep moist.
In two to six weeks, you should have a young avocado plant. However, not all avocado seeds will germinate. If your seed has not sprouted in six weeks, start over with a new seed and try again.
Use a 1 or 2 gallon pot to start your plant (or transplant if started in water). Be sure the pot has several drainage holes in the bottom. Use a light potting soil that drains well. Cactus mix works well and is available at most garden centers.
Avocados like full sun, so after your plant emerges, place in a sunny window.
The biggest cause of failure in growing avocado indoors (as well as most other plants) is over watering. Avocado plants will not tolerate wet roots. They will die if over watered. A moisture gauge is a wise investment. These devices have a probe that is pushed into the soil and a gauge that tells you if your plant needs water. Many are available at garden centers and are not expensive.
Lacking a moisture gauge, as a general rule, water your plant about every 6 weeks. When you water, place the plant in the sink and water slowly until the water runs out the drainage holes in the bottom of the pot. When the water stops draining, repeat the procedure again.
Fertilize lightly each time you water. There are fertilizers available which are designed specifically for avocado (containing zinc). But, if unavailable, you may use any general purpose house plant fertilizer.
After your plant is about a foot tall, pinch it back to half to encourage a rounder and fuller plant. Once your plant has filled it's pot with roots, transplant it to a larger pot.
With a little care and attention you can have a beautiful indoor plant that is unique and will last for years.