Although many of us have childhood memories of planting an odd-looking avocado seed in a glass of water, we often forget that the avocado plant can be moved into a pot where it will grow into a lovely tree that can live for many years. Just give it a little bit of sunshine and water, then stand back and watch it grow. Although there's a slim chance that the tree will produce fruit, it shouldn't be expected.
Save the seed from a ripe avocado. Wash the remaining bits of fruit off the seed, and soak it in a bowl of warm water overnight.
Fill a planting container with commercial potting soil. Any container will work as long as it has drainage holes in the bottom. Moisten the soil thoroughly with a spray bottle, almost to the point that it's dripping.
Remove the avocado seed from the water and plant it in the potting soil with the large end down. The top of the seed should be about 1/2 inch under the soil.
Put a clear plastic bag over the planting container, and secure it with a rubber band. Put it in a warm place in indirect light. Check the soil daily, and if it appears dry, mist it lightly, but don't soak it.
Remove the container from the plastic when the seed sprouts. Move the seedling to bright sunlight, but don't put it directly in a hot window. Continue to mist the soil when it dries out. Avocados won't do well if they're overwatered, but they do like humidity and like an occasional misting, especially during the dry, winter months.
Fertilize a mature avocado plant if the leaves begin to fall off or if they look stunted, otherwise avocados need very little fertilizer. Use a good-quality houseplant fertilizer, according to the directions on the label.
Support the avocado plant with a wooden or bamboo stake when it begins to get tall. Put the stake into the soil carefully so the roots aren't injured, and tie the plant to the stake with a strip of fabric or pantyhose.