Starting an avocado from an avocado purchased in the store creates a vigorous plant, but the pit does require adequate time to sprout. Allow at least a month or two to use as a school display, as the roots may not appear for three weeks or more and the sprout that produces leaves appears shortly afterward. For projects where the root system is part of the display, starting avocados in a glass of water is the obvious choice as it allows close inspection and monitoring of both root growth and the emergence of foliage.
Choose a mature avocado. Cut the avocado in half lengthwise with a knife, being careful not to cut the pit.
Pull the two halves apart. Generally, the pit will remain intact in one half of the avocado. Remove the pit by sliding a spoon behind the pit and working it free.
Wash the pit in lukewarm water to remove any fruit residue. Place on paper towel and allow to dry.
Locate the flattened area at the bottom of the pit, as this is where the root emerges. The pointy end produces the stem and leaves.
Insert three to four toothpicks spaced equally around the perimeter of the seed, about halfway between the bottom and top of the pit. Ensure toothpicks are secure and capable of holding the weight of the pit.
Fill a glass jar with tepid water. Place the seed so the bottom ½ inch rests in water and the toothpicks rest on the rim of the jar.
Place in a sunny location. Check daily and add water as it evaporates to keep the bottom of the seed covered. Watch for a small, white root from the bottom of the seed. The stem will emerge shortly and develop leaves.