Don't throw away the pit in the center of that avocado you ate for lunch. With a little cultivation, each avocado pit can become a green houseplant. Watching the seed sprout and grow is gratifying for everyone, but especially fun and educational for children.
Hold avocado pit with pointy end up. About halfway down the side of the pit, insert the straightened end of a paper clip or a toothpick about a half inch. Insert another paper clip or toothpick at the same point on the opposite side. Turn the pit and insert two more paper clips or toothpicks, opposite one another, on the remaining two sides. The supports should project from the pit like spokes on a wheel.
Place pit on the mouth of the container, and fill the container with water. Adjust the supports if necessary so the bottom third of the pit is under water; refill container daily if needed. When sprouting begins at one to two weeks, the pit will begin to split open lengthwise. Remove the brown, papery skin as it loosens.
Watch for the little green shoot to emerge from the center of the opened pit. When the shoot is about 3 inches tall, with a couple of leaves beginning to unfurl at its tip, pinch off its growing tip. Avocado plants will try to become long and leggy; pruning often, beginning in infancy, will encourage it to develop a stronger, thicker "trunk." New branches will begin to emerge on either side of the 3-inch stump.
Move the container and pit to a sunny windowsill when the next set of green leaves appear (after the first pruning). If you're office-bound and have sprouted the pit over a coffee cup, position the container under a bright desk lamp. Light will encourage the leaves to develop quickly. Prune back the new branches, but let a few tiny leaves remain.
Give the avocado plant a true home when the first true leaves are an inch or two long. Select a pot with good drainage and fill halfway with potting soil. Poke a deeper hole in the middle of the soil. Remove the avocado pit's supports and feed the long root into the hole you have created; scoop additional soil in to fill the pot and firm it around the plant. The top of the avocado pit should be exposed above the dirt. If you have sprouted more than one avocado pit, give each its own pot.
Feed the plant extra nutrients by shaking a teaspoon of houseplant food granules on top of the soil, or use plant food sticks that you push into the soil. If you use liquid plant food, place one to three drops in a cup of water and use that water to keep the plant's soil moist over the course of several days. Never put liquid plant food directly on the soil.
Keep the avocado plant in sunlight as often as possible; move it outdoors in good weather. Water often enough to keep soil evenly moist. Keep pruning and moving to larger containers as it grows; if you live in a warm climate, plant it in the ground outdoors, in an area where it will have room to grow.