Tropical glossy leaves that remain green year-round makes avocado (Persea americana) a natural choice for a houseplant. Avocados grow from the seed found in the center of the fruit. You can even use seeds from the avocados at the grocery store. Although these plants can grow to 30-foot-tall trees in U.S. Department of Agriculture plant hardiness zones 10 through 12, they remain much smaller and don't fruit when grown as a houseplant.
Seeds from store-purchased avocados require thorough washing to remove any remaining pulp before you plant them. The seeds germinate most readily in a glass of water. Inserting toothpicks around the center of the seeds, halfway between the two ends, will support the seed on the edge of the glass so it doesn't submerge fully. Set the seed on the glass rim, supported by the toothpicks, so the bottom fourth of the wider end sits in the water. Avocado seeds can take two weeks to three months to germinate when kept in a warm location away from direct light. Replenish the water in the glass as needed to maintain its depth until the seed germinates.
Transplanting the avocado to a pot improves the chances of successful growth. Allow the plant to grow in the glass until the top shoots are about 6 inches tall. Cut these shoots back to 3 inches, then transfer the seed to a pot. A 6- to 8-inch- diameter pot with a bottom drainage hole provides a suitable size for a young avocado. Plant the avocado in standard potting soil so the top of the seed sits just above the soil surface. The young plant requires gentle handling so you don't break the tender new roots or shoots. After potting, water the soil thoroughly so it's evenly moistened.
Avocados require six or more hours of indirect but bright daily sun, so place them near a brightly lit window. You can also set the plant outdoors during warm, frost-free weather. Temperatures above 60 degrees Fahrenheit produce the best growth. Avocado plants need moist but well-drained soil. Watering when the top 1 inch of soil begins to dry and allowing the excess to drain completely results in properly moistened soil. Young plants don't require fertilization, but plants more than a year old benefit from feeding. Dissolve 1/2 teaspoon of 24-8-16 fertilizer in a gallon of water, and water the avocado with this solution every two weeks in summer.
Plants grown indoors rarely suffer disease or pest problems. The plant may require support as it grows since the stems often aren't as strong as those on an outdoor-grown avocado. Tying the stem loosely to a stake that's inserted into the pot provides the necessary support so the stem doesn't bend and break. Root rot can also occur if the plant isn't properly watered. Avoid overwatering, and empty the drip tray beneath the pot within 30 minutes of every irrigation to prevent root rot.