Allow the roots to grow inside the water-filled container until they become long enough to handle the transplant – which is at least 3 inches in length, according to Iowa State University. Planting the seed with an immature root system can lead to the seedling’s death.
Fill a quart or half-gallon container with potting mix. Use a mixture that is lightweight and has good drainage. Planting the avocado seedling into mixtures that retain water causes root rot and seedling death.
Dig a hole into the center of the container using your hands. Create a hole that is large enough to contain the root system without bunching it together. Make the hole deep enough to cover the root system and just cover the top of the seed.
Pull the germinated avocado from the water-filled container. Gently remove the seedling, being cautious not to damage the sensitive roots. Place the seed and roots into the hole and cover them with soil.
Water the transplanted avocado after planting. Irrigate until the water runs from the drain holes in the bottom of the container. Apply water regularly to keep the soil moist, but not soggy.
Situate the newly transplanted avocado outdoors in an area that receives partial shade. Place indoor transplants in a bright location. Slowly harden off outdoor transplants so they eventually tolerate full sun conditions.
Fertilize the transplanted avocado biweekly. Use a blend safe for use on houseplants. Dilute, mix and apply following the product’s instructions.