Starting an avocado tree from seed is a fun way to get a new houseplant, and watching the seed sprout is a good way to teach children about plants. Avocado seedlings bear fruit in five to seven years, but container-grown, indoor plants rarely blossom or fruit. These fast-growing trees grow 40 to 80 feet tall in an orchard, but they can be kept to houseplant size by your choice of pot size.
Avocados can start in a pot as small as 6 to 8 inches, but you'll need to "pot them up" to a larger size every year or two.
Starting Avocados Indoors
Avocado seeds sprout easily both in water and in soil. To start a seed in soil, choose a 6- to 8-inch pot filled with a mix of potting soil, humus and vermiculite: Keep the soil moist. Germination takes one to three months. Once the seed sprouts, induce branching by cutting off the top 2 inches from the main stem when the plant is 6 inches tall, and then again when it reaches 2 to 3 feet tall. The avocado tree can stay in the 6- to 8-inch pot until it reaches 2 to 3 feet in height.
Repotting to a Larger Container
Avocados need to be repotted every two or three years, once the tree's roots fill the current container but before they start circling around inside the pot. Choose a new pot 1 or 2 inches bigger in diameter and depth. Good drainage is vital, especially in large or plastic pots that do not dry out quickly. When repotting, inspect the root system and prune off any broken or diseased roots.
Continue to move your avocado to larger pots as needed, but remember that if you summer your plant outside, it needs to be brought inside during the winter unless you live in a frost-free area. Very large containers are heavy and difficult to move, so plan for this in advance. The University of Arkansas suggests not leaving your trees outside too late, but instead moving them while outdoor nighttime temperatures are similar to your indoor temperatures. This minimizes the shock of the transition from outdoors to indoors.
Top Dressing Your Avocado Plant
Avocados can be kept in the same pot indefinitely by carefully removing the top 2 inches of soil from the container and replacing it with fresh soil every spring. However, once the tree's roots have filled the pot, root-pruning will be necessary to control the plant's growth.
Root-Pruning Your Avocado Plant
It's often best to root-prune container-grown trees over a two-year period. In the first year, knock the plant out of its container and loosen the soil around the roots with your fingers, then prune off 1 inch of the outer roots from half the rootball. Use fresh potting soil in the container when you replace the tree. Lightly prune the top growth to compensate for the root loss.
In the second year, follow the same procedure but prune the other side of the rootball. Root-pruning is best done in early spring, before the tree starts active growth for the year. Root-pruning can be repeated whenever the plant's roots fill the container again or when the plant reaches the maximum size desired.
Marie Roper began writing in 1987, preparing sales and training materials for Citadel, Inc. and then newsletters for Fullerton Garden Center. A trained horticulturist, she was a garden designer and adult-education teacher for the USDA Graduate School in Washington, D.C. Roper has a Bachelor of Arts in history from the University of Maryland.