Members of the Persea genus, avocado plants grown indoors from seed often have to be discarded after two or three years because they outgrow their space. If you grow them indoors from seed, they may take more than 20 years to bear avocados or they may not bear fruit at all. Avocado trees that grow outdoors from seed typically yield fruit in seven to 15 years. Whether you germinate an avocado seed in water or soil, it will typically sprout within two to three months.