Once picked, avocados ripen in one to two weeks (depending on the cultivar) at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas).
Some supermarkets sell ripened avocados which have been treated with synthetic ethylene to hasten ripening.
This limitation, added to the long juvenile period, makes the species difficult to breed.
Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next.
The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates.
Most cultivars are propagated by grafting, having originated from random seedling plants or minor mutations derived from cultivars.
Modern breeding programs tend to use isolation plots where the chances of cross-pollination are reduced.
Several cold-hardy varieties are planted in the region of Gainesville, Florida, which survive temperatures as low as −6.5 °C (20 °F) with only minor leaf damage.