Guava, Psidium L., is a genus of tropical shrubs and small trees mostly native to the Americas and Asia, but they have been spread throughout the tropics and subtropics by trade and even ocean currents, but some are considered invasive in places such as Florida and Hawaii. The most common species is the apple guave, P. guajava L., since it is the one most used for fruit. The strawberry guava, P.cattleianum Sabine, is the next most import, while the pineapple guava is now classified in a monotypic genus as Feijoa sellowiana O. Berg., interestingly it is reported hardy in zone 8 but does not produce fruit due to flower bud damage that occurs at 16oF.
I have grown apple guavas from seed. They are apparently hardy into zone 9 considering where they have escaped in Florida. I know Katrina transplants to northeast Alabama that grew guavas in Louisiana. About the only requirement to get the seed to germinate is for the soil to be warm. I tested the cold hardiness of some of the seedling and they apparently didn't survive temperatures much below 30oF. Apparently guavas in Louisiana were either in protected locations whether it be near a structure or surrounded by lots of warm water, or were pineapple guavas instead.
