I overwintered my young chilean guava outside in seattle and it survived the cold november (20's) we had last year. Likely by fall, they should be old enough to survive zone 8-9 if it doesn't get especially cold - just be prepared to protect them if it freezes any colder than that. BTW - my hardy cuttings (rooted and unrooted) stay out all winter in the cutting box with no protection.

Arthur Lee gives a great summary on this fruit plant that makes you really want to grow it. Anyway I enjoy the strawberry and pineapple flavored ones and thought I would give the pineapple ones a try too. Best benefit is it does grow true from seed. Just use fresh and read up on how to propagate (3 weeks) and you should be smooth sailing!

Here is a link that might be useful: Black Guava