Wonderful Pomegranate

Will pomegranates ripen outside in Washington DC

The may ripen. However, they will not withstand the winter temperatures. Consider planting in a container and bringing the plant inside to overwinter. 

Can I grow Pomegranates in FL, just north of Miami? How many years from planting will it take to flower/fruit?

Yes, with some caveats. Florida is not an ideal environment for pomegranate. The things to consider are: they cannot tolerate wet soils, need regular compost application, and early on will require some winter protection. If they establish well, expect 5-7 years until maturity and fruiting. 

I live in N.E. Washington. We have very hot summers but also a get very cold. Will pomegranates survive?

Good question! Pomegranates are hardy to zone 7, which is down to roughly 0.0 degrees. Many parts of Eastern WA are colder than that, but with extra winter protection you may be able to pull it off. We cannot guarantree survival however.

what are the chill hours required for this, if any?

200+ chilling hours. To be clear, all plants have chilling hour requirements, but some plants like pomegranate are so low it doesn't matter in the United States.

If I were going to try to grow a pomegranate in Chehalis, what variety would you suggest?

Any will grow fine in Chehalis, but outside of a greenhouse they are unlikely to fully ripen fruit.