Both of those trees should be fine outdoors in your zone. They're quite hardy.

Josh

Agree with Josh...I would be more concerned about drying winds that could be stronger on some balconies. Obviously, it depends - is the balcony recessed? It may not be that windy where you live.

I had both of these plants in containers for few years without any additional protection - they were on ground in garden. Ginko was planted in ground after about 5yrs in pot (started from seed) and in few years grew into a huge tree :) Your zone is warmer than mine.

And they need some moisture in winter - but you probably know that since you overwintered them already.

thanks for the responses. So no mulching for either? No concern about roots/cells making up roots freezing in their pots?

The roots of many plants can be damaged if exposed to temperatures in the low 20's for any length of time. The larger the container, the less this becomes an issue as it takes time for the soil mass surrounding the root system to reach those very low temps. If you experience a cold snap that brings you down into that temperature range for more than just a day or two, you can wrap the pots in bubble wrap until it warms up. Otherwise, in your zone, you won't need to do much else.