Just got back from the Cincinnati Zoo and Botanical Gardens. If you ever have a chance you should stop by whether in the Spring or Winter or any season. Winter is amazing because they decorate the entire zoo with Christmas lights, but in the Spring you can view the 100, 000 tulips that were planted by volunteers last Fall.
Also you may want to click here to read about the zoo's trial gardens for annuals and their picks for 2012 annuals.
Further more if you are curious about what they do with all of their poo, Marvin's Organic Gardens picks it up for composting and sale to the public. Marvin's is known as Number 1 in Number 2 according to this video