NEW YORK CITY PARK:
Some parks in New York City, such as Central Park, Madison Square Park, and Prospect Park, are property of the city and run by the Department of Parks & Recreation (and are sometimes also managed by a separate group such as a conservancy or alliance). For these parks a permit is only needed if you’ll have more than twenty people or if you’d like to reserve a specific area within the park. These permits cost $25 and require a minimum of 30 days notice. One exception is Conservatory Gardens in Central Park, where they require a $400 ceremony permit, with an additional $100 permit for photography. Another exception is Brooklyn Bridge Park where there is a $400 non-refundable site fee for all wedding ceremonies, in addition to the $25 non-refundable application fee. It's important to research the requirements for a park before you make your plans, invite your guests, etc.
NEW YORK STATE PARK:
A few parks in the city are actually run by the state and generally have more strict permitting rules, although they vary park to park. These parks include Gantry Plaza State Park, East River State Park, and Hudson River Park, among others. Most will require a photography permit, and some will require an event permit for the ceremony itself.
Lower Manhattan Venues
Information specific to Central Park, including restrictions and suggested areas of the park suitable for ceremonies.
On a budget? Many local convenience stores sell flowers and can put together a simple bridal bouquet very quickly. Some stores even have a few ready-made on hand each day.
All the information you'll need to apply for a marriage license at the New York City Clerk's office.
Lots of information for all boroughs on the requirements for having a ceremony in any of New York City's beautiful parks.