Dependent picklists - Controlling field not on the page layout

Dependent picklists are handled through Javascript on the page, so if the controlling field isn't available, there's no way to handle that functionality. You must be setting that controlling field some other way than through the UI, but I wonder about the usefulness of not being able to create a new record with a non-null controlling field anyway.

The only way I know of to control picklist values, without Visualforce, is through Record Types, which may or may not be a good solution for you.

If the use case is just updating field A based on Field B why not use a field update workflow and hide field B from the pagelayout??

please correct me if I missed something