In any industry there can exist areas of specialization and there are designers that focus on water features, hardscaping, swimming pools, native plantings, rain gardens, sustainable landscapes, etc., etc. but the greatest employment/client opportunities will be available to a designer that is versatile in all aspects of landscape design. Get a broadbased educational background and as much practical experience in all aspects of design and installation as you can manage first, then figure out what aspect you like the best or what specific niche you can fill that seems lacking in your location and focus on that. But get it ALL in hand and under your belt first :-)

I agree. In order to specialize, you already have to be well known and skilled in broader areas.

It is like screening rocks. If you start by putting them through big screens and work to finer screens a lot lands in the bootom. If you start with the fine screen, very little gets through because all the holes get clogged.