Landscape architects cost more and therefore tend to be engaged for more highfalutin' stuff than backyard layouts. But anyone can call themselves a landscape designer, there is not the same level of certification required to use the title.

If you find a landscape designer with a portfolio and/or references from other customers that look good then you don't need to pay the thousands more a landscape architect could cost for the same work. It depends on what you feel you need. Somebody who is a landscape architect might have a style or ideas that are perfect for you. If they want the job and you have the budget, that could be the way to go.

A landscape architect is a landscape designer with a professional degree and a professional license. That said, landscape design is a diverse field with many people specializing in very different areas.

I would pay a lot less attention to what degrees or licenses a person has (as long as they have what they need to do the job legally) and a lot more attention to how well they do what you are looking to have done.

Portfolio, personality, punctuality, price, and professionalism should be the priorities.