Hiring a designer is worth the cost when the work is structural or permanent, like retaining walls, regrading, drainage fixes, or a full yard build. Expect $50 to $150 per hour, or $800 to $3,000 for a complete plan; many design-build firms credit the design fee against the project if you hire them for construction.
It is harder to justify for cosmetic changes. On a new bed, mulch, and a few shrubs, the fee can rival the cost of the materials themselves.
Either way, you decide faster with a picture. Generating AI concepts from a photo of your yard tells you what you actually like before anyone bills an hour; OutdoorBrite's plans cover a month of designs for less than most designers charge per hour.