Yes, AI can design a garden for free, but free tools usually limit you to a few low-resolution images, watermarks, or generic results. ChatGPT's free tier will suggest plants and rough layouts, and its image tools can sketch a garden scene, but the output is an illustration, not an accurate render of your actual yard.
Free is fine for inspiration. Collect ideas, compare styles, and rough out a plan before you spend anything.
The gap shows up when you want a realistic picture of your own garden. Purpose-built paid tools work from a photo, keep your home and layout intact, and render styles you can act on. You can see how that compares with a general chatbot on our ChatGPT landscape design page.