ChatGPT can suggest plants and layout ideas for your garden, but it cannot generate a realistic redesign of your actual yard from a photo. As a planning assistant it works well: ask it for shade-tolerant shrubs for zone 6, a rough planting schedule, or pros and cons of gravel versus pavers, and the text answers are genuinely useful.
Image output is the weak spot. ChatGPT produces generic illustrations rather than editing your real space, so the dimensions, light, house, and existing trees in the picture are all invented. Most garden decisions hinge on how things look in your space, not a hypothetical one.
A sensible split is ChatGPT for research and a purpose-built visual tool for the design itself. See how the two approaches differ with ChatGPT landscape design done on your own photo.