In my opinion, I don’t think you necessarily need to demonstrate landscape relevant projects. Landscape is a generalist discipline, we must account for a broad spectrum of information. So having a different background is what makes you a unique candidate. You just need to enhance this unique perspective and demonstrate how it could inform your thinking in the landscape design process. While well executed graphics are important, I think more importantly is that you demonstrate your design thought process.
Maybe take some masters level courses. Read as much as you can about the LA field. Best of luck!
