In my experience most MLA programs admit students with a wide degree of backgrounds both academically and professionally. I got my masters degree and none of my classmates had a bachelors degree in landscape architecture. Some had architecture degrees though but most were interested in the field and chose to pursue a masters in it.
during your masters education work hard on learning the skills you will need to be productive in the workplace. And use your psych background to help inform your understanding of LA.
Landscape architecture is not a field in which there is one way to do things. Collaborate with others and learn as much as you can.
I entered a career discovery program to learn more about the design field and found it to be extremely helpful.
Good luck.
