You mean to model hard and soft landscape elements as a landscape architect would, ultimately making design communication and construction documents.
Archicad is very useful when designing 3D landscape.
Archicad's strengths in landscape are the same as for building architecture - fast logical modeling and streamlined document production.
It can model slopes, contours and other features, inserting roadways and other hard elements with ease. It can also place plant elements at the correct altitude on irregular surfaces.
Archicad has some drawbacks that most modelers have when addressing the complexities of organic form.
If you want to model accurate 3D organic trees throughout your project, this will be nearly impossible because trees have so many polygons. To maintain computer speed, architects rely on photos of trees or simple translucent spheres to depict foliage.
There is an application called Onyx Tree Pro that makes botanically accurate trees, but they have many thousands of polygons that must be used sparingly.
There is also an Archicad add-on called "ArchiTerra" that simplifies many modeling tasks when creating the model.
Dwight Atkinson