Open space and planting count toward site coverage and zoning compliance just like the buildings do, so they need to be on the plan, not just implied. The Landscape tool shortcuts to all of the Landscape and Tree Usages in your project template. In the drawing toolbar, this button's icon looks like two trees.
If your project template doesn't have the usage you need, check the Marketplace: open the Content Library (from the main menu, or the + on any panel tab), click the Marketplace tab, then choose Usages.
What is a Landscape Use?
Landscape usages count toward open space and site coverage. Landscape type properties: Height, Stack Order, and cost properties (hard cost, soft cost, maintenance cost).
Draw landscape
Click the Landscape tool in the drawing toolbar.
Select a landscape usage from the dropdown.
Choose a shape in the shape picker: Rectangle or Polygon. Drawing starts as a rectangle.
Landscape can be placed on the roof of a building by turning on Stack: Always in the properties palette.
Trees
Tree properties: canopy radius, and cost properties.
Click the Landscape tool in the drawing toolbar.
Select a tree usage from the dropdown.
Click on the map to place the tree as a point.
Change its scale and rotation in the properties palette, or upload a new 3D model to change its appearance.