The first way is similar to making a balcony: draw a room with the size of your garden and set either the wall thickness or the height as 0 (select the wall and click on the i-button).
In this way, when you view your plan in 3D, you won't see the walls but they will be still visible in the 2D view. The next step is to click on the i-button of the floor and choose the grass as your pattern.
Here is important to point out that if your garden goes around the whole house, then your plan at this point will look like this:
The reason for this is that your house is recognised by our platform as a 'room inside a room' and therefore sets the same floor pattern for the whole plan. In order to avoid this, you just need to draw an additional wall:
Add fences, plants and outdoor furniture from the catalogs to give your garden a complete look:
The second option is a little bit different.
In the 3D view the ground outside the floor plan anyway looks green - thus, instead of drawing a room, you can use the Ruler to set the size of your garden and put fences along the garden's borders.
Your complete garden will look something like this in 2D and 3D view: