You imported your plants (or other blocks) into SketchUp from CAD, but they appear extremely small or far away.
SketchUp best practice is to limit the size of your model to about 1 square mile. You are likely working with a CAD drawing that covers an excessively large area, and your plants and/or blocks may be several miles (or several hundred or thousand miles) from the origin.
Fortunately, our SketchUp Connection will respect the current User Coordinate System (UCS) in CAD, giving you an easy method of setting a more usable origin. For more information on setting a UCS in CAD, see our Define a New UCS page.
So essentially, you'll most likely need to go back into CAD and create a UCS that allows your site design to stay within a square mile area at most. You can then export the drawing again using the SketchUp Connection and then import into SketchUp again.