A quicker way to do it would be to package the lot as is, then use clean installer to install only the lot segment to a game that doesn't have the landscaping items installed.
I haven't tested this, but I figure it's worth a try!
I think the lot segment would include the maxis originals for custom items, and since some custom landscaping items are made from an unexpected original, you might end up with a rather wierd looking garden, and still have to remove those objects.