After looking for qualifying words in the claim, the next step is to determine what the writer considers to be the situations in which her claim doesn't apply. In other words, it is necessary to identify any exceptions she makes to her claim. In her argument, although she does not mention explicitly any exceptional situations, her claim implies one.
If we look at the writer's claim in paragraph 2, "It is time for us to rethink our landscaping practices," the first thing we should ask is "Who does she refer to when she uses the word `us'?" Clearly, this writer is addressing an audience like herself: homeowners in the West (in Ft. Collins, Colorado perhaps) who are interested in landscaping. Then if we look at the introductory paragraph of the essay, we see that she has described two landscaping situations: one in her home state of Ohio, and one in Fort Collins, Colorado, where she now lives. From all of this, we can assume that the writer intends for her argument to apply primarily to lawns in the West, and that (by implication) she excludes from her argument lawns in other parts of the country, where conditions are different.