Final answer:
The sentences 'We planted flowers.' and 'We pull weeds.' are not a run-on when properly punctuated with periods. If combined without proper punctuation, they would be a run-on sentence.
Step-by-step explanation:
The sentence structure you've provided consists of two separate sentences: 'We planted flowers.' and 'We pull weeds.' These sentences are not run-on since they are properly punctuated with periods. However, if the intention was to combine them into a single sentence without proper punctuation, it would then be considered a run-on sentence. To avoid a run-on, the sentences must be separated by a period, a semicolon, or connected with a coordinating conjunction or a subordinating conjunction.