Is make plants grow well proper grammar?

No, "Make plants grow well" is not grammatically incorrect, but it's not a complete sentence. It's a phrase or a command. To be a proper sentence, you need a subject and a verb in a complete thought. Here are some ways to make it a sentence:

* "How do I make plants grow well?" (Question)

* "I want to make plants grow well." (Statement)

* "Making plants grow well requires effort." (Statement)

* "Make sure to make plants grow well." (Command)

The grammar itself ("make plants grow well") is fine within the context of a complete sentence.