Are you growing in soil or hydro? If you are growin soil you should be fine. Hydro should be fine if you have everything dialed in. A 2 or 3 day trip shouldn't be an issue if you water your soil the same day or the day before you leave. Just make sure you have everything setup they way you want it. Its all about how you feel about your own setup. If you dont trust it than dont do it. But ill tell you 3 weeks flower isnt going to be a very good yield or smoke. Not to mention they need to be flushed and cured before smoke. Its all up to you.