if my plants start to pre flower or flower can grow hurt them

If you mean..can grow fertilizers or amendments hurt them, now that they are flowering - the answer is No. Mary takes in what she needs, when she needs it. In nature NPK ratio's are not perfect & Mary grows just fine.
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By following Grow / Flowering Feeding Schedules - we are just tweaking Mary - like NASCAR Racers tweak their cars for optimium performance. In their line of work, being one thousandth of a second faster makes them "The Champion".
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As long as you don't overfeed Mary (unneccessary high doses - following the more is better line) she will be fine. In the end, do all those High End Ferts really make a difference ? Well, I will not lie - Yes they do - a very tiny, tiny one - like maybe, a few extra grams per plant. Not worth the price in my book. I'm Frugal.....
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However you decide to grow - Organic or Chem - Start low, build as you go. A little higher N for growing & a little higher P for flowering. Tried & True Formula's that work. I don't subscribe to the no N during flowering - I have never seen it truly proven to make substancial differences.
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The Big Fert Companies - selling you two or three part ferts - are making two or three times the money from you. The truth is Peter's (a chem fert) 20-20-20, cut down to a 5-5-5 or 10-10-10 NPK grows almost as good weed - for a lot less money.
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Now, I prefer Organics - but I will not lie to you and say (chem ferts) are all bad. They are not. At the end of the day NPK is NPK. I just prefer worm castings, bunny rabbit manure & bat guano - the don't require extra engery to produce, bottle, ship and market - like chem ferts.
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Nothing is all good or all bad. I like Organics others do not - it is for each of us to decide what works for us.
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Hope this Helps....
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