TIn Foil- its a common dispute over and over again,some say its ok,some say its bad, Thats why you should (always learn to understand YOUR plants),Just cuz it hurts one guys,it might now hurt yours..
Now it is more common to hear bad stuff of tin foil rather than good stuff..do some research..
and in my opn.its a matter of how much light you have with the tin foil...but again its just another opn.that i got from (learning my plants)..and I do agree with jerry,it makes hotspots from the light reflecting off the tin foil like lasers...thats why its called Hotspots..just a few brownish looking spots on only a couple leaves...
white reflects better than anything....its a common knowledge thing....
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as for covering your soil...sorry id have to disagree with that one,reason being....
that only works if your growing hydro..your roots are more subject to seeing light..with soil growing,once your roots are a inch or two in the soil...they are not seeing the light of day,inless you got worm holes in your soil..lol
and when you water your soil and then cover it up so no light gets in there,your soil is going to stay wetter longer,some may think that is a good thing,but it can lead to a ph problem in your soil,and fungus growing from your soil,from the over amount of moisture just sitting around. the light helps the soil dry up..which in regards makes the plant use more of the water,
if your soil was wet & dark how much is one plant going to be able to suck up? without getting root-rot? inless your running 100 degrees or something...