What nutrients do you use to get the best root gro...

There's no real wrong answer here , lot's of companies offer a wide variety of root boosting agents . Personally I like Advanced Nutrients Voodoo Juice and Piranha . These 2 products used in combination allow for multiple benefits to your plants but the main one is root boosting . Study's have shown that these 2 used in combination in the first 4 weeks of your plants life will boost your root production by nearly 800% with some other great benefits as well , but just the root boosting abilities alone make the products worth it . You don't have to use them in combination to get great results either . One or the other will do just fine or if you can use both then I highly suggest doing that . First 4 weeks of your plants life then first 2 weeks of flower and you will see quite the difference , your root mass will be quite robust and what I like to call muscle-y haha . These are just some of the products out on the market that will do what your looking for . There are tons and tons and tons on the market so do your research before you buy one this way you know what your getting. Remember that bigger the root bigger the fruit in our case flowers :D . I hope this information serves you well on your quest for knowledge ! Happy Growing !