The Cannabis Grow Bible
by Greg Green
Well…what can we say causes this..Hmm there are a number of things. If you followed H) right then you should not have this but we will explain it anyway. Lockout occurs when the plant can not get access to a nutrient or a group of nutrients. This could be caused by the absence of nutrients (a deficiency) or by a chemical reaction in the medium/solution that causes a toxic substance to block the roots, or causes a chemical reaction that creates another substance that changes the chemical properties of the other nutrients. As you can see this is really a very open subject matter. pH problems can lockout nutrients, your soil type can lockout nutrients, your water can even lockout nutrients. But these lockout causes are rare and more than likely something other than what cannabis needs has been added to the solution causing this reaction. When in doubt, transplant into fresh soil or a fresh hydroponics unit, depending on your grow method.