When to adjust marijuana fertilizer to flowering formula



At what point should I shift the fertilizer to the flowering formula: when the flowers start to show or when I switch the lights back?



Hi Tony,

The right time to change the fertilizer really depends on the method of growth. If you’re growing marijuana in soil outside, the fertilizer needs to be shifted when the plants are in the transition between vegetative and glowering. Every variety is different because they each have different critical dark periods that foment flowering.

If you’re growing marijuana inside, then the time to change is also dependent on the method of cultivation. Plants growing in soil or soilless mixes should have their formulas changed when the lights start to be shut off. This is because they have a large amount of residual nutrients like nitrogen which is vital for the beginning parts of flowering. Switching to high phosphorus or high potassium formulas allows you to just make use of the residual nitrogen. The nitrogen is used up by the end of flowering and the phosphorus and potassium can help produce a better formula.
In hydroponic systems, there is no residual nutrient quantity. Thus, the marijuana plants need to receive diet of high-nitrogen at the beginning of the flowering period. This is ideal for growing tissue (and the subsequent flowers). It’s somewhat common for flowering formulas to have a very low nitrogen content. Look at the label. If the flowering formula doesn’t have around 1/3 of the nitrogen as phosphorus, you should mix your flowering formula with the vegetative fertilizer for the first 2/3 of the flowering period. When marijuana doesn’t have any nitrogen to work with, it will transport the nitrogen from within its lower leaves to the new growth. This causes the lower leaves to die. Nitrogen only needs to be lowered at the end of the flowering period.