Hi! my plants are in the flowering stage and i have 2 diferent fertilizers. i want to know which one is better.
one has a npk of 4-8-4 and the other one is 7-28-18.
Those are percentages by weight. They're useful when comparing prices of different fertilizers (their relative value. Their strength. A fertilizer that is 8-16-8 gives you twice the NPK as 4-8-4. If they cost they same, the former would be the better value.).
But, for comparing the way you are, it's better to think of NPK as a ratio. Their balance. What you have is NPK ratios 1-2-1 and 1-4-2.6.
I'd go with the 1-2-1 in flower. Some people say all purpose 1-1-1 is suitable for all stages of cannabis life. Others say 3-1-2 is good in veg, 1-3-2 in flower. Others point to Advanced Nutrients use of PK ratio 1-2 throughout the grow, varying only the N from 3 (veg) to 0 (late flower).
So, 1-2-1 isn't too far from those ratios. You could mix the two fertilizers to get something closer to 1-3-2. I do this with Grow More Sea Grow (all purpose and Flower & Bloom).
I made a spreadsheet here (<<link) to see the resulting NPK ratio of mixing products. For example, you have to take into account any calmag product you use because they can contribute significant N.
