Its also a MYTH to not supply a good amount of Nitrogen during flowering. All Nitrogen is to a plant is Protein. Humans eat protein, and turn it into nitrogen. Plants skip this process. Nitrogen should be added in the same ratio as Phosphorus. Protein is the most important nutrient. Protein means of first importance. It makes no sense to limit protein during flip. Your plant will be growing the most its ever grown in both size, and flower production. Many hormones will be created as well as stigma growth, and trichome production. Weed should get an ever increasing amount of nutrients during most of flowering/ Nitrogen included. The main thing is the balance of nutrients. Blooming nutrients vs Veg nutrients IMHO are a just way to separate you, from your money. They should just have a good base nutrient structure during all phases of growth. In a 8 weeks flowering strain, and using chemical fertilizer, it may be beneficial to add Monopotassium Phosphate during weeks 3-5, along with a good base fertilizer. I use Hydro Garden Chem Gro 4-20-39-Calcium Nitrate 15.5-0-0, and Epsom Salts. Cut back on all nutrients the last 2 weeks of flowering. NO FLUSHING.
For organic I use Peruvian Seabird Guano, both high nitrogen-( 12-11-2 ), and high phosphorus formulas ( 0-11-0 ), Kelp, which I use as my Potassium source, Azomite, Dolomitic/Calcitic Lime, worm castings. At 20%, Seabird Guano is also high in calcium, and other trace elements as the seabirds eat fish, and the fish eat other fish, and kelp. I also make a tea from the guanos, and kelp, and use once every 2-3 weeks. Seabird guano is also very fast acting. For the kelp as a tea, I soak it in water for 3 days before use. You should also use air stone bubbelers, or mix it up several times a day. Or both. Kelp is a great source of Potassium, hormones, and trace minerals.