Actually you don't want to fully cut out the Nitrogen ferts for the first half of flowering. The plant still uses the nitrogen for growth. It needs to grow another 30-50% in size, so it will still need nitrogen supplied, but not as much. It will need more concentrations of Phosphorus and Potassium for flowering, but it is still producing leaves and stem growth, not just buds. In the last few weeks you can cut it out and the plant will use the remaining nitrogen in the soil and lower leaves up to harvest. Actually tomato plants use the same fertilizers as cannabis. Even Ed Rosenthal has recommended Miracle Grow tomato food in his books, even though it is a chemical fert.