Remember that during the flowering stage, plants need a lot of nutrients such as phosphorus, potassium and of course magnesium to develop large flowers and the original smells and flavors naturally present in the plant. Here's a good read !
Magnesium during the flowering stage of cannabis plants
Many of the deficiencies that we can observe during the flowering period are given due to an excess with the bloom ferts Most ferts for this phase contain high amounts of phosphorus and potassium: it should be said that potassium and calcium are two nutrients that can cause magnesium lock-out when added in excess.
Usually, this lock-out occurs during the first weeks of flowering - when the plant is creating buds - approximately during the third-sixth week of flowering, depending on whether it’s an Indica or Sativa strain. During these weeks, and if we use too much fertilizer, we'll cause an excess of potassium (K) that will block the absorption of magnesium (Mg). To solve this nutrient imbalance, flush the roots to lower the nutrient excess in the substrate so that the plant can absorb Mg again.
It’s also necessary to emphasize that the deficiency often appears because the substrate doesn’t have enough Magnesium; in these cases, we should provide our plants with magnesium during the above-mentioned weeks, either directly in the soil - by adding limestone dolomite - or through irrigations, using a Mg supplement in he nutrient solution and via foliar with a Ph level of 7.1. You'll notice a quick recovery of marijuana plants. Happy growin