1. Ferrous sulfate, also known as black alum, is recommended to be sealed and stored to prevent moisture. Once it is affected with moisture, it will gradually oxidize and become trivalent iron that is not easy to be absorbed by plants, and its efficacy will be greatly reduced.

2. It shall be constructed and equipped on site. Some flower friends make a large amount of alum solution at one time and use it repeatedly for a long time, which is often unscientific. Because over time, black alum will gradually oxidize into trivalent iron that is not easy to be absorbed.

3. The application amount should not be too large and the frequency should not be too frequent. According to years of experience, the pot soil mixed with ferrous sulfate should be 5g to 7g per pot, and 0.2% to 0.5% for irrigation or spraying. If the dosage is too large and the topdressing times are too frequent, it will cause plant poisoning, turn the root gray and black and rot, and affect the absorption of other nutrient elements due to its antagonistic effect.

4. Suitable water should be selected for manufacturing. Ferrous sulfate in calcareous alkaline water simply becomes the oxide deposition of ferric oxide, which is difficult to be used by plants. Try to use rain, snow water or cold boiled water. If alkaline water is used as a last resort, 1 g to 2 g of potassium dihydrogen phosphate should be added to every 10 liters of water to make it a slightly acidic "improved water". Adding 3% vinegar in alkaline water also has a good effect.

5. When adding ferrous sulfate to alkaline soil, it is necessary to apply appropriate potassium fertilizer (but not plant ash). Because potassium is conducive to the movement of iron in plants, it can improve the effectiveness of ferrous sulfate.

6. The application of ferrous sulfate solution to hydroponic flowers and trees should avoid sunlight. Sunlight shining on the nutrient solution containing iron will make iron deposit in the solution and reduce its effectiveness. Therefore, it is advisable to cover the container with black cloth (or black paper) or move it indoors to avoid light.

7. The mixed application of ferrous sulfate and rotten organic fertilizer solution has a very good effect. Due to the differentiation of organic matter, the product has a complexation effect on iron and can improve the solubility of iron.

8. Ammonia nitrogen fertilizer and elements that have antagonistic effect with iron should not be applied together. Ammonia nitrogen (such as ammonium sulfate, ammonia carbonate, ammonium phosphate and urea) can destroy the complex between organic matter and iron in soil and water, and oxidize divalent iron into trivalent iron that is not easy to be absorbed. Calcium, magnesium, manganese, copper and other elements have antagonistic effects on iron and can reduce the effectiveness of iron. Therefore, the dosage of these elements should be strictly restricted. When applying ferrous sulfate, try not to apply fertilizers containing these elements.