1. Ferrous sulfate, also known as jarosite, is recommended to be sealed to prevent moisture. Once it gets damp, it will gradually oxidize and become trivalent iron which is not easily absorbed by plants, and its efficacy will be greatly reduced.

2. It should be applied on the spot. Some flower friends do a large number of alum solution at one time, long-term repeated use, which is often unscientific. As time goes on, the alum will gradually oxidize into trivalent iron which is not easy to be absorbed.

3. The amount of application should not be too large and the frequency should not be too frequent. According to many years of experience, it is appropriate to add 5 g to 7 g ferrous sulfate in each pot, and 0.2% to 0.5% for irrigation or spraying. If the dosage is too large and the times of topdressing are too frequent, the plants will be poisoned, the roots will turn gray and black and rot, and the absorption of other nutrients will be affected because of its antagonistic effect.

4. Ferrous sulfate in calcareous alkaline water is very simple to become trivalent iron oxide deposition, which is difficult to be used by plants. Try to use rain, snow or cold water. If you have to use alkaline water to make it, you should add 1 g to 2 G potassium dihydrogen phosphate to every 10 liters of water to make it a slightly acidic "improved water". Adding 3% vinegar in alkaline water also has better effect.

5. When ferrous sulfate is mixed in alkaline soil, appropriate potassium fertilizer (but not plant ash) should be applied. Because potassium is conducive to the movement of iron in plants, the effectiveness of ferrous sulfate can be improved.

6. The application of ferrous sulfate solution to hydroponic plants 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 into a dark place indoors.

7. The effect of ferrous sulfate mixed with decomposed organic fertilizer solution is very good. Due to the differentiation of organic matter products, ferrous sulfate has complexing effect on iron and can improve the solubility of iron.

8. Ammonia nitrogen (such as ammonium sulfate, ammonium carbonate, ammonium phosphate and urea, etc.) can destroy the complex of organic matter and iron in soil and water, and oxidize divalent iron into trivalent iron which is not easy to be absorbed. Calcium, magnesium, manganese, copper and other elements have antagonistic effect on iron, which can reduce the effectiveness of iron. Therefore, the amount of these elements should be strictly restricted, and the fertilizer containing these elements should not be used when ferrous sulfate is applied.