A nutrient deficiency is not immediately visible in plants , because they only show it after a few weeks. Therefore, you have to react quickly at the first sign. Depending on how the leaves or the whole plant behave, one can also infer certain defects.
Leaves are pale in color
If the leaves are pale in color and the plants do not flower, then there is a nitrogen deficiency. This can only be fixed by mixing some fertilizer into the irrigation water.
Leaves are blotchy
If the leaves are not only lighter in color but also blotchy, this is a sign of magnesium deficiency. Here you need a fertilizer that contains trace elements.
Leaves are light yellow
If the leaves are light yellow in color but the veins remain green, this indicates an acute iron deficiency. This can only be fixed with a special iron fertilizer. Petunias in particular often suffer from this.
Brown leaf edges
Brown leaf edges indicate potassium deficiency. If you use a high-quality fertilizer regularly, this should not happen in the first place, because all the important nutrients are contained here. After fertilizing, it may take a few weeks for the plant to recover.