The Q&A Archives: What Does Plant Food Do?

Question: What does plant food do when plants are grown with it?

Answer: There's so much to tell about fertilizers! First of all you need to know a little about what plants need to grow--after all, that's why we apply fertilizers in the first place. Although plants make their own "food" through photosynthesis, they need certain nutrients to help them do this. Usually, these are found in the soil. The major plant nutrients are nitrogen, phosphorus, and potassium. Most fertilizers you see have an "NPK" rating, for example 5-10-10. This simply means the ratio of nitrogen (N) to phosphorus (P) to potassium (K--the chemical symbol for elemental potassium). Plants also need a variety of micronutrients--they are just as essential as the macronutrients, though plants need them in much smaller quantities. Plants can usually get these from the soil, but many "organic" fertilizers are made from materials like kelp (seaweed) and fish emulsion so they contain many trace minerals. Most "synthetic" fertilizers contain only N, P, and K as stated on their label. Some micronutrients are: boron, calcium, magnesium, manganese, and copper. The pH of the soil--how acid or how alkaline it is--affects how plants take up nutrients. Last but not least, even though the nutrients are present in the soil, if the soil is too acidic or alkaline these nutrients become "locked up" in complex molecules that plants can't use. That's why people apply lime (to raise pH) or sulfur (to lower pH) to their soils. Which pH is best depends on the preferences of the plants you are trying to grow, but the majority will manage with a pH near neutral. I hope this is helpful.

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