Feeding and Fertilizing Plants
Plants require nutrients, but fertilizer is not plant food in the same sense that food is for people. Plants manufacture sugars through photosynthesis and obtain mineral nutrients from the growing medium. Fertilizer is useful when nutrient supply is insufficient or when a particular crop and soil-management system calls for supplemental nutrients.
The Major Nutrients
Nitrogen is closely associated with leafy growth, phosphorus participates in energy transfer and reproductive processes, and potassium contributes to many aspects of plant regulation. Plants also require calcium, magnesium, sulfur, and several micronutrients.
Nutrients work together. Adding large amounts of one nutrient does not automatically correct a deficiency caused by another nutrient or by poor root conditions.
When Fertilizer Is Appropriate
Fertilization is most useful when supported by the crop's needs, soil conditions, or a soil test. Container plants can have different nutrient requirements because repeated watering can move soluble nutrients out of the limited growing medium.
Do not fertilize automatically every time a plant looks unhealthy. Poor growth can result from insufficient light, root damage, incorrect watering, temperature stress, pests, disease, or unsuitable soil.
Understanding Fertilizer Labels
Fertilizer labels identify the product's nutrient analysis and provide application instructions. The recommended rate, timing, placement, and frequency are important. More fertilizer is not necessarily better and can damage roots or contribute to nutrient runoff.
Record the product, rate, and date when making significant applications. This prevents accidental repetition and gives you a useful history when evaluating plant performance.
Organic and Synthetic Fertilizers
Organic fertilizers are derived from plant, animal, or mineral sources and can release nutrients at different rates. Synthetic fertilizers are manufactured to provide nutrients in specific concentrations and forms. Both can be useful when applied appropriately.
The important distinction for the gardener is not simply the label category but how the product behaves in the soil, how much nutrient it supplies, and whether that amount matches the crop's needs.
Avoiding Overfertilization
Excess nutrients can injure roots, create excessively lush growth, interfere with nutrient balance, and move into waterways. Store fertilizer securely and measure applications rather than estimating by eye.
A soil test is particularly valuable before making large corrective applications. Build fertility gradually through good soil management rather than trying to force growth with repeated fertilizer applications.
Practical Checklist
- Identify the reason for fertilizing before applying a product.
- Read the fertilizer analysis and directions.
- Use soil tests for major fertility decisions.
- Measure applications instead of estimating.
- Avoid using fertilizer as a substitute for fixing light, water, root, pest, or disease problems.
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