Plant Fertilizer Basics: Food for Thought

George and Becky Lohmiller
Food for Thought


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Fertilizer is made up of distinct elements in different blends, labeled with numbers like 5-10-10, 10-10-10, and 10-6-4. Here is some information to take the guess work out of fertilizer and to provide your plants with the best possible food!

Three Main Elements

There is valuable information in the labeled numbers: They indicate the amount of nitrogen, phosphorus, and potassium (standardized in that order) in the particular fertilizer blend. For example, 100-pound bag of 10-10-10 contains ten pounds of each element. The rest is filler, which gives it bulk and makes it easier to spread.

  • Nitrogen (N) is needed for leaf growth and is responsible for making plants greener. This is why most lawn fertilizers are high in nitrogen, with formulations like 24-4-12 or 20-2-6.
  • Phosphorus (P) is associated with root growth and fruit production. Tomatoes and root crops favor “snacks” of 5-10-10.
  • Potassium (K), also known as potash, helps the plant fight off diseases and keeps it vigorous. Plants deficient in potash may display stunted leaves and fruit and be extra sensitive to drought.

17 Essential Nutrients

  • Calcium, magnesium, and sulfur are needed in smaller amounts than N, P, and K.
  • Micro-nutrients: These are the 11 remaining nutrients essential to plant growth. Fortunately, they can be found in healthy organic soil and seldom need to be added in fertilizers.

Shopping for Fertilizer

Shopping for fertilizer can be confusing because plants have individual nutrient requirements.

  • Evergreens — holly, rhododendron, yew, and others — not only need high nitrogen to keep them green, but several trace elements as well. Evergreen food may have an analysis of 30-10-10, plus a dose of copper, molybdenum, and iron.
  • Flowering annuals, on the other hand, burst into bloom when nitrogen is held back. The tonic they need is 5-10-10.
  • Organic plant foods may not deliver the quick boost to plants that chemical fertilizers do but will feed them over a longer period.
  • Good-quality bonemeal worked into the soil around newly planted bulbs keeps them springing up for several years.

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