Understanding Soil Nutrients: The Macronutrients Nitrogen, Phosphorus and Potassium (N, P and K)

How much do you know about the soil nutrients that your garden vegetables need to survive and thrive? Do you know what macronutrients and micronutrients are in your garden soil? Can you tell what nutrients your plants need just by looking at them? If not, don't fret — here are the basics.

All Nature's Soil Nutrients, Big and Small

To grow as well as they can and grow as much produce as possible, garden vegetables (and herbs!) need over a dozen different nutrients in the soil in which they grow.  Based on how much of a given nutrient most plants need to flourish, these soil nutrients are known as macronutrients or micronutrients. One type (the macronutrients) is needed in relatively large amounts, while the other (micronutrients) is often needed in small (if not trace) amounts.

Soil Nutrients NPKThe micronutrients (which most novice gardeners don't even know about) include boron, copper, manganese, molybdenum and zinc. These soil elements are often already present in soil, since most plants don't use them heavily.

Then there are the big garden guns. Unlike the micronutrients, soil nutrients like nitrogen, phosphorus and potassium (also often just referred to as N, P and K) are needed in relatively large amounts. Depending on what you're growing, these vital soil elements may be used up and require supplementing during or after your gardening year, and it is these soil and plant nutrients that most folks are concerned with when they fertilize, spread compost and amend their soil.

It's important to remember that while only needed in small amounts, micronutrients are no less important than the macronutrients: a serious deficiency in any one of these soil elements can still damage your garden veggies.

What Different Macro Soil Nutrients Do

Just like different nutrients do different things in your body, various soil elements serve different functions in plant bodies. For instance:

  • Nitrogen (N) gives plants their deep green coloring, increases leaf and stem growth, and stimulates fast, early growth.
     
  • Phosphorus (P) is vital to seed formation, stimulates early formation of roots, promotes vigorous root growth, and helps fall-seeded grains and grasses.
     
  • Potassium (K) improves the quality of crop yields, increases plant health and disease resistance, and stimulates the production of strong, healthy stalks.

Signs of Soil Nutrient Deficiency and Excess

As living entities that react to their environments, it should come as no surprise that plants exhibit physical symptoms when the soil in which they're growing is deficient in the key soil nutrients they need to grow. And, while soil tests and soil nutrient analysis are really the only way to be positive what soil elements your garden is short on, side-eying your plants and vegetables can give you some pretty good clues.

Common symptoms of soil element deficiencies:

  • Light green or yellow leaves (nitrogen deficiency)
  • Red or purple leaves (phosphorus deficiency)
  • Thin skin and small fruit (potassium deficiency)
  • Stunted growth (nitrogen deficiency)
  • Weak stems and roots (potassium deficiency)
  • Spotted or curled older leaves (potassium deficiency)

Common symptoms of excess soil nutrients:

  • Dark, excessive growth (excess nitrogen)
  • Brown leaf tips (excess potassium)
  • Fast growth with weak, spindly stems (excess nitrogen)
  • More leaves and stems produces than edible fruits, flowers and roots (excess nitrogen)

As the list above should show you, it's entirely possible to hurt your plants by over-fertilizing with certain soil nutrients. And that's not the only danger. Even those soil elements that are not likely to harm your crops when in excess (like phosphorus), can still pollute local surface and ground water. The point? Don't try to outsmart your soil by over-fertilizing. Just save your money and your time and fertilize when your plants actually need it.

Ready for more information about your garden soil? Here a few more articles you may want to check out: Natural Ways to Test Soil Quality and Understanding Your Garden Soil. And don't forget to check out my Gardening Guides page for all sorts of smart gardening info like recommended pH levels, planting times and more.

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