Solving the pH Puzzle

Micro-Tech, Cal Mag Max 7-0-3, Nitro-30 SRN, "TKO" Phosphite, Arbor Care 15-8-4

Soil pH: everyone knows it's important for plant growth and health, but not everyone understands exactly what it is. Even fewer people understand how proper pH management can save them money.

Science 101

Defined as a logarithm of a hydrogen-ion concentration, pH is a significant factor in plant growth and health. Expressed on a scale of 0 (most acidic) to 14 (most alkaline), pH is neutral at 7.0.

In nature, soils tend to have a more limited range, from about 4 (which equals the acidity of orange juice) to about 9 (which equals the acidity of many soaps and shampoos). Soils in the arid Western U.S. tend to have alkaline ("sweet") soils, while soils in the rainy Eastern U.S. tend to have acidic ("sour") soils.

Influence on Plant Nutrient Uptake

Soil pH has a huge influence on the availability of nutrients necessary for plant growth. A soil may contain all the nutrients a plant needs, but unless the soil pH is in the correct range, the plant can't access the nutrients and will suffer severe deficiencies.

How can a plant be nutrient-starved in a sea of nutritional plenty? Plant roots absorb mineral nutrients only when nutrients are dissolved in water. If soil pH is too acid or too alkaline, the nutrients won’t fully dissolve and remain unavailable for plant uptake.

Take a look at the chart below. The thickness of each colored band indicates the percentage of each nutrient that is available at various pH levels. For example, nitrogen is almost 100 percent available for plant uptake in soils in the 6.0 to 8.0 pH range, but its availability tapers down on either side of that range. At 5.0 and 9.0 pH, nitrogen is only about 50 percent available. In contrast, phosphorus is almost 100% available in the much narrower soil pH range of 6.5 to 7.5. It becomes highly bound to the soil as the soil becomes acidic, and at a pH of 6 less than half the phosphorus in the soil can be utilized by plants.



Low pH levels cause excessive availability of iron and manganese, which can lead to toxicities. Conversely, high pH levels lead to deficiencies of P, Fe, B, Cu, Zn and Mo.

Balancing Your pH and Balancing Your Budget

Unless you know your soil pH, it is easy to over-apply ground fertilizers in an attempt to correct a nutrient problem. Oftentimes, the nutrient problem lies not in the amount of nutrient in the soil, but in having a soil pH that is too high or too low. What to do? Follow these three simple steps:

  1. Test your soil! For less than $50, you should be able to get a full soil analysis, including a soil pH score.
  2. With your test results in hand, study any nutrient deficiencies. For nutrients such as Calcium and Boron that are immobile in soil, apply a foliar spray (such as Micro Tech or Cal Mag Max 7-0-3) that includes the needed micro. Plants readily absorb nutrients through leaves, so foliar feeding by-passes any soil pH problems.
  3. For deficiencies of macro and micro nutrients that are mobile in soil (e.g., the vast majority of nutrients), alter the soil pH to make the existing soil nutrients more available or apply foliar sprays to immediately correct the problem. Quick-acting foliar sprays include Nitro-30 SRN 30-0-0, "TKO" Phosphite, Arbor Care 15-8-4, and an array of other targeted products.

Unless you know your soil pH, it is easy to over-apply ground fertilizers in an attempt to correct a nutrient problem. Oftentimes, the nutrient problem lies not in the amount of nutrient in the soil, but in having a soil pH that is too high or too low. What to do? Follow these three simple steps: