Trace Minerals for Healthier Plants and Soils

by Don Trotter

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Hello fellow Earthlings, and welcome to the last of our series on minerals for your garden greenery. In this discussion we'll be touching on a group of minerals that our plants use in very small amounts. These minerals are commonly referred to as "trace or micro" nutrients. Manganese, Copper, Boron, Molybdenum, and Chlorine are our topics this time. So let's stroll over to a periodic table of the elements for some further learning on the subject of plant and soil nutrition.


Manganese is used by plants as the positively charged manganese cation. It is an activator for many enzymes in plant growth processes, and assists iron in the formation of chlorophyll during photosynthesis. Yet high concentrations of manganese may actually suppress iron uptake in plants.

Manganese is commonly applied along with zinc and can be applied to foliage in dilute liquid applications. Citrus and other fruit tree crops are frequently treated with supplemental manganese in the form of manganese sulfate. Manganese supplementation has no commonly recognized requirements and is normally only applied to plants after accurate diagnosis of a deficiency of this mineral. Deficiencies of manganese commonly appear as:

  • Interveinal discoloring of foliage with veins appearing deeper green. Discoloration is not as pronounced as iron chlorosis and is often difficult to detect.
  • Grey specks and interveinal white streaks on grasses


Copper is the mineral that makes certain types of fruit sweet. It is taken up by plants in two forms of positively charged cations and appears to play a role in the formation of vitamin A in plants. Copper is also and important activator of several plant growth enzymes.

Copper supplementation is rarely needed and the native supply in many soils is adequate to support plant growth. Highly organic soils and some sandy soils have shown a lack of copper. This mineral is toxic in small amounts and care should be used when determining a need for copper. Application of copper should be done with care. Copper sulfate is the most common form of copper supplementation given to soils lacking this mineral.

Copper is also a very useful fungicide and is used by many natural gardeners as a dormant spray to prevent diseases from entering plants. It is also used to fight off certain fungal diseases that have already appeared on plants. Cars and trucks entering into many of the avocado groves in California pass through tire dips of copper to prevent the spread of certain rather destructive diseases that attack this valuable fruit crop.

When checking if your soils are deficient in copper, it is a good idea to have a professional soil and plant analysis laboratory to determine whether supplementation is required. Symptoms of a copper deficiency in plants include:

  • Stunted growth
  • Death of new growth
  • Off color and poor pigmentation of leaves
  • Wilting and death of leaf tips


Boron regulates the metabolism of carbohydrates in plants. Boron is non-mobile in plants (much like calcium) meaning that a continuous supply is necessary at growing points. Boron is taken up by plants as the negatively charged borate anion. It is known to assist in the differentiation of particular types of stem tissue known as "meristem" tissue.

Boron is often present in toxic amounts in certain arid and semi arid soils. It is a very good idea to have your soil professionally analyzed before even thinking about adding supplemental boron to your soil. This mineral is commonly found to be deficient in areas of higher rainfall or where summer rains commonly fall. Boron is supplemented to deficient soils in the form of boric acids or other compounds.

Boric acid is also a known way to rid your garden of certain pests like ants. These uses for boron will be discussed further in our discussion on natural pest control in the garden. Deficiencies of boron appear as:

  • Thickened, curled, wilted and chlorotic foliage
  • Death of new and terminal growth causing what is referred to as a "witches'-broom" effect
  • Over development of lateral or side growth after terminal growth has died
  • Soft or dead spots on potatoes or other tubers and bulbs
  • Suppressed flowering or improper pollination of flowers


Molybdenum is used by plants in the form of the negatively charged molybdate anion. Plants require it so that they may utilize nitrogen. Your plants are unable to transform nitrogen into amino acids without molybdenum being present. Legumes and other nitrogen fixing plants also cannot fix nitrogen from the atmosphere symbiotically without molybdenum.

Molybdenum is rarely deficient and is normally only required in ounces per acre when supplementation is necessary. So it is safe to say that this important micronutrient is only required by plants in small amounts to be effective. The most common symptom of a deficiency in molybdenum is stunting of plants and an overall lack of vigor. When plants are deficient in molybdenum they often look like they need nitrogen. This is due to the key role molybdenum plays in the utilization of nitrogen by your plants.


Chlorine is often more available to plants than is healthy. It is required in photosynthetic reactions in plants and is taken up by them in the form of the negatively charged chloride anion.

Chlorine supplementation is almost never done. This nutrient is universally present in nature and is almost too available due to the chlorine in the domestic water supply to suppress bacterial growth. Since this nutrient is so widely present we won't be suggesting any of the symptoms of deficiency because I don't think it is wise for you to consider supplementation of chlorine under any circumstances. It is good to know that plants use it because otherwise there would be way too much of this stuff around even if our clothes were whiter.

As a footnote to this discussion on soil minerals, we should definitely touch on the importance of a balance for plant nutrients in soils. It is critical that a balance of plant nutrients be present in soils because an abundance of one can create a scenario of reduced uptake of another. Maintaining a balance of nutrients in your soil is an important objective of proper soil management. Judicious use of fertilizers and being mindful of soil pH is critical to ensuring the vigor and health of your garden. Next time we'll be discussing lawn care during the warm months of the year. See you in the Garden!

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Check out Donald Trotter's books Natural Gardening A-Z, The Complete Natural Gardener and Rose Gardening A-Z at

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