More Minerals for Healthier Gardens

by Don Trotter

Hello fellow Earthlings and welcome back to our interminable discussion on minerals that your plants use in order to grow healthier and happier. The minerals of the day are Magnesium, Iron, and Zinc, so let's take a walk in the garden and take a look at our soils and our plants to check if our gardens need a boost.


Magnesium is taken up by plants in the form of the positively charged magnesium cation. Cell division cannot take place without magnesium being present and magnesium serves as an activator for several plant enzymes required in the growth process. Magnesium is highly mobile in plants and can be moved from older to younger tissue rapidly in times of deficiency.

Magnesium can be supplied to plants from mineral sources such as dolomite lime, Epsom salts (magnesium sulfate), and Sul-Po-Mag (sulfate of potash magnesia). It is often applied to rose gardens to stimulate the growth of new canes. In western soils where rainfall is low, an abundance of magnesium can keep soils tight and impermeable to water penetration. The addition of calcium to soils high in magnesium will open them up to better water and air infiltration and improve percolation. The calcium magnesium dynamic in soils was studied and theorized by Professor William Allbrecht early in the twentieth century. He theorized that 5 to 7parts calcium to one part magnesium improved plant growth and soil tilth while enhancing plant uptake of other essential minerals present in soils.

Signs of a magnesium deficiency in plants often appears as:

  • Interveinal chlorosis (yellowing) in older leaves.
  • Upward curling of leaves along edges
  • Yellowing of leaf edges with green "Christmas tree" along the middle of the leaf.


The sulfur mineral is taken up by plants as sulfur as negatively charged ions or anions (AN-eye-uns). Sulfur may also be taken up by plants from the air through the leaves in areas where industrial pollution from the burning of fossil fuels is enriched with sulfur compounds. Who says plants don't fight air pollution?

Certain amino acids essential for plant health, (cysteine, cystine, and methionine) contain sulfur and are necessary for the synthesis of proteins. Sulfur is present in certain plant oils, which accounts for the odor of onions and garlic. It is also essential for nodule formation in certain types of plants that take nitrogen out of the atmosphere and fix it in the soil within the nodules. This family of nitrogen fixing plants is known as "legumes", and will be discussed further in this book as we go along. Sulfur is often applied to these plants to stimulate better nodule formation in order for legumes to fix more valuable nitrogen into the soil.

Sulfur is also known to suppress the growth of certain plant diseases and is often combined with calcium carbonate (Lime) in commercial fungicides that natural gardeners find very useful.

Alkaline soils are often low in sulfur and sulfur is applied to these soils to lower pH values and brings the pH more toward neutral. Sulfur is applied to soils in the form of soil sulfur, Sul-Po-Mag, Iron sulfate, and other sulfate compounds. Signs of deficiency are:

  • Young leaves are light green or yellowish in color. In some plants older tissue may also be affected
  • Plants are small and spindly
  • Interveinal chlorosis on plants on grasses
  • Plant growth is retarded and maturity is delayed


Ample amounts of iron are required for plants to make chlorophyll which is the normally green pigment that is essential for photosynthesis. It also is an important activator of certain biochemical processes such as respiration and symbiotic nitrogen fixation. Plants take up iron in the form of positively charged ferric or ferrous ions.

Iron availability is affected by soil pH and when soils are alkaline iron is blocked. This is one of the reasons that iron chlorosis (interveinal yellowing) of foliage is so common in soils with a high pH. Lawns use a lot of iron and are often yellow due to a deficiency of this mineral. Gardeners often mistake an iron deficiency for a lack of nitrogen in their lawns and feed their lawns with high nitrogen fertilizers that only green up their lawns temporarily. It is a good idea to identify when an iron deficiency is the cause of yellowing foliage. Checking the pH of your soil easily does this. If the pH is high and you fertilize regularly, chances are you can keep your lawn greener by adding an iron supplement to your soil instead of giving it another dose of nitrogen fertilizer. One thing to remember when applying iron to the garden is to keep it off of sidewalks, driveways, and paved areas. It makes rust, which is very difficult to remove.

Some common iron supplements are iron sulfate, iron phosphate (which is also a very good snail control material), and blood meal. Blood meal provides iron to your soil while it adds nitrogen. Some signs of iron deficiency are:

  • Interveinal chlorosis of young foliage. Veins remain green while leaves yellow.
  • Twig and dieback of young growth
  • Tissue death in severe cases


Zinc is taken up by plants as the positively charged zinc cation. It is an important constituent of several enzyme systems and it controls the synthesis of certain essential plant growth hormones. Zinc is often the micronutrient most often needed in western soils and its' availability is affected by soil pH, much in the same way iron availability is.

Zinc is supplied to soils and directly to plants. It is available to gardeners and farmers in both liquid and granular forms. Zinc sulfate, which is also a source for sulfur is one of the most common types of zinc compounds produced for gardening and for farming use. Citrus fruits, grapes, tomatoes, and other tree fruits are known to use large quantities of zinc. Symptoms of zinc deficiency are:

  • Reduced bud and fruit production
  • Crinkling of new growth and a decrease in stem length
  • Interveinal chlorosis (often misdiagnosed as a iron deficiency)
  • Dieback on year-old growth

Next time we'll be looking at three more mineral nutrients that are used in very small amounts by plants and are commonly referred to as "micro-nutrients or trace elements" that are essential for your precious green friends. See you in the Garden!

Got Questions? Email the Doc at
Check out Donald Trotter's books Natural Gardening A-Z, The Complete Natural Gardener and Rose Gardening A-Z at

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