CALCIUM The Soul of Soil & Plant Health 
By Don Trotter 



Hello fellow Earthlings, and welcome to a series of articles on the minerals and nutrients that make our precious plants grow. Our first article will be on my personal favorite mineral for soil and plant vigor. So let’s take a stroll out to the garden. 

Calcium has always taken a back seat to the “big boys” of soil fertility. The industry buzz is usually nitrogen and new forms are frequently being released to the market. Referred to as a secondary nutrient behind nitrogen, phosphorous and potassium, calcium is finally starting to take its place in the ranks of important plant nutrients. It is true that NPK is used in greater percentages than calcium, but calcium is used more by weight and volume than any other nutrient. 

Practically speaking, calcium is rarely considered as a nutrient at all! Instead the focus on calcium has been more as a soil buffer to help adjust pH. Calcium is of huge importance to both the plant and the soil in many more ways than simply moving the pH scale. It plays a major role in the physiology of the plant, strengthening its physical structure and helping in protection from disease attack. 

In the soil, the importance of calcium is many fold, including the reduction of soil compaction and helping to provide a better environment for the proliferation of beneficial microbes. Some research even suggests that calcium plays a role in decreasing weed populations. 

Imagine the room that you’re sitting in is a plant cell of your favorite plant. The walls that surround you are made of calcium pectase (if you were inside a plant, calcium pectase would be the least of your problems). The more calcium that is available to that cell, the stronger those walls become. 

If calcium is limited the walls are as weak as jelly. As more calcium becomes available, those walls take on the strength of cinder blocks. The stronger the cell, the stronger the plant, and the quicker its recovery from the enormous pressures that it is faced with in the garden. This works for both leaves and roots. The stronger the root cells are, the more aggressively the roots will be moving through the soil. Proper levels of calcium within the plant strengthens the whole plant and allows for efficient use of sunlight, carbon dioxide, water, nitrogen and mineral nutrients. 

Calcium also plays a major role in the construction of numerous hormones, and enzyme systems that can help protect the plant from insect and disease attack. It has been reported that as a pathogen probes its way into a cell, it injects an enzyme to help break that cell down. There is research that suggests, as this occurs, proper levels of calcium within the cell can actually slow this attack down, or stop it all together. The levels of calcium within the cell are going to be dictated, to a large extent, by the management of calcium within the soil. 

Calcium plays many roles in the soil, but it is the relationship with other nutrients such as magnesium, potassium and sodium that are most significant. To associate calcium only as a buffer of pH in the soil is an injustice. In fact, pH can be driven by numerous minerals, like magnesium, potassium, sodium, or even aluminum. Often calcium is applied to the soil to lower pH. It is important to understand that an imbalance of calcium will lead to tight, hardpan soils, which will restrict the flow of air and water through the soil profile. This will not only affect the plant roots, but perhaps even more important, slow down the growth of beneficial microorganisms. 

The soil is an extremely dynamic environment consisting of numerous chemical, biological and physical reactions. It is on all three levels that we must manage the soil. We can change the physical structure of a soil by properly managing the chemistry, thus providing a stronger biological environment. It is this biology that is so important to the success of managing any crop. For the first time in recent memory soil biology has risen to the forefront. If we are going to make any improvement in the health of our plants, proper soil management is imperative and this all starts by managing calcium levels in the soil. 

Dr. William Albrecht, the former head of the Soils Department at the University of Missouri, established the protocol for balancing the basic minerals on the soil colloid more than 50 years ago. Today that research is the backbone behind a growing interest in sustainable soil management. Many of the pre-eminent soil-testing laboratories use this methodology today. His research focuses on the soil tests’ base saturation readings, where calcium plays the largest role. 

When imbalances among minerals occur, the soil becomes very tight and air and water can not penetrate (sound familiar?). When this occurs roots are not the only things that suffer; beneficial bacteria suffer as well. These are looked at as heavy, unmanageable soils, and excessive mechanical aeration appears to be the only help. Unfortunately, this aeration does not address the real problem. 

There are a number of good ways to supply calcium to a soil. Several types of lime are often used in certain parts of the country, high calcium lime, or calcitic lime, and high magnesium lime/dolomitic lime. Depending on the source, calcium levels can vary from around 30% to 45%, but the real difference is that percentage of magnesium. High calcium lime will have a magnesium reading of about 5% while dolomitic lime will read closer to 20%. This difference in magnesium is significant since it will drive pH up faster than calcium and will quickly create a tight soil. In soils with excessive magnesium levels dolomitic lime would not be appropriate, and in fact can create worse imbalances in the soil. 

Gypsum or calcium sulfate is typically around 23% calcium and 18% sulfur. It has this magical reputation of reducing soil compaction, which it will do in many situations, but is often misused. Gypsum is not very effective in a soil that shows less than 60% base saturation calcium. A soil with a significant calcium deficiency often needs large quantities of calcium to saturate the soil colloid. If this is applied as gypsum, too much sulfur is being applied and other problems can occur. It is important to use the appropriate type of lime on calcium-poor soils. 

Recently a discovery in the Nevada desert has produced another, and presently the most superior source of calcium yet researched. This material is a seabed mineral that includes fossilized remains of marine plants (macroalgae) or sea kelp/seaweed. The product is being marketed to farmers, growers, and turf professionals as Kelzyme. This high calcium (up to 50% available) also contains more than 75 trace elements, 1% sulfur to dislodge magnesium from soil colloids, and 1% iron to keep chlorosis at bay. 

This material has also drawn to the attention of growers and researchers the apparent importance of Silica (Si) in drought and frost resistance as well as additional cell wall strengthening for pest and disease resistance. It has only been available in bulk quantities from Environmental Health Science Corp. in Provo, Utah. But California Vermiculture, a company involved in the retail sales of superior quality worm castings, has taken on the task of getting this material out to the public. California Vermiculture can be reached by contacting George Hahn at (760) 942-6086 or going to their website at  

Calcium is an extremely immobile nutrient. If it is appropriate to use gypsum, mobility can be improved slightly. But watch out for that sulfur. It is imperative that we balance the calcium in the soil so we can provide the environment that microbial populations need to proliferate, but it is also very important we provide the plant cell with calcium. This is how it can lower the soil pH, which is getting a lot of attention for disease suppression. Is it possible that this available calcium may play a role in disease suppression? Dr. Curly says “You betcha!” 

Calcium perhaps plays more roles in the overall health of both the plant and the soil than another nutrient. If well balanced on the soil colloid it will help to physically open up the soil for better air and water movement. This in turn provides the needed environment for beneficial bacteria creating checks and balances for disease. It helps in root and leaf development and makes phosphorous and micronutrients more available. 

If well balanced the proper levels of calcium are going to help reduce the need for nitrogen by making organic matter decomposition more efficient. As Dr. Albrecht explains in his volumes of research, if we get the calcium right in the soil most of our work is done. See you in the Garden! 

Got Questions? Send the Doc an e-mail at  Don Trotter’s natural gardening columns appear nationally in environmentally-sensitive publications. For more helpful gardening tips, check out Don’s books “Natural Gardening A-Z” and “The Complete Natural Gardener” available at bookstores near you and all online booksellers, both from Hay House publishing.

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