I would like to use pre-buffered coco. What is a well-buffered coco?

Q:

Your articles on buffered coco are quite educative and interesting. I would like to use pre-buffered coco and would like to know what you would call a well-buffered coco? What should be the K, Na and Ca content of a well-buffered coco be, without creating a nutrient imbalance to my plants?

A:

Coco coir is known for having good cation exchange capacity (CEC). This is basically a measure of negatively charged sites in the medium that positive ions can attach to.

Unbuffered coir has many of these sites filled with potassium (K) and sodium (Na), which both have a single positive charge. Double positive elements such as calcium (Ca) and magnesium (Mg) have a stronger affinity to these sites, and will replace potassium and sodium.

This can cause a nutrient imbalance if the calcium and magnesium intended for plant use is instead captured by the medium that in turn releases the displaced potassium and sodium. In this scenario, there is a possibility for shortages of available calcium and magnesium, and an overabundance of available potassium and sodium.

One way to minimize this issue is to subject the coir or expose it to a solution with calcium and magnesium before use. This will allow the exchange to take place and some of the excess potassium and sodium to be removed.

Since more of the cation sites will already be filled with calcium and potassium from the treatment, it will have a smaller fluctuation when exposed to more calcium and potassium during plant feedings.

For practical purposes, some treatment is noticeably better than no treatment, but there is a point of diminishing returns where replacing more of the cation sites requires more resources than it provides improvement, as both potassium and sodium have nutritional value as well.

The amount of buffering agent to use will depend on the condition of the starting coir, and the particular agent used. Coir manufacturers calculate how much they use to get the desired result, and one reason pre-buffered coir has become so popular is because it takes care of much of the math and chemistry for the consumer.

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Grubbycup has been an avid indoor gardener for more than 20 years. His articles were first published in the United Kingdom, and since then his gardening advice has been published in French, Spanish, Italian, Polish, Czechoslovakian and German.
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