Coco coir is the fibrous material derived from the husks of coconuts, a byproduct of the coconut industry. It is used as a growing medium due to its excellent water retention and aeration properties. Unlike organic materials such as peat moss, which decompose relatively quickly, coco coir is chemically stable and does not rapidly break down. While the material itself is durable, its functional quality can decline over time, particularly when exposed to moisture or after being used for growing plants.
The Longevity of Coco Coir in Storage
The exceptional longevity of dry, unused coco coir is due to its unique chemical composition, primarily its high lignin content. Lignin is a complex organic polymer that provides structural support to plant tissues and is highly resistant to microbial and fungal breakdown. Coco coir can contain between 30% and over 40% lignin, making its decomposition rate slower.
If stored correctly in a cool, dry environment, compressed or loose coco coir can remain viable for use for several years, sometimes up to a decade. The inert nature of the material means that biological rotting is not the primary mechanism of degradation when dry. Instead, any decline in quality over long periods is typically physical, with the fibers breaking down into finer particles known as “fines.” This physical breakdown can eventually reduce the coir’s air-filled porosity, which is the space available for oxygen in the root zone.
Contamination Risks from Improper Storage
The main reasons coco coir becomes functionally unsuitable, or “bad,” relate to improper storage conditions or contaminants introduced during previous use. Once the coir is exposed to sustained moisture, it loses its inert quality and becomes susceptible to biological contamination. Mold and various fungal spores, such as the common green mold Trichoderma, can germinate and spread throughout the substrate, especially if the storage area is warm and humid.
These biological agents can negatively affect new plant growth by competing for resources or introducing pathogens that cause seedling dampening or root rot. Another risk is the accumulation of mineral salts, which occurs if the coir was used previously or was poorly washed during manufacturing. High levels of these residual salts, measured as elevated electrical conductivity (EC), can burn plant roots and impede nutrient uptake, leading to salt toxicity.
The cation exchange capacity (CEC) of coco coir is another factor that deteriorates with use or age. Coco coir naturally possesses a high CEC, meaning it holds onto positively charged ions like potassium, sodium, and calcium. If the coir was not properly pre-buffered or was used with nutrient solutions high in potassium or sodium, those elements can bind to the coir and be released unpredictably during a subsequent grow cycle. This imbalance can lead to nutrient lockouts, where calcium and magnesium are prevented from reaching the plant roots, causing deficiencies.
Preparing Stored or Used Coir for Reuse
Safely reusing coco coir requires addressing the potential problems of salt accumulation and biological contamination.
Rinsing and Leaching
The first step involves aggressive rinsing or leaching to remove residual salts and fine particles left over from the previous growth cycle. This is achieved by flushing the coir thoroughly with clean water, such as reverse osmosis or distilled water, until the run-off water’s EC level drops significantly.
Buffering
The next action is buffering, which is important for coir that has been used or stored for a long time. Buffering involves soaking the coir in a solution rich in calcium and magnesium, often using a specialized Cal-Mag supplement. This step effectively recharges the coir’s cation exchange sites by allowing calcium and magnesium ions to displace any bound sodium or potassium.
Sterilization
Finally, to address any potential pathogen or mold contamination, the used coir should be sterilized. While commercial growers may use chemical treatments, home growers can use methods like solarization, which involves spreading the coir out on a plastic sheet in direct sunlight for several days to allow heat to kill mold spores and harmful bacteria. Alternatively, using an enzyme product can help break down any remaining dead root material into usable organic compounds.