Alternative Substrates

Alternative components for blending with pine bark in a nursery container substrate is not a new idea. Many research studies have investigated the use of industrial and agriculture by products as extenders for pine bark supplies. A comprehensive literature search would yield a very long list of materials that have been tested in nursery container research trials. Many alternatives show promise, but limiting factors for wide spread use of alternatives include: procurement and handling costs; transport costs; regional availability; a limited supply of uniform and consistent quality of product and guidelines for preparation and use of materials.

Alternative media materials are currently being explored by researchers. In trials, these components have been effective at helping substrates retain nutrients and water - resulting in plant growth enhancement.

clayIndustrial clay mineral aggregates have been investigated with encouraging results. Calcined clays (like those used in cat litter) retain nutrients, encourage drainage, and enhance airspace while stabilizing pH. Clay is the product of extreme weathering that has broken large mineral rock structures down to particles less than 0.002 millimeters in diameter. Due to its large surface area and nutrient holding properties, clay is ideal for controlling nutrient leaching from pots and retaining water.

Research findings have shown that calcined clay usage in an 8:1 pine bark to clay mix can give the following benefits:

  • Reduction of irrigation by 200,000 ga/acre in a season
  • Increased available water for plants by 4%
  • Plants with calcined clay remained turgid 48 hours longer than plants without calcined clay
  • Container substrates contained 100% more phosphorus
  • Reduced phosphorous leaching by 60%
  • Some clay lots serve as fertilizers themselves by providing calcium and/or phosphorous
  • Containers are 20% lighter
The use of calcined clay in potting mixes has been shown to reduce water and nutrient loss. It serves as a form of slow release fertilizer while reducing environmental impacts of highly nutrified runoff water.