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| | | | Growing Media - I
The Purpose of Growing Media
Luxury conditions: plenty of water and fertilizer, adequate temperatures, and freedom from diseases and insects are required for growing Indoors and seedlings. These conditions provide for fast growth and high survival rates but increase requirements to the quality of the growing media.
A quality growing mediamust have certain chemical and mechanical properties. Chemical properties include having the proper pH and Caption Exchange Capacities to allow nutrient availability to the plants. Mechanical properties, include providing an anchor for the plants, making oxygen and water available to the roots, and acting as a reservoir for nutrients.
Focus on the Roots
Growing media forms the environment in which the roots grow. An ideal growing media must be judged based on it's value to the roots Plants take up water and dissolved nutrients through small hairs on the roots, and a large well developed root system is required for well performing bedding plants..
Water or Air ?
Root hairs are tiny numerous extensions of the roots and they require constant moisture. The root hairs take up oxygen and release carbon dioxide continuously, requiring air (gasses) to pass in and out through the growing media; a process called gas exchange. If exposed to dry air even for a few minutes they die, but on the other hand, they can not withstand being totally immersed in water for too long either.
The ideal environment is thus one which is rich in oxygen and saturated with water vapors. As water uptake and gas exchange take place in the same pore space in the growing media, they are unfortunately also mutually exclusive.
A growing media can consist of almost any type of solid material (peat moss sphagnum, vermiculite, sand, etc) as long as it is capable of striking a suitable balance between air and water at the same time. The sizes and shapes of these pore spaces are also referred to as the growing media's "porosity". The solids themselves are actually somewhat irrelevant; the interesting properties are the pore spaces which they form.
Porosity
Depending on the materials used in the mix the pore spaces formed in the growing media will have different sizes and shapes.
For example, fine materials, such as peat moss sphagnum will create small pore spaces whereas materials made up of large particles, such as perlite, will create large pore spaces.
The interaction between these materials are even more important. This will reduce the overall air holding capabilities of the media while increasing the water holding capabilities. For example, fine-particle media added to a coarse mix will result in the finer particles settling in the cavities between the larger particles.
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