The choice of components is influenced by their availability and cost. Components may include composted hardwood sawdust, composted milled pine bark, milled coconut coir (coco peat), sphagnum peat moss,
perlite, coarse grade vermiculite, coarse sharp freshwater washed sand, soil, rice hulls, and peanut/groundnut shells.
Perlite helps provide good drainage, aeration and
friability.
Composition of the medium, that is, the ratio of the components, is largely determined by
the requirements of the group of plants to be grown. A potting mix requires components that retain ample available water and nutrients: such as peat, coco peat, sawdust, vermiculite, or soil; provide good drainage, aeration, and friability, such as
perlite, rice hulls, peanut shells, or pine-bark; and provide stability against top heavy plants falling over, such as sand, gravel, and soil. In addition, at least one of the components should provide a good buffer capacity and cation exchange capacity.
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Vermiculite aids the retention
of water and nutrients in the potting mix: medium grade (left) and
coarse grade (right). |
A close up view of individual
pieces of coarse vermiculite exhibiting the many fine layers that
makes up each piece and among which nutrient elements, water and
air are held. |
What may be a very good quality soil rarely serves as a good potting mix on its own, and usually suffers from poor porosity and aeration, compaction and difficulty in re-wetting.
Coco peat is another potting mix component that retains
available water.
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Gio. W. Fichera
