The Dirt on Soil- Indoors
Most of the tropical plants we care for indoors come to us potted in a blend of peat, sand, vermiculite and coir. Peat is the partially degraded material left when mosses and ferns die seasonally and form a mat in acidic and anaerobic conditions. The peat we see is typically of Canadian origin. Sand is very small rounded pieces of rock. Vermiculite is expanded hydrous phyllosilicate mineral. It originates in mines in Russia, South Africa, China and Brazil.
Coir is the fiber from the outer husk of the coconut. This combination is considered a soilless mix, as no topsoil is used in the blend. Both the peat and the vermiculite hold water well, but are light in weight when dry. The sand gives heft and stability, and the coir seems to attract beneficial bacteria and is completely renewable.
I can remember back in the 1980s, when the larger tropical trees came to us in metal grow cans and potted in the native marl soil. These trees usually dropped most of their leaves as they attempted to acclimate to Michigan light and humidity. Their chances of survival were further endangered by the difficulty of watering evenly in the marl, which was hard and almost rocky in structure. Like watering clay, it was prone to uneven absorption and once dried, was difficult to re-wet. Today’s mixes are uniform and lightweight, with a fairly neutral and predicable pH. The weight is important when considering how many times each plant is lifted and moved in production, and later for shipping and then installation. Even water absorption is essential for growing a quality crop. Neutral pH allows for good uptake of fertilizer- the plants’ nutrition source