Propagation/Greenhouse ManagementUnit 1.3 | Part 1 – 121- Vermiculite
A micaceous mineral, vermiculite is mined and then processed in kilns heated to 1000ºF.
While in the kilns, microscopic water molecules trapped in the ore are vaporized, which in
turn causes the ore to exfoliate, accordion style, into a material that has a huge surface to
volume ratio.
a) Outstanding ability to hold water, at least four times its own weight
b) High cation exchange capacity (CEC) and especially effective at holding on to K, Mg, Ca,
and P
c) By virtue of its size and shape, provides good drainage and aeration, while also being
lightweight and easy to handle
d) Is sterile when first removed from its packaging and is therefore not a source of weed
seeds or pathogens, and has a pH of 7.0
e) Produced domestically in South Carolina and Virginia, imported from South Africa,
Brazil, China, and several other sources
f) Alternatives to vermiculite include partially composted cotton gin waste, ground pine
and fir bark, sand, and leaf mold
- Peat moss
Derived from wetland bogs in many countries in the far North, consists of the remains
of partially decomposed sphagnum moss, and allied plants, held in a state of very slow
decomposition because of the water-saturated, anaerobic environment in the depths of
the bogs
a) An outstanding source for water retention, holding 4–6 times its weight in water, while
at the same time providing for good drainage and aeration
b) Brings high CEC potential to mixes, and has a pH of approximately 4.5
c) There is debate as to the sustainability of peat mining practices. Also, peat bogs are the
world’s largest carbon repositories and trap more CO 2 than even tropical rainforests. The
disruption caused by extraction releases huge quantities of CO 2 into the atmosphere,
adding to greenhouse gases even after sites are restored.
d) Alternatives to peat moss include coco peat, partially composted wood waste,
mushroom compost, locally harvested leaf mold, and perhaps in the future, dairy waste
fiber sourced from anaerobic digesters
- Coco Peat/Coir Fiber
A byproduct of the coconut industry, coconut husks/fibers were once disposed of, but now
have become a significant input in the horticulture industry, often used in place of peat
moss in nursery and greenhouse operations
a) Has outstanding ability to retain water, roughly six times its own weight, while at the
same time providing for good drainage and aeration
b) Has good CEC capacity and is a small source of NPK at .5-.03-.25 and an average pH of
6.5
c) If not properly leached before packaging and shipment, can contain excess salts, which
are detrimental to most developing seedlings and subsequent growth; leaching of salts
consumes significant quantities of fresh water
d) Sourced in the United States principally from the Philippines, India, Sri Lanka, and
Madagascar, this ingredient has a carbon footprint needing further investigation given
its long distance transport to market
e) Alternatives to coco peat include locally harvested leaf mold, partially decomposed
wood wastes, mushroom compost, and perhaps in the future, dairy waste fiber sourced
from anaerobic digesters
Lecture 4: Soil Media, Fertility, & Container Formats