Creating the Right Orchid Mix

Hort Americas partners to produce an orchid growing substrate made with pine bark

orchids account for the largest wholesale value ($96.8 million) of the orchids
sold in the United States, according to the USDA
2007 Census of Agriculture
. Phalaenopsis orchids are unlike most other
ornamental flowering plants produced by commercial growers. In their natural
habitats, most of these orchids are epiphytic, living on trees with their roots
exposed to the shaded, humid environment in which they thrive.
Orchid mix considerations
Steve Jarahian,
director of technical services at Oldcastle Lawn & Garden Inc., said the
growing medium used to grow phalaenopsis orchids is more open than traditional
peat-perlite mixes.
“When these
orchids are grown in a container, we are trying to provide an environment that
will give the roots enough air,” Jarahian said. The other criteria required for
traditional growing media still apply. The mix has to have the ability for the
orchid roots to absorb water and nutrients. Depending on the type of orchid
grown, if it has a very coarse root system, the plants need support.”
Jarahian said the
bark typically used for orchid growing mixes in the United States has come from
European or local sources. Growers on the West Coast have used redwood bark,
fir bark or osmunda fiber. He said other components of orchid mixes have
included expanded shale, clay and activated charcoal.
“With the
difficulties and cost of freight for shipping bark from Europe or from other
parts of United States, what we are trying to do is duplicate these other
growing mix components using locally-grown pine bark,” he said. “We are doing
something that is not typically done with pine bark.”
Lawn & Garden has partnered with Hort Americas to develop and produce an
orchid growing mix made from larger size pine bark particles. Jarahian
considers the phalaenopsis orchid growing substrate that is available from Hort
Americas for commercial growers to be a medium-coarse mix.
“The particular
bark that we are working with is about 5/8- by ½-inch thick,” he said. “It’s a
solid thick particle so that it can provide enough air. It’s almost as thick as
it is wide.
“Other growing
mixes may contain bark particles, but they tend to be thin, smooth and
plate-like. The Hort Americas orchid mix bark is fairly light and has a rough
surface. That helps with the air space and how the roots adhere to the surface
of the particles. This bark wouldn’t be used to grow geraniums, poinsettias or
mums. Also, the orchid mix pine bark is not aged.”
Jarahian said
that the orchid mix bark comes from pine trees that are over 15 years old. Bark
from younger trees tends to be more flake-like. Multiple screenings are needed
to produce a consistent particle size with the thickness that is needed.
Jarahian said he
prefers the pine bark used in traditional growing mixes to be between nine to
12 months old. For the orchid mix, the bark needs to be no older than two to
four months old.
“Bark that is 12
to 18 months old is going to absorb water and it’s going to break down,” he
said. “The newer the bark the more consistent the mix will be in regards to
wetting and drying. If the bark absorbs too much water, then the grower can
encounter problems with Phytophthora root rot. Also, since older bark is going
to absorb water, fewer pallets of the orchid mix will be able to be shipped per
truckload because of the additional weight raising the freight costs.”
Other mix components
A spongy, fibrous
sphagnum moss imported from Chile is also incorporated into Hort Americas’
orchid mix.
“It’s the actual
sphagnum plant, not the decomposed sphagnum peat used in traditional potting
mixes,” Jarahian said. “The moss is added to provide some moisture holding
He said the
amount of moss that is incorporated can be reduced to increase the air space in
the mix. Lime is also added to the mix because pine bark tends to have an acid
Jarahian said
initially a starter fertilizer charge was added to the mix. The fertilizer is
no longer incorporated enabling growers to better control the soluble salts
“We were putting
in a nutrient charge, but because of how pine bark ages, there was some
variability in the soluble salts level. On occasion a spike in the soluble
salts was hindering plant rooting.”
Johann Buck, Hort
Americas technical service manager, said the orchid mix produced in Europe
contains a starter fertilizer charge because without it growers were
experiencing a one to two week delay in production.
“This is due to
nutrient tie-up, usually nitrogen,” Buck said. “The age of the bark used in
Europe is much older than the U.S. bark. This means there is little fluctuation
in electrical conductivity (EC), so the European mix manufacturers can add a
starter charge.”
Buck said since
the U.S. bark is younger and due to the nature of the aging process, there can
be undesirable increases in the EC level.
“When orchid
plants, especially young plants, are exposed to EC levels above 0.8
milliSiemens per centimeter (mS·cm-1), root burn can occur,” he
said. “This can delay growth. Other containerized crops can tolerate an EC of
0.5 to as high as 3 mS·cm-1. With orchids the EC level has to be
constantly monitored and should be in a range of 0.5 to 0.8 mS·cm-1.
Everything that is done from week 1 to the day the plants are harvested impacts
For more: Steve Jarahian, Oldcastle Lawn & Garden Inc.,; Johann
Buck, Hort Americas,;

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