|
From tigereyes@dclink.com Wed Aug 7 20:46:42 1996
Subject: <none>
To: ahicks@mailhost.nmt.edu
{TigerEyes' comments: this is some info I recieved in response to a
request about "pet potting mixes". I thought you might find it
interesting ;} --julia}
Here is another addition to your media list--Wally
ORCHID
CULTURE IN PERLITE
Wally Thomas and Barb Thomas
For a long time perlite has been known as a beneficial soil
conditioner.
Starting some 15 years ago at the West of Scotland Research Station, a
technique was developed to use pure perlite in growing tomatoes.(1) The
technique made use of a water reservoir to maintain a constant fertilizing
of the crop by taking advantage of the excellent capillary action of
perlite. Studies on tomato culture were carried out comparing production
using this perlite technique and rockwool culture. The perlite proved to be
superior and much simpler to manage. Since 1988 we have adapted this
perlite technique to growing orchids with excellent success. It should be
noted that Pierce(2), in 1983, reported excellent results growing
Phalaenopsis in pure perlite culture even without the reservoir technique.
Perlite is a volcanic rock that occurs worldwide. The two largest
deposits
are in Greece and in the State of New Mexico in the United States. The raw
material is shipped around the world to factories, where it is processed
for local consumption. The rock is heated to 1000oC and the small amount of
water contained in the rock is turned into steam which expands the rock into
a light weight material almost like making popcorn. It is then graded for
size, although at the present time there are no internationally recognized
standards for size. The grade that is readily available is usually called
Horticultural grade and this is what we use.
Table 1 gives a comparison of the horticultural features of bark, peat,
rockwool and perlite. Some aspects are of particular importance.
1. Ease of potting - Those who have now tried this technique are in
agreement that it is the easiest potting technique they have ever used.
2. The material is free draining and it is virtually impossible to over
water. At the same time it maintains excellent aeration. Immediately above
a water reservoir the perlite holds 30% of its volume as water, and at 8"
(12 cm.) above the reservoir it still has 19%. Thus, it has a combination
of both excellent aeration and a continuous supply of nutrients in the
water. Being neutral in pH it allows for complete control of fertilization
while, at the same time, it is easy to leech out any accumulation of salts.
Two undesirable aspects are:
1. The dust and
2. The occasional occurrence of compaction.
Both of these however, are easily dealt with in the following technique.
Horticultural grade perlite is used, (usually the only perlite
available),
and it is usually packed in 4 cu. ft.(110 liter) bags of plastic or paper.
We find that plastic bags provide a better seal for the dust that may be
present. There are many suppliers of perlite and it is worthwhile trying to
find a manufacturer who produces a 'clean' low dust perlite. We prepare
the perlite outdoors (if possible) by pouring 1/3rd of a sack into a garbage
tub that is half full of a fertilizer/water solution. The surface is
briefly hosed and then the perlite is pushed down into the water. In a
short time the fine material sinks to the bottom and with it gone there is
no further concern with compaction. What is left floating is a light airy
medium that one may scoop out with one's hands into the pots or take out
with a colander. Intermittently the fine material that has accumulated in
the bottom of the tub is scattered in the garden.
POTS AND POTTING
To take advantage of the water reservoir technique one needs either
pots
that are made with a reservoir or ordinary pots must be provided with a
reservoir. Ordinary pots may be used by cutting a strip of fiberglass
window-screening and putting it around the inside at the bottom of the pot,
so as to contain the perlite in the pot. Then a plastic container
(300-400 ml. size for a 6" pot) may be placed so that when the pot is
watered this container will fill with water which will later be available to
the roots by capillary action. KORD manufacture both 8 and 10" (20 and 25
cm.) saucerless hanging pots. They have water reservoirs of 300 ml. and
500 ml. respectively. These pots provide aeration from below as well as
acting as an insect barrier. Our favourite pots are the 'Cameo Line' made
by Haney Pottery (7890 Vantage Way, Ladner, B.C. Canada: Green Arrow,
Sepulverda, Ca.). They are made of heavy very long lasting plastic with a
detachable saucer on the bottom and are available in 5 and 6 1/2" sizes,
(12.5 and 15 cm.). They do however require some screen or pebbles to
partially cover the drainage holes which otherwise would allow the perlite
to escape. Any plastic container may be converted to a reservoir pot by
drilling holes in the side to give a 1-1.5" reservoir in the bottom. The
hole size should be 3/8" (0.95 cm.), the size is quite critical. Window-box
type plastic containers are also excellent, the Haney product being 7" (18
cm.) high and across at the top, and 6" (15 cm.) across at the bottom and
22" (55 cm.) long. Three holes are drilled at each end about 1.25" above
the bottom.
POTTING:
SEEDLINGS
The KORD 8 and 10" (20 and 25 cm.) pots are particularly suitable for
seedlings out of flask. The pots are filled to about 1" (2.5 cm.) from the
rim of the pot and the seedlings planted. The surface is carefully covered
with small pea gravel such that the perlite cannot be seen. The metal
hanger is then placed in the appropriate holes in the rim and a cling wrap
material is wrapped around leaving an opening at the top much like a
teepee. It allows for some aeration, yet maintains a micro environment with
suitable humidity. We maintain the Odontoglossum seedlings at a minimum
temperature of 60oF (16oC). The containers are bottom watered once a week
by dipping the pot about 3" (7.5 cm.) into a fertilizer solution that is 1/2
the strength used for adult plants. i.e. EC of 250-300uS and the EC of the
reservoir solution is carefully followed. The cling wrap material is best
left on for about 6 weeks, and at this time the fertilizer strength is
increased to an EC of 500- 550 uS.
REPOTTING:
Young seedlings may be moved into perlite at any time, however, larger
plants should only be moved into perlite from other media when they are
showing new growth. This allows a new and different root system, adapted
to the perlite, to develop. The old medium should be thoroughly removed
from the roots and all dead roots removed. The plant is then held in
position, and the wet perlite scooped into the pot. It is vital that the
plant be slightly deeper in this media than with other media, the reason is
that sometimes, when the plants have been in the pot for a year or so, the
large root system may push the plant up a bit. The perlite is then leveled
and gently pressed after which the surface is covered with a layer of pea
gravel. The gravel layer has 3 functions.
1. It prevents the newly potted plant from moving when it is watered.
2. It prevents the perlite from being washed out when watering.
3. It prevents the occurrence of surface evaporation with attendant
salt
build up.
The smallest pots used are 4" (10 cm.) in diameter as larger sized pots
maintain a more uniform environment. Small plants are all grown in community
pots. Repotting from perlite to perlite is done by simply lifting the plant
out of the one pot and if no trimming is required it may be placed in the
second pot with considerable perlite remaining attached. Additional perlite
is then scooped in and gravel applied to the surface. This method allows
both young and old plants to go from perlite to perlite with virtually no
setback. There is no concern about leaving plants in perlite for two or
three years as there is no change in the medium (we have never seen
compaction) and rot is not a problem. This is of particular value when you
pollinate a plant that has been in the pot for 2 years yet having
pollinated it, you are now reluctant to repot it. Ideally repotting
should be done every two years. We use fresh perlite in repotting and use
the old perlite for growing strawberries, tomatoes, daffodils and dwarf
fruit trees all of which grow very well using the reservoir technique. The
used material may otherwise be spread in the garden where it makes a most
welcome addition to most garden soils.
PERLITE BEDS:
In order to further simplify the management of perlite we constructed
beds
that offer a large reservoir volume and reduce the frequency of watering.
The beds are 8" (20 cm.) deep and are constructed of plywood on the bottom
and 1" by 8" (2.5x20 cm.) cedar sides. A sheet of plywood is conveniently
cut into three pieces 32" (80 cm.) by 48" (122 cm.) to make 3 beds. They are
lined with double 6 ml. polyetheleyne. Drainage is provided by a plastic
3/4:(2 cm.) through-hull fitting situated on one of the sides 1.5" (4 cm.)
up from the bottom. The drainage water may then be readily collected for
recycling or use elsewhere in the garden. After checking for leaks a square
piece of fiberglass screening is placed over the hole and the bed filled
with perlite. The bed must be level and strongly built because when full it
will be very heavy.
When potting in the bed the orchids are again set slightly deeper than with
other media and covered with a layer of gravel, about 1/2". We have had
such beds in operation for up to four years and they have shown no evidence
of infection in the plants nor any compaction of the perlite. We have
grown both seedlings and adult plants in the beds and both do equally well.
Unfortunately, one cannot transport the bed to a show. We water beds and
pots once a week during the Winter and somewhat more frequently during the
Summer. It is important that the reservoirs do not go dry, although the
perlite is easily re-wetted. Although initially we flushed out the beds and
the pots every two months, during the past 18 months we have been
fertilizing at each watering but water heavily to make sure that there is a
significant overflow.
In 1988-89 36 matched Odontoglossum seedlings were grown in rockwool and
perlite. At the end of a year there was no significant difference in their
growth as measured by weight and leaf length. The plants in perlite seem to
make a slightly slower start but caught up at the end of a year. The root
system in perlite is much larger than that in rockwool. In the ensuing years
the plants did so well in pelite that we moved our entire collection into
perlite in the spring of 1992 and since then have recieved 3 AM's and 4
HCC's. We have had excellent growth with Odontoglots, Oncidiums,
Masdevallias, Lycaste, Cymbidium and Miltonias. Using this technique others
have had excellent results with Cattleya, Phalaenopsis, Dendrobium and
Paphiopedilum.
Orchids have been grown hydroponically since the early 1930's when
Dr. Burgeff in Germany grew and bloomed Phalaenopsis in beer steins
containing only fertilizer solution and at the same time Dr. Eversole in
California also grew them and bloomed them in gravel hydroponic culture.
Eversole grew Odontoglossums with equal success. Somehow in the ensuing 60
years the majority of orchids have continued to be grown in Osmunda, peat
and bark along with a host of mixes and more recently, rockwool. Although
rockwool and perlite are 'true' hydroponic media, the others offer very
little nutrition to the plant.
WATER:-- Since orchids only require a 1/4 to a 1/6th the nutrient
concentration of more rapidly growing plants, it is vital to know the
makeup of the water supply being used. The water should have a low salt
content. Although rainwater is the best, this may be difficult to obtain
and one may have to use a mixture of rainwater and the local water supply,
or perhaps put in a reverse osmosis unit.
Investigation of the water supply may be broken down into two parts.
1. The total quantity of salts
2. The qualitative analysis of the salts
QUANTITATION OF SALT CONTENT:
A reasonably accurate and very practical means of assessing the salt
content of water is to measure the electrical conductivity (EC). Pure water
conducts an insignificant amount of electricity, but most salts will allow
for conductivity and for these there is a direct relationship between the
concentration of the salt and the EC. The conductivity is measured in units
that are either called MHOS (this is ohms (resistance) in reverse) or as
SIEMEN(S). For orchids the level of conductivity you wish to measure is
extremely small and is measured in millionths, called micro and expressed by
the symbol 'u'. Thus, one would express a reading of 100 as 100uMHOS or
100uS. In horticulture there is an increasing use of Siemens as the unit of
measure. The instrument that is used to measure the conductivity is called
a conductivity meter and it operates by passing a small electrical current
between two electrodes. Unfortunately, meters may be calibrated in two
different ways. Some meters read in Siemens(MHOS). others meters are
calibrated to read as Total Dissolved Salts (TDS). The TDS is supposed to
be calibrated so that it will give a reading in parts per million (PPM)
however this is misleading for salts have varying conductivity (some such as
urea do not even conduct electricity). Most of the horticultural papers use
Siemens, i.e. the electrical conductivity unit , however some city water
works may give their water analysis values in TDS. Such values are easily
translated as the two meters are calibrated so that 1000 uS is equal to 666
TDS. It is important, then, to obtain a meter that reads in Siemens and
also reads in the range that is suitable for the particular plant that you
wish to grow. For orchids a small satisfactory hand held meter is the TDS
Tester 3, (Cole Parmer Co. 7425 North Oak Park Niles ILL60714) which reads
from 0 to 1999 uS and is ideal. This meter is also calibrated to correct
for temperature, as a low temperature significantly reduces conductivity.
Test solutions are also readily available to check on the calibration of the
meter. This meter, as well as the matching pH meter, runs on a small
batteries which are easily replaced.
Since orchids require such a low level of nutrition, it is important that
the water supply has a low levels of salts. In Table 2 an assessment of the
water rating for orchids is given.
QUALITATIVE ANALYSIS:
Not only should one know the total salt content of the water supply but
<<< Continued to next message >>>
to: INT:ahicks@mailhost.nmt.edu
cc: INT:Y.ISLAM@CGNET.COM
INT:nrach@lgc.com
INT:gardner@gp.magick.net
INT:dcurrie@oreo.uottawa.ca
|
