REPOTTING
While young orchid seedlings may be transplanted at any time, larger
plants are best moved into perlite from other media when they show new
growth. The old medium should be thoroughly removed from the roots and all
dead roots cut off with sterile clippers. When repotting, the plant should
be held in such a position that the new growth has room in front for two
years growth. The wet perlite is easily scooped into the pot and plants
should be potted slightly deeper in this media than with other media, to
allow for a large root system which may push the plant up a bit. The perlite
is then leveled and gently poked down with the fingers to firm in the plant
and the surface is then completely covered with a layer of pea gravel so
that no perlite is visible.
The gravel layer has four functions.
1. It holds plants firmly in position.
2. It prevents washing out the perlite.
3. It markedly decreases surface evaporation.
4. It inhibits the growth of moss and algae.
In order to provide uniform conditions, we use community pot growing
until plants are ready for individual 4" (10cm) pots. In repotting from
perlite to perlite, tip out and save the gravel, then lift out the plant and
if no trimming is required and the roots look healthy, place it in the
second pot with perlite remaining attached. Additional perlite is then
scooped in and gravel applied to the surface. Plants will move from perlite
to perlite with virtually no setback. If necessary, plants may be left in
the same pot for three years. However, to achieve the best growth, repotting
should be done every two years. We wash and use the old perlite for growing
potatoes in plastic pails but most of it is spread in the garden as a fine
soil conditioner.
Beds and pots are watered once a week or less during the winter and more
frequently during the summer. We are currently considering a trial using a
recirculating watering system, but because orchids are long lived plants and
are susceptible to several viruses, one must be cautious.
It is important that the reservoirs do not go dry, although unlike
rockwool, the perlite is easily re-wetted. We fertilize/water heavily each
watering so that there is very significant overflow drainage and
periodically check the electrical conductivity (EC) of the overflow.
We did a trial comparing rockwool and perlite and at the end of a year
there was no significant difference as measured by weight and leaf length.
Odontoglots, Oncidiums, Cochliodas, Masdevallias, Lycastes, Cymbidiums,
Miltonias, Dendrobiums and Paphiopedelums have all shown excellent growth
with the reservoir technique. Phalanopsis however do not seem to like the
reservoir. If you have the time available for watering when needed the
reservoir may be omitted. Plants we have treated this way have done well,
though we have not carried out a comparative trial. If you are using
ordinary pots which frequently have fairly large drainage holes, gravel may
be used in the bottom to hold in the perlite.
We also use the perlite/pea gravel/reservoir technique to grow daffodils,
strawberries, potatoes (in dog biscuit buckets), tomatoes and many garden
annuals and herbs. Dwarf fruit trees also do well. The trees are grown in
large plastic barrels which are cut in half and 4 3/8" (10.2 cm) holes are
drilled about 3" (7.5 cm) up from the bottom. After seven years they
continue to thrive and be productive in the same perlite.
WATER
About 75% of orchids are epiphytes and in the wild grow clinging to tree
branches or onto rock surfaces. They derive their nourishment from the low
level of dissolved nutrients in the rain water that runs over them. They
grow so slowly that they only require and are able to tolerate about 1/4 the
fertilizer concentration that is needed by most plants. In order to provide
the full range of nutrients, the water itself must have a low background
concentration of salts. The other 25% of orchids, found mainly in the
temperate climates, are terrestrial and grow in soil. However, all orchids
respond well to hydroponic growing. The discussion of water may be broken
down into two parts:
1. total quantity of salts
2. qualitative analysis of the salts
QUANTITATION OF SALT CONTENT
The salt content of water may be measured by testing the EC. Pure water
conducts an insignificant amount of electricity and the reading will be near
zero. However when most salts are added the water will conduct electricity.
There is a direct relationship between the concentration of any particular
salt (or mixture) and the EC. An EC meter for measuring the concentration of
salts consists of a battery (replaceable), a digital readout and two wires
(electrodes) which are inserted into the solution. The amount of current
flowing between the electrodes shows up on the readout. The EC is measured
in units that are either called mhos (this is ohms (resistance) in reverse)
or as Siemen (S). They are different names for the same measurement. 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 1000 as 1000umhos or 1000uS. Most
plants use a higher concentration and it is measured in thousands called
MilliSiemans (1mS=1000uS) or mhos (1mmhos=1000umhos), in Europe, the Siemens
is the unit of measure for conductivity. In Australia conductivity is often
measured as Conductivity Factor (CF) 10CF=1mS=1mmhos.
There is another type of meter which is calibrated to read in units
called Total Dissolved Salts (TDS). This meter reads in TDS units and is
calibrated so that it will give a reading in parts per million (PPM) which
is milligrams per liter (mgm/L). However, this is misleading for each salt
varies in its ability to conduct electricity (some such as urea do not even
conduct electricity). Thus, none of the meters really give the true salt
concentration but rather, having made up and established the conductivity
reading of the fertilizer solution that you wish to use, the meters will
tell you if you have made it up correctly next time. It will also allow you
to follow the changes in concentration of the solution in pots or in a
circulating solution.
For orchids, a small hand held meter that reads from 0-1999 uS is easiest
to use but one reading in mS is useable for orchids and much better for
growing most other plants.
Modern meters compensate and correct for water temperature. This is
necessary for a low temperature significantly reduces the conductivity and
so gives a false reading. Test solutions are also readily available to check
the calibration of the meter.
Although the above description sounds very complicated once you have a
meter in your hand it all follows quite easily.
As mentioned earlier, since orchids require such a low level of
nutrition, it is important that the water supply also has a low level of
salt. Water with an EC level of under 100uS is very good and even up to 200
uS is acceptable. Certainly orchids are grown in water that is far from
ideal, but they respond much better in water with a low salt content, be it
naturally (rain water) or artificially produced, to which the appropriate
fertilizer is added.
QUALITATIVE ANALYSIS
Not only should one know the total salt content of the water supply but
also the proportions of the various salts that make up the total. All of
this information is readily available from the local water authority or
often local orchid and garden societies are able to supply their members
with this information. In some areas, the water is very hard (and alkaline),
meaning that it has a high content of salts, most often Calcium and
Magnesium in carbonate form. The further addition of these salts in the
fertilizer is not likely necessary for orchids and could be toxic.
FERTILIZER
All plants need Hydrogen, Oxygen and Carbon, as well as 12 or 14 other
nutrients. The plant derives the first three from the atmosphere through
pores in the leaves ( though oxygen is vital to the roots) and the other 12
almost entirely by the roots. Table 2 gives the salt content of the
fertilizer that we use and assumes that the natural salt content is minimal.
The problem in supplying all of the nutrients in one solution is that if
the Calcium in Calcium Nitrate, and the Sulphate in Magnesium Sulphate meet
in a concentrated solution, Calcium Sulphate will rapidly precipitate out as
a white mass at the bottom of the bucket. Hence, it is important that these
salts only come in contact when they are diluted so that this reaction is
slowed.
Thus, nutrient salts may be divided into two groups, the first containing
the Calcium (usually Calcium Nitrate), and the second all the other salts.
These salts may be put together two ways:
1. Diluting them to the appropriate EC required and then using the combined
solution.
2. Diluting the concentrated solutions of the two groups of salts by means
of an injector unit. Two Dosmatic units may be used in series and they give
accurate dilutions at varying pressures. We set ours to give a dilution of
1/100. Two Hozon units may be used in parallel but the EC at the nozzle must
be monitored as it will vary a great deal according to the water pressure.
For example, raising the end of the nozzle four or five inch (1.5 m) may
result in a decrease in the fertilizer concentration of 30 or 40 %.
pH
Perlite is neutral (i.e. pH=7), thus the acidity or alkalinity of the
fertilizer solution determines the pH of the growing environment. The pH may
be measured by a meter similar to the EC meter. It requires more frequent
calibration. The pH meter also corrects for temperature even though the
reading is only minimally affected by changes in the temperature of the
solution.
FERTILIZING
We use two parts of Calcium Nitrate by weight in one bucket and three
parts of 7-11-27 in the other bucket. The salts are weighed so that at a
dilution of 1/100, we get an EC of 600 uS at the nozzle. We fertilize/water
heavily (so that the water flows freely out of the drain holes) for five
waterings and use plain water at the
Table 2. Chemical make-up of fertilizer solution at 600uS.
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