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Orchid culture - theory and practice part 1


Anyone who deals intensively with the growth of their orchids will recognize that there have been constant ups and downs in orchid culture over the years. So there were phases in which my orchids grew well and bloomed, but then suddenly and without a recognizable reason, there was no longer any growth. Why could that have been?

New growing media or fertilizers are constantly being advertised, many of which I have tried. What substrates did my orchids not have to root through - meranti, coconut fibers, rock wool, lava rock, perlite! I've even planted my orchids in hydro and semi-hydro culture on clay pebbles.

The first year in the respective planting material always looked like a "success story", in the second year of cultivation the planting material was often questioned and then the plant urgently had to be repotted because growth disorders were evident. If orchids suffer damage to roots, bulbs or leaves due to cultivation mistakes, the new shoots will no longer grow as vigorously in the following year and flowering will probably not occur. This is followed by a laborious nurturing of these plants.

The basics for a successful orchid culture are known in theory - is it just the practical implementation that is lacking?

The temperature and the light are determined by the weather and only have to be taken into account in the respective culture area and adapted to the orchids to be cultivated.

We know from their natural location that most orchids are often exposed to rain and fog for hours. Depending on the season, orchids also have to survive longer dry periods without any precipitation.

The roots of the orchids and here in particular the epiphytes have adapted well to this way of life. They are surrounded by a layer of dead cells (velamen). When these cells are dry, they appear silvery except for the active root tip. As soon as it rains, they soak up water like a sponge and turn green. Now they temporarily serve as a water reservoir for the plant until the sun and air movement allow the roots to dry out again. Without exception, pure water evaporates - the residual salts from the rainwater or irrigation water remain.

If such a root grows in moist humus or even in water, the protective velamen layer is regressed and becomes susceptible to excessive salt concentrations in the substrate.

Could my failures be related to the fact that I haven't given enough attention to how the root works and its special requirements?



The prevailing opinion on fertilization is that you should provide plants with all the necessary nutrients. The orchid takes the elements needed for growth. There is hardly any information about unused "nutritional salts", which may also have a toxic effect.

Very little is known about the correct ratio of nutrients to each other (e.g. nitrogen-phosphorus-potassium). Calcium and magnesium are found in very few fertilizer solutions, or only in small amounts, although both nutrients are essential for plants. There is also more speculation about the level of the maximum salt load from the fertilizer than there is reliable knowledge. However, we know from their natural location that most orchids grow in a rather low-salt substrate.

If orchids are grown in the retort (in vitro), the salt content in the culture medium is often around 2000 µS.

How is this high discrepancy regarding the salt content in the orchid culture to be assessed and can we really successfully cultivate all orchids in our culture areas according to a uniform culture scheme?

Although in autumn 2015 the outside growing conditions were good due to the weather in my greenhouse, once again the plant and root growth was not good and only a few orchids wanted to flower. The reasons for this had to be found now. Too high a salt content in the substrate? I then asked myself how to measure the salt content in the substrate.

I had read about a ThruFlow method on the Internet: 500 ml of rainwater (35 µS) are allowed to run slowly through the substrate, the water that has run through is collected and the salt content is measured. Result = 180 µS

After the measurement, I noticed that I had overlooked the fact that this measurement method should only be used four hours after the actual casting process. The next weekend I watered my orchids with rainwater and then repeated the above method 4 hours later. Result = 410 µS

At the same time, I placed an orchid in bark substrate in rainwater up to the top edge of the pot:

Measurement result after 1 hour = 280 µS

Result after 2 hours = 390 µS

Result after 4 hours = 490 µS

Here I was faced with a puzzle. How could it be that I was shown such different measurement results?

In order to solve the riddle, I searched the orchid literature for solutions on how to measure the salt content in the orchid substrate. Finally, I found what I was looking for in G. Bomba's book "Orchids - Origin and Care": Take equal parts substrate and rainwater, e.g. 100 ml each, put everything in a sealable container and shake it for two hours. Incidentally, this method is also used in the agricultural testing and research institute (LUFA in Germany) for soil samples.

The result of my measurements was shocking: 2100 µS - no wonder that there was hardly any plant or root growth to be seen. Residual salts from the regular application of fertilizers obviously settled on the bark substrate, which had not been dissolved or washed out with the pure rainwater application in the meantime. Only intensive shaking with the method described dissolves the residual salts and leads to the high salt content results.

Looking back, I thought about which fertilizers had been used in 2015.

As a basic fertilizer, 0.4 g / l of Scotts Exel CalMag 15-5-15-5-2 and similar fertilizers was added to the rainwater (~500 µS).

However, the Exel fertilizer creates a low pH value. To compensate for this, I added approx. 25% pond water (high pH value) to the rather acidic rainwater in order to achieve a tolerable pH value of around 6.0.

A laboratory analysis of my pond water (August 2015) yielded the following results:























< 1,0


> 1,2










As an additional fertilizer I had regularly watered my orchids with "chlorophyll water" - let me briefly explain what this is all about.

Rather coincidentally, I had read on the Internet that in an allotment garden with ecological management, vegetable waste and wild herbs were chopped up with water in a mixer and then this green water was returned to the garden soil with the chopped residue. Couldn't this procedure also be applied to orchids?

When I started with the orchid hobby many decades ago and salt fertilizer for orchid cultivation was still unimaginable, we made plant manure from stinging nettle, horsetail, dandelion etc. and watered our orchids with it. In addition to the often bestial stench, we also had to struggle with rot again and again.

My idea now was to chop fresh herbs (see above) with the blender, filter them and fertilize the orchids with this green (chlorophyll) water. All ingredients of the plant used are thus immediately available to the orchids. The chlorophyll juice has a salinity between 1600 and 2000 µS and was diluted with rain water in a ratio of 1:10.

From spring 2015 I used this chlorophyll juice as a foliar fertilizer - the effect was visible for a short time: almost all orchids with softer leaves got a dark green color and looked very vital.

The following summer I used this chlorophyll juice in addition to the fertilizer mentioned above, also over the substrate. The salinity then increased to values of 700-800 µS.

I had the chlorophyll juice, which usually consisted of nettles and dandelion, tested in the laboratory for its ingredients:


NH4 / NO3






















19 + 28








> 2




I was amazed at the relatively low nitrogen content in the laboratory analysis. When I asked, the laboratory informed me that experience has shown that such plant juices contain a high content of amino acids, which, however, could only be analyzed at great expense. These amino acids can be absorbed directly by plants and thus produce the positive effect on orchids.

If you want to test the effect of plant extracts, but the manufacturing effort is too high, I recommend using ready-made nettle extract or horsetail extract (e.g. from Neudorff (Germany), or similar).



But back to the actual question: How could such a high level of salt in the plant material arise?

When researching the cause, it occurred to me that the battery in my conductivity meter was replaced in the summer. Shortly before the replacement, the device alternately displays no value or values that later turned out to be incorrect values. With regard to these incorrect values, I then dosed the fertilizer - obviously far beyond the beneficial level!?!

But that could not be the sole cause of the high salt content in the substrate!

In the introduction to this article I described the conditions of orchids in their natural habitat. There is often hours of heavy rain there.



In my culture, the "flushing of the plant material" was carried out with pure rainwater in a spraying process. Obviously, this minimal amount of water is not enough to wash out salt residues from the plant matter. In the orchid literature, there is always talk of vigorous flushing of the plant material.

While researching on the Internet, I became aware of a product that advertises making old salt residues in the substrate available to plants again: FloraKleen (new name = FlashClean).

This product is used in plant production, mainly in hydro culture, to make "used" expanded clay reusable for subsequent cultures. But even in conventional substrates, no harmful salts should be deposited in the plant material with regular use.

The ingredients of this product are a balanced mixture of mineral salts and chelates. With the recommended dosage of 1 ml / 1 liter of irrigation water, the conductance increases by 70 µS.



Armed with these new findings, all orchids were once again repotted in fresh substrate in winter 2015 / spring 2016. I tested the pine bark used from three different sources using the "shake method": The salt content was 320 µS, 480 µS and 650 µS!

To reduce the high salt levels, I soaked the bark in rainwater once or twice for a day at a time before using it as a planting material.

In the following cultivation period (summer 2016), the orchids in the greenhouse and on the windowsill were alternately supplied with different fertilizers around 550 µS and pure rainwater with Flora Kleen via the substrate.

The Phalaenopsis hybrids on the windowsill showed very good leaf and root growth after a short time, which was rewarded with an above-average bloom at the end of summer.

In the greenhouse, too, I had the impression that rapid growth was visible, especially after applying rainwater with FloraKleen.

In addition to the weekly waterings, depending on the weather, the orchids were sprayed with the chlorophyll water described above as a foliar fertilizer. Most of the plants looked and still look very vital afterwards.

If you take a closer look, you can discover fine root hairs on some orchid roots (see illustrations), which I had never seen in previous years.




So once again everything points to a "success story", which is now not only visible in the growth of the plants, but also in the growth of the roots. Whether this will last, however, will only become clear in the course of the next year.

As a precaution, I measured the salt content of the plant material again in autumn and determined the value of approx. 700 µS using the shaking method. At the same time, I put the plant substance directly into water, stirred it and then also got a value of around 700 µS. The Flora Kleen has obviously worked and there are no longer any difficultly soluble residual salts in the plant material.

In any case, this winter my orchids will only be watered with rainwater and occasionally with rainwater and Flora Kleen so that the residual salts in the plant material can be reduced even more or no longer accumulate.

A light foliar fertilization and chlorophyll water will provide those orchids with nutrients that also or especially grow in the winter months


sequel follows





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