Orchid culture - theory and practice part 3

As a conclusion from the first two parts of my essay on the subject of orchid cultivation, I found that "salt formation problems" in the different substrates have repeatedly occurred in my cultivation. Even the regular rinsing of the planting material with rainwater did not lead to a reduction in the high salt content in the planting material and therefore not to an improvement in the orchid culture.

I then looked for an alternative to mineral fertilizer salts and finally found it in compost tea (part 2). To do this, worm castings are dissolved in water. I have been watering my orchids regularly over the substrate with this compost extract for the past year and a half. In addition, the plants were supplied with a foliar fertilizer weekly. Since the beginning of 2018, the mineral content of the fertilizer solution has been drastically reduced, the conductivity hardly exceeds 200 µS.

I am satisfied with the growth and flower production of many of my orchids today, but there is still room for improvement. My orchid stock consists of 70% Paphiopedilum natural forms, the rest consists of natural forms of the genera Cattleya, Phalaenopsis, Oncidium, Odontoglossum etc.

A growth-related fertilization can hardly be realized, since many orchid species have different growth rates. While Cattleya have formed their bulbs in autumn and hardly need any fertilizer, the Laelia (Cattl.) purpurata plants, for example, are just beginning to grow. There are also summer and winter growers in the Phalaenopsis and Paphiopedilum species. So a sufficient and complementary "fertilization" had to be found for the whole year in addition to the compost tea.

I have been repeatedly asked by orchid friends whether the production of the compost tea is not very time-consuming. Yes, absolutely. If you also only cultivate a few orchids on the windowsill in your apartment, you will not make this effort. In addition, the extract must be used immediately after production, as it can rot after a few days and thus become unusable as an orchid fertilizer.

This question prompted me to look for alternatives to the self-made worm humus extract.

I heard about a product based on compost made from grape pomace from an organic farming consultant. Wine pomace is the residue from pressing that occurs during the production of wine. This pressing residue is first fermented in a complex process, then oxidized and finally extracted.

During fermentation, the raw material (here pomace) is decomposed by microbial processes in the absence of air (anaerobic). This results in enzymes, amino acids, vitamins and ultimately also mineral salts, which can then be absorbed and utilized directly or as press juice from plants as “fertilizer”.

Fermentation products are already known to us in orchid culture - e.g. Vitanal, Waldleben, KE extract. When dosing these agents, however, you have to take into account the very low pH value and then adjust the pH value to around pH 6.0 after adding the agents to the irrigation water.

In order to raise the low pH value of the fermented pomace in the production process, the pressing residue is oxidized in a next step. This process largely corresponds to composting. Air is added to the pomace through repeated turning, the compost matures and the pH value rises into the neutral range.

This finished compost from grape marc is used in organic farming as a certified organic fertilizer. So that this product can be used by a larger group of customers and thus also by us for the cultivation of orchids, water is added to the compost in a further work step and enriched with oxygen (extraction). In a process lasting several months, a valuable liquid “fertilizer” is produced from grape pomace humus, which can be kept for at least a year.

If you compare worm humus with grape pomace humus in terms of its ingredients, you will find that comparable levels of nitrogen (3-4%), phosphorus (1-3%) and potassium (2-4%) are present in both products. Only a fraction of these nutrients can then be found in the aqueous solutions from these composts. That is why these products are also marketed as plant additives.

For orchid culture, this could mean that an easy-to-use option for organic nutrition has been found with the liquid pomace humus. These products made from wine marc are manufactured in Germany by the company BioVin and are also sold in liter bottles under the name BlütoVin or FertiCult Orchideendünger.

If you search for the name BioVin on the Internet, you will notice a company in Austria with the same name. There is a link to the Tyrolean Orchid Association. BioVin has been used successfully in orchid culture for 15 years.

In parallel to these experiments, I am always concerned with the question: How do the orchids feed themselves in their natural habitat? The plants in the jungle are often much larger than in our culture.

A thesis from plant research states that the growth potential of plants depends heavily on their nitrogen supply. Nitrogen is the engine of nutrient dynamics. Without it, the other available main nutrients and trace elements can only be insufficiently utilized. For this reason, special attention should be paid to the nitrogen and the type of nitrogen.

In Canada, a team of researchers from McGill University in Montreal found in a biosphere reserve in British Columbia that large amounts of nitrogen compounds are produced by cyanobacteria (blue-green algae) in the crowns of old trees, which the forest benefits from as fertilizer. Blue-green algae are able to convert the molecular nitrogen in the air into organic compounds. These blue-green algae settle mainly in the mosses that grow on trees. The older the trees are, the greater the moss cover and thus also the colonization with blue-green algae.

The next time it rains, these nitrogen compounds are washed out and are available to the trees or other plants (epiphytes) in the forest.

In another study, German researchers examined the contribution of crytogam layers, which can fix large amounts of carbon dioxide and oxygen. About 30% of the world's land areas are covered by crytogamous layers. Crytogams are creatures that are capable of photosynthesis but do not form flowers. These include mosses, lichens, algae, fungi and the already mentioned cyanobacteria. With the help of light, they bind significant amounts of nitrogen from the atmosphere. This type of nitrogen fixation produces ammonium that can be used immediately by plants.

A large part of the orchids in the primeval forests grow where mosses and lichens are present. Obviously, orchids can benefit from the nitrogen fixation just described. Furthermore, orchids in their natural habitat seem to grow particularly where fallen leaves have accumulated. In the constantly high humidity and heat, this foliage is quickly broken down as organic matter and broken down into its mineral components (humus) and is then available to the plants as food.

From previous agricultural research we know that nitrogen is taken up by plants in the form of nitrate and ammonium. Nitrogen is generally taken up by the roots, but the leaves can also take up nitrogen.

Nitrate enters the plant with the soil water (passive uptake). The plant hardly needs any energy for this type of absorption, but it cannot control the amount of nitrate absorbed. If the intake is greater than the need, thin cell walls develop as a result, which can affect the stability of the plant and thus possibly lead to diseases or pest infestation.

In contrast, the plant has to expend more energy to absorb ammonium. This so-called active uptake ensures that the plant only absorbs as much nitrogen as it needs.

Due to the high use of mineral or animal fertilizers in agriculture, reports of high levels of nitrate in our drinking water are increasing. Alternatives to the previously used fertilizers are being sought through new research contracts. It was found that plants not only absorb ammonium and nitrates as nitrogen sources, but that urea and amino acids can also be directly absorbed and utilized by the plants. The advantages and disadvantages of urea and amino acids for the nutrition of our orchids are briefly outlined below.

In recent years, urea has been experimented with in agriculture as a source of nitrogen. If urea is added to the arable soil, so-called nitrification begins: bacteria convert urea first into ammonium and then later into nitrate. In order to delay this conversion process, both urea and ammonium have been provided with an organic coating that is only slowly broken down by soil bacteria. The goal is to ensure the flow of nitrogen for a longer period of time and to supply the crops with different sources of nitrogen. Ultimately, as little excess nitrate as possible should get into the groundwater.

Due to the unpredictable time delay in the flow of nitrogen, urea has rarely been used as an orchid fertilizer. If you add urea to a fertilizer solution, the conductance does not increase. However, during the subsequent conversion of the urea into ammonium and nitrate, the conductance increases and with it the salt content in the orchid substrate.

Irrespective of these possible disadvantages, in the past some well-known orchid farms and collections used urea as the sole source of nitrogen with very good results. It is known from in vitro culture that some types of orchids germinate and grow better on ammonium and other types on nitrate as a nitrogen fertilizer. There are also successful offspring that have been raised on culture media with only urea as the nitrogen source.

The use of urea in orchid nutrition will continue to be controversial.

What remains is the use of amino acids as a source of nitrogen for our orchids. If you read the data sheet of Vitanal and similar fermentation products, amino acids are at the top of the list of ingredients. Some of my orchid friends are convinced of the positive effects of these plant additives. However, there are also studies with parallel tests on orchids with such products (with and without fermentation products) with the result that no improvement in growth could be determined. However, if the plants have already been sufficiently supplied with nitrogen in these experiments, a small additional proportion of amino acids from these "fertilizers" should not actually result in any improvements.

During further research on the subject of "amino acids" I became aware of an organic fertilizer made from sugar beet - vinasse.

So-called factory molasses remains in the sugar factory after the white sugar has crystallized. This molasses is used as animal feed because of its high nutrient content, but is also processed as a raw material by the yeast and alcohol industries. There the molasses is cleaned, acidified and enriched with bacterial strains. Alcohol is produced during the subsequent fermentation, and the molasses residue, which is then largely desugared, goes back to the animal feed industry or to agriculture under the trade name Vinasse.

The vinasse has a balanced proportion of organically bound minerals, the nitrogen consists mainly of amino acids and the pH is around 6.0. This seems to be an organic fertilizer with all the necessary nutrients for orchid culture.

In addition to the humus extract, I carefully fertilized my orchids with vinasse both over the substrate and over the leaf. The first positive signs could be seen. In the coming vegetation period, the right amount of fertilizer still needs to be tested.

In my experiments with the culture of orchids without mineral fertilizers, fine root hairs became visible on the roots outside of the plant material in some coelogyna and lycasta. These disappear immediately when mineral fertilizer salts are used.

In the next few years it will have to be seen whether the cultivation method I have chosen can bring better results in the cultivation of orchids in my greenhouse - initial successes are visible.

If you were expecting complete instructions for cultivating your orchids at the end of the article, I have to disappoint you. But that is mainly due to my "thirst for research" - as soon as I seem to have solved a problem, new ideas on how I can improve the culture are already there.

sequel follows