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Thoughts on deflasking orchids and maximising growth in compots - tips from Roy Tokunaga

by Ken Jones


I was fortunate to spend some time with Roy Tokunaga (H & R Nurseries) on the Monday after the Conference and Show. Unfortunately, I was not able to attend his presentation and some of the following may be familiar to those of you who did (as I understand that he addressed many of these issues). Some years ago, Tony wrote some helpful notes on deflasking which are on the Society's website. The following adds to the helpful 'how to' advice that he provided.


While I have been deflasking orchids for more than 30 years, I did not know or appreciate the significance of some of the following. Roy told me that his flasks are pH stabilised, to increase the shelf life in the dark or stressed conditions.
By way of comparison, he advised that some of the flasks that he purchased from other vendors were in poor condition when he got back to Hawaii. He said that the flasks were 'old' and the pH was really low at less than 4.


So what does this mean and why is pH important? pH is a scale of 1-14 that measures the acidity or basic nature of an aqueous solution, where a reading of 7 is neutral. In this context, pH applies to the aqueous solutions, not bark or other media. For those of you with pools, spas or large fish ponds, you will be familiar with pH and the process of adjusting or 'buffering' to change the pH to a level that is most efficient for the chemicals, or in the case of the fish pond, for the health of the fish and plants. In more technical terms, pH is a direct measurement of the balance between acidic hydrogen ions (H+) and basic hydroxide ions (OH-). The solution can be very acidic = 0 or very basic =14. At a pH of 7, the concentrations of H+ and OH- are equal and the solution is said to be neutral. For orchids, the recommended media pH is in the range 5.8 - 6.2, that is, slightly acidic.


It is also important to differentiate between alkalinity and low pH (basic) characteristics of aqueous solutions. Alkalinity is a measure of how much acid it takes to lower pH below a certain level (the acid-buffering capacity). Alkalinity arises from the presence of ions that affect acid-buffering capacity including bicarbonates of sodium, calcium, magnesium, and to a lesser extent, sodium and calcium carbonate. By now, you're probably wondering why this is relevant as it seems very complex. I can hear you saying, "…but I just want to grow my orchids!" Alkalinity is important because it is more critical to managing the pH of your media than the pH of your water. While the rainwater which I use to water the majority of our orchids is pH 7.8 (I suspect because it is stored in concrete tanks which would leach into the water), the alkalinity (according to the test strips for our spa) is about 25-30 parts per million. This potentially has a significantly adverse effect on media pH as the water is both basic and alkaline, and as you will see from the following, the capacity of plants to absorb critical elements necessary for vigorous growth may be compromised.


The critical thing about pH for plant growth is that if it is too low (acidic) or too high (basic), plants experience difficulty taking up nutrient. For example, pH values of >8 limit the availability of iron (Fe), Manganese (Mn), Boron (B), Copper (Cu) and Zinc ( Zn), while values <5.5 limit availability of Potassium (P), Calcium (Ca), Magnesium (Mg) and Molybdenum (Mo). This list contains most of the essential elements with the exception of Nitrogen (N) and Phosphorous (P) which are less susceptible to variations in pH. What this means in practice is that we should be paying more attention to pH, both in the fertilisers we use and the effect that they have on our media. While it commonly accepted that some orchids, eg Paphiopedilums prefer media that is more basic pH (for many of them, the natural habitat is over limestone), all orchids are going to be more vigorous and make better use of the nutrients that we provide if the pH is closer to neutral. Clearly, those which in the natural habitat grow in moss beds will be highly susceptible to high or low pH. Roy stressed during his lectures that in his experience, calcium is just as important for flowering as potassium and as important as nitrogen for new growth. It is also critical to the development of immune response in plants against fungus and bacteria. He recommends a pH of 5.6 for flask media. Some that I have tested recently were 3.6 - 4.4, that is quite strongly acidic while the plants were literally starving!


Based on the limited research of this topic undertaken for this article and seeing the improvement in my orchids after Roy's advice about application of dolomite lime (in just a few weeks), I have realised just how critical pH and alkalinity are to vigorous plant growth and now know that that I need to pay much more attention to these factors in future. Roy recommended a series of articles by Bill Argo of Blackmore Company in USA which I found on the St Augustine Orchid Society webpage at http://www.staugorchidsociety.org/culturewater.htm If you are at all interested in this topic (and if you are serious about growing your orchids well, you should be!), I can thoroughly recommend this series of articles on pH management and plant nutrition. While scientific, his articles were written for orchid growers and use understandable explanations for complex concepts.


Calcium is also important for flowering. It is absorbed by the roots and transported in the xylem at the time of flowering (note, it cannot be stored in the bulbs or roots for future use). The xylem is one of two types of transport tissue in vascular plants and is derived from the Greek word xylon, meaning "wood". The best-known xylem tissue is wood, though it is found throughout the plant. While its basic function is to transport water, it also transports some nutrients through the plant, particularly Calcium. Calcium is highly immobile, and moves through the xylem with transpiration stream. If the humidity is too high or the stomatas are closed, Calcium cannot be transported from the roots to the growing leaves. Calcium needs to be incorporated into the cell walls and membranes at the time they are synthesised.


So what did Roy mean by the term pH stabilised, and what is the significance of this? In his experience, the pH of media in a flask tends to drop to less than 4 within 5 months of sowing. From what we know about the impact of pH on nutrient uptake, this tells us that the plants are literally starving. Remember, there is only a limited supply of nutrient with many plantlets competing for it, and pH at this level is such that any residual P, Ca, Mg and Mo are not able to be absorbed by the plantlets. What Roy has discovered over time is that many commercial flasks are calcium deficient, particularly if they are 'old' and low on nutrient. This is even more accentuated if the laboratory did not pH stabilise prior to sowing. To keep it above 4.5, he says that it is necessary to buffer before sowing, and for the final months, grow the flasks under bright light (up to 2000 ft. candles for bright light species and hybrids) to ensure that plants are healthy. This is particularly relevant to all of us as the flasks imported for sale at the conference were in the dark for up to two weeks prior to being offered for sale. Therefore, it makes sense to get them into bright light as soon as possible after purchase and to deflask while the plantlets are actively growing.


When deflasking, it is important to use media that is pH adjusted to 6. This can be simply done by adding Dolomite lime which provides both calcium and magnesium to the deflasked plantlets. Roy recommends immediate fertiliser application of calcium nitrate [5Ca(NO3)2.NH4NO3.10H2OC] at the rate of 1 gm/l (1/4 teaspoon per litre), and to avoid fertilisers containing ammonia (NH4) for one to two months (in this regard, you should be aware some high nitrogen fertilisers contain ammonia, or are sourced from ammonia). This regime helps avoid black rot within the first month of transplanting (I will provide further feedback on this in the next newsletter as I have now used this method on more than 100 flasks).


Roy chose to replate the flasks he took back to Hawaii (he refers to them as "Dead on Arrival") because while the plants may appear to be alive, they cannot survive out of the flask. He said that it had taken him 30 years to figure out how to maximise deflasking survival. He told me that on replating, 10 % of the plants died immediately reinforcing his assessment that they could not have survived deflasking into compots.


As members are aware, we are trying to save a number of the H & R mother flasks that would otherwise have been destroyed. Roy's advice was to grow them for one month in the quarantine glasshouse and they will be ready for deflasking. All his flasks are dated and will be OK for up to 6 months in their crowded condition. He has tested some up to 12 months but found that losses started after about 8 months.


As it will not be possible to replate them (I cannot move them out of the quarantine glasshouse), Roy recommended that we use the method that they employ at the nursery for their own plants. As the expense of replating in US is substantial due to labour costs, they deflask from the mother flasks into trays filled with sphagnum moss onto which dolomite lime has been sprinkled. He says that they have very good results from this approach. Given the limited space available in the quarantine glasshouse, and his advice, I will do the same and advise the results in a future newsletter.