A Brief Summary of an Older Study on Nutrition of Dendrobiums

Orchids, we know, are a very old family of plants – several million years old! During all those years, they have needed nourishment. Some of that comes from the places on which the orchids grow, some comes with wind and rain, some is provided by certain fungi called micorrhizae. Most orchids have evolved in their respective habitats according to what food was and is available there. Now people come, remove the plants from their natural growing environments and try to grow the poor things in more or less artificial environments.

Scientists are mostly people who try to figure things out. Some scientists are even trying to figure out what food orchids really need. In the July 1966 AOS Bulletin, (yes- also very old), there is a lengthy article written by S.S. Chin from the Rubber Research Institute of Malaya about the "Effects of Major Nutrient Deficiencies in Dendrobium phalaenopsis Hybrids".

Here, I will present a brief overview of this paper and let you draw your own conclusions.

The experiments were started in 1961 and 24 Dendrobium phalaenopsis hybrid seedlings were used. At the starting point, the plants were 2 ¾ years old; they were washed clean, then placed in amber coloured glass bottles. By various means the roots were positioned so that most of them, except the top one cm were submersed in the fertilizing solutions, which were replaced every two weeks. After 9 ½ months, the experiment was terminated when one control plant was ready to flower and several test plants were near death. In each group, there were three plants with three pseudobulbs each at the beginning.

It is interesting that for all groups except # 2 (-N), the pH value of the solution was lowered substantially during each 2-week period – no nitrogen, no root activity, no pH change!

Observations on leaves showed that minus K, minus P, minus Mg and minus Ca had dropped their leaves early on. Plants growing in -S had as many leaves as the control group. Observations on roots showed that in -N solutions, the plants had developed more vigorous root growth than the control group. Because there may have been sufficient sulphur in the tap water used, the -S plants did not show any particular effects. However, the final, total weight of the control plants far exceeded the weight of any of the test groups.

The plants were then dried and the data from the chemical analysis showed severe deficiencies of nitrogen, phosphorus, potassium and magnesium. The -N plants had absorbed more potassium and calcium, the -P and -Mg plants had absorbed larger amounts of nitrogen and the -Mg plants had also absorbed more potassium.

In summary, this study confirms that these Dendrobium hybrids require all the major nutrients (potassium, phosphorus, magnesium, calcium and nitrogen- in this order!) for vigorous growth. Plants grown without potassium had a dry weight reduction by over 5 ½ times as compared with the control group; one can assume that this mineral is of great importance to Dendrobiums. Lack of phosphates reduced the weight by nearly 5 times, lack of magnesium by 4 times while lack of nitrogen showed a less significant effect.

Now if any of you want to continue this line of experiments, go for it! The world is waiting for your publications. The orchids are waiting for their proper fertilizers – or should we just put them all back to where they used to be, long ago and far away?

Ingrid Schmidt-Ostrander - Canadian Orchid Congress