Orchid Culture: Nutrition

In nature orchid seeds can only germinate and develop with the symbiotic relationship between plant and beneficial microbes. Knudsen discovered that sugars were the necessary byproduct of this relationship and then invented a formula to bypass the need for microbes. Thus began the raising of orchids in the sterile environment of a flask.

Do orchids absorb organic compounds? At the University we were told plants could only absorb inorganic molecules. Are orchids really absorbing organic compounds? Can all plants absorb organic compounds? I believe that orchids sometimes don't have a choice. They can't help but absorb some of what is placed on their plant parts. For example ethylene is an organic compound and probably passes easily through the stomatas of orchids and is found to cause bud drop if concentrations get too high. Yes, it's a smaller molecule than most organic compounds so it makes sense that it would have an easier time moving into the plant. One could reason that many organic compounds are much larger than a simple gas and thus have a greater difficulty entering the orchid plant.

It also stands to reason that inorganic ions would have a very easy time passing into an orchid plant and thus chemical fertilizers would move very quickly into the plant. So what is the best fertilizer or nutrients that you could add to your orchid plants to make them grow and bloom? I don't think that there is a single orchid fertilizer on the market that is totally complete and perfectly balanced to fulfill the nutritional needs of an orchid, although they come very close. And of the ones that seem to come very close, they seem, in my opinion, to be of an organic base.

Remember the orchid seedling's immediate need for a symbiotic relationship with beneficial microbes? Is it possible that perhaps the need persists throughout its entire life? Organic-based nutrients can provide a sizable addition of compounds that beneficial microbes thrive on. The problem is that sometimes if improper conditions exist, organic compounds can also be a source of food for the potentially pathogenic, leading to rising populations and decay.

Generally the nitrogen source becomes the more important consideration in selecting the base for your organic source. I use the term "base", because it may be necessary for you to use other components to create a better balance of nutrients. Of the many different organic sources of nitrogen, we have discovered that feather meal works well with our orchids. Feather meal is relatively slow to decompose and thus provides a long lasting source and also doesn't seem to lead to large rises in the population of pathogenic microbes, especially if it is inoculated with beneficial bacteria and fungi.

The source of phosphorus has been simplified by research, showing that most forms of phosphorus are detrimental to beneficial microbes. Their findings indicate that the molecular relationship of dicalcium phosphate seems to be of the harmless form. Used generally as food supplements in chicken feed as well as in vitamin formulations, dicalcium phosphate is also the form we use for our orchids. It comes in granulated form that we mix into our feather meal base.

The third nutrient consideration is potash. Potash is a highly soluble, but vital component that easily leaches out of solid fertilizer applications long before the other components are used. Liquid sources of potash can be sprayed in the form of potash soaps, but we have found Greensand to be a long-term source. Actually, it may be too long-term because it lasts for about three years. Greensand is mined from the beds of ancient sea life and not only provides potash, but just about every micronutrient.

Micronutrients can be pretty tricky since they are needed in such small amounts as the name implies. Organic sources contain micronutrients in varying amounts; The ocean, where all the waters eventually run is know to be a rich source of micronutrients. So Greensand and seaweed are basically the two sources we use for those reasons.

But what about the proportion of each component? Fertilizer is generally rated by the amount of the three "NPK" components. The NPK rating is a reflection of what is immediately available to the plant. Does this make chemical fertilizers or inorganics really potent and of high value? Well, immediately they do provide high quantities of the three basic components because they are soluble salts. With organics much is not immediately available and this results in a low "NPK" rating. It doesn't mean that is all you get, because most of it is stuck along long carbon chains and need the help of microbes to unleash them. So with organics there is a lot more behind the NPK rating.

Formulations seem to vary, but for starters, we try to work toward an even amount across the board. Then we modulate formulations based on the developmental stage of the plants, the type of growth we wish to promote, and the seasonal fluctuations in light and temperature that affect the release of certain nutrients. So there doesn't seem to be one magic formula. By experimenting and adjusting the components you will be able to detect visible signs of greater or lesser needs.

There are many choices of nutrients both in inorganic and organic form. Both types are available in commercial and household quantities and some individuals even make their own through composting methods. When evaluating the total effect of our fertilizer practices we opt for the somewhat labor intensive method of topdressing our plants with solid organic fertilizers. It not only eliminates pollutants being added to the ground water but also seems to produce better quality plants.