by Jerry Sellers
Although it is common practice to call them Orchid food, fertilizers are not really food for our Orchids. Using water, carbon dioxide and energy from the sun, Orchids actually make their own food. So fertilizers can best be called Orchid nutrients. Plant nutritionists have identified seventeen (17) elements essential to Orchid growth. Because Orchids require them in larger quantities for maximum growth, Nitrogen (N), Phosphorus (P) and Potassium (K) are referred to as macro nutrients. The other elements needed in smaller quantities, such as Calcium (Ca), Iron (Fe), Copper (Cu), and Zinc (Z), are referred to as micro nutrients or trace elements.
All commercial Orchid fertilizers are labeled with three numbers, such as 10-20-30. These three numbers are the percentage by weight of the primary nutrient components of Nitrogen (N), Phosphorous or phosphates (P) and Potassium or potash (K) in the fertilizer.
Nitrogen is important for leaf and stem growth and provides the rich green color in leaves.
Phosphorous provides for root and flower development.
Potassium helps build Orchid tissue and aids in the production of vital chlorophyll.
A fertilizer is said to be complete when it contains N, P, and K. Fertilizers are said to be balanced when they have the same ratio of N, P, and K. Examples of commonly used Orchid fertilizers ratios are 20-20-20, 30-10-10, and 10-10-10. When comparing fertilizers, one is told to check the ratio of the three numbers to each other. How many times have you heard "20-20-20 is exactly the same as 10-10-10, just use less of it"?. True, each has a ratio of 1 to 1 to 1; However, they are exactly the same in ratio only! As these ratio numbers are percentage expressions of the primary nutrient components, a hobbyist should compute the amount of each fertilizer needed to obtain the ideal concentration of the nutrient. For periodic feedings, 150 to 200 parts per million (PPM) of N is excellent. To obtain the desired concentration of Nitrogen, One could use a chart. But the actual calculations are quite easy. The same calculation can be used for obtaining the desired concentration of the other nutrient components. Using the given rule that one ounce of fertilizer dissolved in 100 gallons of water yields 75 (PPM) of fertilizer at delivery. Therefore, to decide how many ounces of 10-10-10 to add to 100 gallons of water to obtain 200 PPM available Nitrogen at delivery, multiply the decimal equivalent of the 10% N component in the formula, 0.10 x 75 PPM = 7.5 PPM; then 200 PPM divided by 7.5 PPM means that 26.7 ounces of the formula would be needed. For the 20-20-20 product, the calculation would be .20 x 75PPM=15 PPM; then 200PPM/15PPM =13.3 ounces. Of course if you use a five gallon bucket of water instead of a 100 gallon bucket, divide the required product by 20 ( 5 gallons is 1/20 of 100), ie 13.3/20 = .665 ounces, or by 100 if you are using a one gallon bucket, which would be 13.3/100=0.133 ounces. If you use a siphoning system, such as 15:1 or 16:1, simply adjust the amount of the fertilizer to 3/4 of the amount calculated for 100 gallons for the concentrate. The concentrate is mixed 1 part concentrate to 15 or 16 parts water, resulting in 75 to 80 gallons of mixed nutrient water at delivery.
So, the actual amounts needed are different depending on which formulation is used. The old "one tablespoon per gallon" recommendation is not really usuable. Now that you have figured out the proper concentration, you need to check the analysis data on the fertilizer container to determine the true available N at delivery. Review the data information, discounting any part of the nitrogen availability that comes from urea. It can take up to a year break down Urea . By that time, the Urea is well out of your potting media, and totally unavailable to your Orchids.. So if urea constitutes 10% of the Nitrogen source in the 20%-20%-20% formula, then 50% of the Nitrogen is unavailable to the plant ( 10/20=50%), so you need to double the amount of fertilizer to get the proper amount of fertilizer to your plant. Which means doubling all the other components. Now we are entering into an area for another article called "nutrient antagonism's". Wherein the excess of one nutrient reduces the uptake of another. As an example too high concentration of Nitrogen has been proven to inhibit an Orchid's ability to absorb and use Potassium (K). The lack of K can be seen in leggy, weak stemmed plants, which lack the strength to hold up their leaves. The easiest way around this dilemma is to use Non urea fertilizers. These Non Urea based fertilizers provide 100% immediately available nitrogen, which the urea based fertilizers do not.
While looking at the data information on the fertilizer container, look for the micronutrient components. Many of the current Orchid fertilizers do not have any micro nutrients in their formula. The lack of micro nutrients is not a problem for the terrestrial plants, as the micro nutrients can be obtained from the soil. In soilless conditions, in which most Orchids are grown, micronutrient deficiencies can and do become a problem. The micro nutrients provide strength for the new growth and support for the flowers
The fertilizer formula should match the potting medium. Use 20-10-20 with coconut chips, tree fern, charcoal, or various inorganic aggregates, but use 30-10-10 (urea based), or 20-10-20 (non urea) with fir bark. For bloom boosting, use 6-30-30 for better blooming. This formula adds more K to provide plant strength to hold up the additional flowers. Many formulae do not provide the needed strength nutrients. You get a better blooming, but the flowers droop.
Slow release fertilizers release nutrients (make them available to the Orchid) over an extended period. Cottonseed meal, blood meal bone meal and fish emulsion are examples of organic fertilizers. These contain relatively low concentrations of actual nutrients and must be used in larger quantities. Most Orchid media can not readily accommodate Slow release fertilizers, because the granules are washed through the potting media before being completely dissolved. They do find some use in fine medias, which prevent the washing through problem.
Remember well, fertilizers are chemical salts, much like the familiar table salt. As a chemical salt, fertilizers will absorb water from their surroundings. Just leave a fertilizer container open for a few days to see this statement in action. So if tender Orchid roots grow close to the fertilizer granules or fertilizer residue, water will be drawn from the roots. The cells in the roots will begin to dehydrate or "bum." Frequent clear water rinses will keep the residue to a minimum. If the clear water rinses, do not wash away the residue, then re potting is in order.
The best rule of thumb is to under fertilize, rather than over fertilize. Orchids in the wild do not get all that much to "eat", and they survive well.
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