PH (GENERAL): Of Potting Mix

Culture Orchid Doctor

by Robert M. [Bert] Hamilton (Compiler)

Originally published in The Orchid Doctor in 1980 and 1988

Posted by Sys Admin about 4 years ago.

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Experiments show that if a recommended medium is chosen the initial pH should cause no concern. Hort. revs. 1983-195
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PH (General) Comments
PH (GENERAL): Adjustment How to bring it down to normal: do not use a sodium salt; the simplest thing is to use dilute phosphoric acid, at a few drops per gallon of water. A78-698 0
PH (GENERAL): Adjustment with Dolomite Limestone If paphlopedilums are growing in a medium of 6.3 or lower a light top dressing is recommended; if pH is 7.6 or more, repot the plant. A80-229 0
PH (GENERAL): And Acidity For results of tests, soil chemistry data, chemicals, availability chart of nutrients relative to a situation, refer to AU85(1)-10 0
PH (GENERAL): Buffering Most organic media have a high cation exchange and they buffer against nutrient and pH levels; for water, best growth follows the use of a pH level of 6 to 7. A85-1435 0
PH (GENERAL): Characteristics What pH is; its effects; the ways to change it; how to measure it; for a review refer to AU74-119+ 0
PH (GENERAL): Chemist's Term It refers to "potential hydrogen ion concentration"; it denotes the acidity or basidity of liquids of the soil solution; the neutral point is 7, acid solutions are lower than 7, basic solutions are higher; pH range for orchids runs from 5.5 to 7.5, 5.5 to 6.5 the optimum. A68-19; OR66-316 0
PH (GENERAL): Conditions; Growing Under Controlled Levels 4.5 to 5.0 is "very strong acidity" and 5.0 to 5.5 is "strong acidity" and are the leveIs at which orchids grow better; indirectly, pH affects the availability of the fertilizer elements to the plant; formulae for fertilizers suitable for cattleyas, phalaenopsis, and seedlings are given in detail with simplified substitutions offered; growth response reported outstanding; refer to A69-126+ 0
PH (GENERAL): Cymbidium Compost How to test for it: obtain a pH testing outfit from a scientific supply house, which includes a solution, color chart, barium sulfate, distilled water and test tubes; it has a possible accuracy rating of 0.7 to 0.3. A63-478The most desirable range is pH 5.0 to 6.0. A63-478; cymbidiums grow best with a pH of about 6.0 or 6.5; when a mix breaks down and the pH drops to 4.5 or 4.0 in two or three years the roots will die. OA78-100 0
PH (GENERAL): In Nutrition of Seedlings With a suitable medium, the growth and increments of weight of small plantlets are not affected by the initial pH. W9-67 0
PH (GENERAL): Meaning Alkalinity or acidity of a medium; 7 is neutral; values below 7 indicate acidity,- above 7, they indicate alkalinity; for orchid seed germination a pH of 4.8 to 5.5 is required; adjustments can be made by adding a base (alkali) or an acid. OBII-247 0
PH (GENERAL): Of Cymbidium Composts The pH of many components are given their pH ratings over a period of time in composts, the effects of alkaline water resulting in high pH; refer to AU81-102 0
PH (GENERAL): Of Fertilizer A pH8 to 9 of the 30-10-10 fertilizer is natural and should not be adjusted because the alkaline state changes to the acidic side when used by the plant. A81-27 0
PH (GENERAL): Potting Media Acidity, alkalinity and orchids: the definition of pH; the pH scale; pH and orchids; control of pH, etc.jrefer to AU80-37+Test for pH using litmus paper: soak several tablespoons of the media from an established plant in about three times its volume of distilled water for eight hours, filter it and measure the pH with litmus color kit. A80-229 0
PH (GENERAL): Testing by a Cheap Method Buy an aquarium test kit, complete with test tube, color code; it is accurate to one-tenth of a pH point; and an indicator; cost is about a dollar (in 1969); test media or water. A69-403 0

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