Fertilizer Basics Ray Barkalow
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6 eople spend a lot of time worrying about what fertilizer to use on their orchids , and manufacturers make so many different blends that it ’ s difficult to know which is “ the right one .” Generally , just about any fertilizer may be used on your orchids , within certain guidelines . To make it really simple , select a formula that does not contain excess nitrogen , but does contain a wide array of minor and trace elements . There are some that feel that those minor ingredients are the most important components of the formula . Of interesting note is the fact that the majority of nutrients are absorbed via only the green tips of the roots and the undersides of leaves . Why do we want to avoid high-nitrogen fertilizers even though they ’ re often specifically called “ orchid food ”? To answer that , let ’ s look at some history . When orchid collecting began , it was noted that the majority grew on the bark of trees . Naturally , that led to the idea of growing orchids using bark as a potting medium , and that was the standard for many , many years . Unfortunately , wet , crumbled bark in a pot will slowly decompose , courtesy of various microorganisms . The little critters also consume a large amount of nitrogen as they work , and would end up leaving the plants nitrogen-deficient , so it seemed necessary to compensate for that in the formula . Unfortunately , more recent research has shown that feeding your plants too much nitrogen can lead to the delaying or outright stopping of blooming , which defeats the goal of the orchid grower . That leads us to the question about the use of “ bloombooster ” formulas . Those are the blends with augmented levels of phosphorus in the formulation . They are commonly used for a number of weeks prior to the start of inflorescence growth , as a way to “ build up ” the plant for blooming . Are they necessary ? My own experience doesn ’ t give me an answer , and when asking that of others , you ’ ll get the full spectrum of responses , but it sure can ’ t hurt .
More recent studies at Michigan State University suggest that blooming is less an issue of boosting phosphorus than that of not overdosing nitrogen , so maybe the effectiveness of the bloom booster formulas is related to the ratios of the two , and not so much the phosphorus level itself .
Nutrient Availability One can surmise the nutrients needed by a plant by determining the mineral content of the plants themselves . Typically , healthy plants are incinerated under controlled conditions and the mineral content in the ash is determined . That information is the basis for the formulations in modern , complete fertilizers . Choosing a fertilizer that contains the correct nutrients in the proper concentrations , however , is only part of the story . A critical aspect that is often overlooked is the availability of those nutrients to the plant . Minerals , whether naturally occurring in the soil or in fertilizers , are only absorbable by plants if they are in the form of ions . The size and reactivity of those ions determines how readily they can be taken out of solution and absorbed by the plants , and the pH of the solution is probably the most significant factor in controlling the ionization of the minerals . Greatly simplified , depending upon the pH , a mineral can be insoluble and unavailable to the plant , soluble , but in a form that is difficult for the plant to readily absorb , soluble and in a form that the plant can absorb with ease , or so soluble and concentrated that it can be toxic . Without going into solubility details of the specific ions , research has shown that a pH of around 5.5-6.5 is ideal for the vast majority of orchids .
Remember that the chemistry of your nutrient solution is determined by both the fertilizer and your water supply . Figuring that most people will use tap water , most general-purpose formulas are designed with a generic array of dissolved solids in mind , and will provide a good pH when used out of the box . If those are used in pure water , reverse osmosis , distilled , deionized , or collected rainwater , it is likely that the pH will
Third Quarter , Vol . 22 ( 1 & 2 ) 2012 - Phalaenopsis