Specific Fertilizer Details


Macronutrients

N-P-K
Most commercial fertilizers in the United States contain macronutrients that are necessary for plant growth.  The three main macronutrients are nitrogen (N), phosphorus (P), and potassium (K).  These micronutrients are listed as concentrations in fertilizers relative to one another such as 10-20-10.  The concentrations are listed on all bags of fertilizers sold with the first number relating to the concentration of nitrogen, the second for phosphorus, and the third for potassium.  Any ratio of these concentrations of elements is sufficient to provide the needed amounts for plant metabolism, however, be careful in using high nitrogen fertilizers so as not to damage the tissue of the plants.

These three macronutrients are necessary for plant growth, development, and cell metabolism.  Nitrogen is important because it is used in producing proteins, enzymes, nucleic acids, and found in chlorophyll.  Without nitrogen present plants have stunted growth and will often die if nitrogen is unavailable.  Phosphorus is found in nucleic acids, phospholipids, and in production of ATP (cellular metabolism and energy).  A lack of phosphorus also causes stunted growth and often leaves that are deep green.  There is no supporting evidence that phosphorus promotes blooms in most plants (see plant physiology perspective), so you may not want to push high phosphorus fertilizers on your plants or spend extra money on them.  You will note that the fertilizer I use has a higher concentration of phosphorus than either nitrogen or potassium.  This concentration is so that I can avoid high levels of nitrogen, and that I do not burn the roots or growth of the plants.  Potassium is responsible for osmosis and ionic balance in cells, opening and closing of stomata on leaves (allowing gas exchange), and as an enzyme activator.  In short, your Stanhopea would not grow and bloom well if they lacked any of these macronutrients.

Other Macronutrients
Other macronutrients that are essential for plant metabolism include carbon, calcium, hydrogen, oxygen, sulfur, and magnesium.  Carbon, hydrogen, and oygen are obtained from the air and water and are essential elements during photosynthesis.  Calcium is used in the formation of cell walls and in the mitotic spindle during cell division.  In my poor quality water, there is an abundance of calcium and salts in the water, so I usually do not have to worry about a lack of calcium.  Only those individuals who use deionized water or filtered water would have to worry about calcium levels.  Calcium is also present in small amounts in many organic fertilizers.  Magnesium is essential in photosynthesis, respiration, DNA and RNA synthesis, and assists in forming bonds with nitrogen.  Magnesium is also involved with enzyme activity.  Sulfur is an essential component in synthesis of coenzymes and vitamins essential to plant metabolism.


Micronutrients

Several Stanhopea species are semi-terrestrial or lithophytes and I therefore treat them similar to other terrestrial orchids such as Sobralia, and Zygopetalum by providing them fertilizer with micronutrients.  These are elements that are essential for plant metabolism and growth.  The fertilizer that I use has trace concentrations of boron, copper, iron, manganese, molybdenum, and zinc.  These are all metal/mineral elements that are necessary for plant metabolism.  Boron may have a role in cell elongation, nucleic acid synthesis, hormone response, and membrane function.  Copper and iron are required by enzymes in redox reactions and in photosynthesis.  Manganese is an activator of eznymes in plant cells for both respiration (citric acid cycle) and photosynthesis.  Molybdenum is associated with nitrate assimilation and nitrogen fixation.  Zinc has a role to play in enzyme activity and chlorophyll biosynthesis.  Plants that lack available iron and manganese can have yellow leaves and appear stressed.

References

Berg, L. 2008.  Introductory Botany: Plants People and the Environment, Second Edition.  Thompson Higher Education, Belmont, California.

Taiz, L. and E. Zeiger 2010.  Plant Physiology, Fifth Edition.  Sinauer Associates, Inc., Publishers, Sunderland, Massachusetts.

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