In order to be a successful gardener, you need to know what a plant needs to grow.  Plants are nature’s solar collectors.  In order to perform the miracle of photosynthesis, plants need carbon dioxide from the air, water from the soil or air, and sunlight to form carbohydrates and give off oxygen:

    Photosynthesis  is how plants make food for all life on earth (except for extremophiles that live in geochemically active areas such as underwater volcanoes and hot springs).

    The opposite of photosynthesis is respiration.  All plants and animals respire when they unlock the energy stored in the carbohydrates that were created through photosynthesis.

    Other elements are also necessary for plant growth.  When I was in school I learned a mnemonic to help remember nutrients essential for plant growth: C HOPKiNS CaFé Mg’ed By Mne CuZns Mo & Cleo.  Since then a few more elements have been discovered to be essential or beneficial for plant growth: Co, Ni, Si, Na, V, Se.  In the following paragraphs, I list just some of the key roles and benefits of these elements play in plant growth.

    The first three, Carbon, Hydrogen and Oxygen are essential for photosynthesis and respiration as described above in the form of carbon dioxide (CO₂),  oxygen (O₂ ), and water (H₂O).

    The next three are the primary macronutrients; represented by 3 numbers as percents on a fertilizer bag: Nitrogen : Phosphorus : potassium (K).  Nitrogen is absorbed as nitrate (NO₃^–) or ammonium (NH₄⁺).  It is necessary for the formation of amino acids, the building blocks of protein and is directly involved in energy reactions such as photosynthesis and respiration and is essential for cell division and plant growth.  Phosphorus is absorbed as phosphate (H₂PO₄^–).  It is also involved in energy reactions and cell division.  It promotes root growth and improves the quality of fruits, vegetables, and seeds.  Potassium (K⁺) activates enzymes and is essential for protein synthesis.  It also is important for the formation of starch and the translocation of sugars.  It regulates the opening and closing of stomata and improves winter hardiness, drought tolerance and increases disease resistance.  You can purchase test kits that will tell you if you need to add these nutrients to the soil—Nitrogen needs to be replenished most frequently.

    Secondary in importance are calcium (Ca⁺⁺⁾, magnesium (Mg⁺⁺) and Sulfur in the form of Sulfate (SO₄^—).  Calcium is an important structural element in cell walls.  It is important for cell division and formation.  It is also necessary for good fruit set.  Magnesium is a key element used in chlorophyll production and activates many plant enzymes.  Sulfur is an integral part of amino acids and helps develop enzymes and vitamins.  It also promotes nodule formation in legumes.

    Micronutrients are used in very small amounts but are still very important for plant growth.  Iron (Fe⁺⁺⁺) is required for the formation of chlorophyll.  It carries oxygen and is an activator for many biochemical processes. Boron is absorbed as borate (H₂BO₃^–).  It is essential for the formation of cell walls and seeds, pollen germination and growth of pollen tubes.  Manganese (Mn⁺⁺) aids in chlorophyll synthesis and activates many enzymes systems.  Copper (Cu⁺⁺) catalyzes several reactions and performs major functions in photosynthesis and reproduction.  Zinc (Zn⁺⁺) aids plant growth hormones, enzyme systems and seed formation. It is necessary for chlorophyll production, and carbohydrate and starch formation.  Molybdenum is absorbed as molybdate (MoO₄^–).  It is required to form enzymes that convert nitrate to ammonium and inorganic phosphates to organic phosphates.  Chlorine or Chloride (Cl^–) aids photosynthesis and is involved in osmotic transfer regulating the opening and closing of stomata.   With some exceptions, micronutrients are rarely deficient.  Check with your local extension agent to find out which are likely to be deficient in your area—some crops are more sensitive to certain deficiencies and are more likely to exhibit typical symptoms of deficiency.

   The following elements have also been found to be beneficial in some plants.  Cobalt (Co⁺⁺) is required for nitrogen fixation in legumes.  Nickel (Ni++) is needed for enzymes that break down urea to available nitrogen and is required for seed germination and iron uptake.  Silicon is taken up as silicic acid (H₄SiO₄).  It is a component of cell walls, helps resist insects and disease and improves heat, drought and cold tolerance.  Sodium (Na+) can substitute when potassium is deficient.  It is used more often in desert and seaside plants.  Vanadium is essential for green algae and may be beneficial to larger plants in small quantities.  In large quantities, vanadium interferes with the uptake of phosphorus (H₂VO₄^–substitutes for H₂PO₄^– )—It has been referred to as “junk food” for plants.  Selenium is taken up by some plants and may be beneficial for some, but it is toxic to others.

Because of all these nutritional needs I find that it is much easier and less expensive to grow plants in soil, where they may be able to absorb essential micronutrients, naturally. High Tech systems such as Hydroponics are expensive and failure is common because of missing nutrients or system design flaws and/or maintenance issues.

   Plants may absorb other minerals—even gold.  Many cause no problems; others are pollutants that are toxic to plants and/or the consumers of plants.

    Temperature plays a key role in many of the chemical reactions involved in plant growth.  Most plants are able to grow at warm temperatures unless water is a limiting factor.  Many plant species are adapted to grow at colder temperatures.  The USDA plant hardiness map shows different regions in the United States based on average minimum temperatures.  Most garden encyclopedias will give hardiness zones for each listed species.  This is to help you determine if a plant you are interested in will survive in your climate.  In the western states, a better system is used in the Sunset Garden Encyclopedia—it takes other climate variables into account.  Consulting hardiness zones for native plants is usually not necessary—they should already be adapted to your climate!