GROWERS INFORMATION - ARTICLE - WHAT MAKES YOUR GARDEN GROW

To best care for any plants the first approach is to think like a plant. At a basic level, humans need vitamin supplements to aid in digestion, oxygen utilization, and muscle building because these essential vitamins and trace mineral elements are not found in adequate supply in our rapidly degrading daily diets. Just the same, scientists have identified 16 essential elements (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, O, C, H) that plants require for normal metabolism. Plant material has also been found to contain as many as 60 trace elements, mostly from soil and water impurities, but some of those mysterious elements can make all the difference in proper metabolic function.

Supplying your plants with the perfect amount of readily available nutrients at just the right time is no easy task. Fortunately, this article is designed to demystify enough about plant metabolism to help you make better informed decisions. Understanding plant biochemistry is the first step in assessing your choice of nutrient formulations, organic materials, grow mediums, activators, microbes, water quality and treatment, “boost juices” and “magic mists.”

Metabolism 101

Plant nutrition and metabolism is a concert of many factors. Not even a single violinist is forgotten. Selection of a cultivar, environmental conditions, presence of raw materials, and efficient nutrient uptake are vital to achieving any planting goal. When one begins to think like a plant, it becomes apparent what areas require the most attention. In general, consider these factors in order of importance: water quality, plant requirements, growing environment, nutrient properties, soil/medium properties and feeding directions.

Special consideration should be given to the nutritional requirements of your chosen plant. In general, leafy, slow-growing, and semi-woody stem plants will require less attention to nutrition than would fast-growing, fruit-bearing vegetables or flowers. An organism’s DNA is its blueprint for construction and survival. If a growing plant was compared to a home under construction and its host environment acted as the building supply yard, one could easily visualize what might happen if a drywall screw was used in place of a lag bolt, or carpet in place of concrete because “nature” was out of stock at that moment in time… Price check on aisle four…  Just like a chain, an organism is only as strong as its weakest link and every building block needs to be combined in the right order, the right place and the right time.

A plant’s life cycle is divided into four stages, each with varying needs.

1.  Germination: Young plants require very few nutrients as their seed pods are filled with simple sugars, amino acids, and hormones. During this stage plants are very susceptible to shock and should be cared for gently. Germination works best in warm, humid environments and can be accelerated by adding a root stimulating hormone, like the auxin, naphthalene acetic acid (NAA).

2.  Acclimation: Once plants have sprouted, it’s time to expose sprouts to the growing environment and nutrient solution. Young plants require low dose fertilizing because their root systems have not yet fully developed and are not capable of utilizing all nutrients. Over fertilizing will damage or kill young plants.

3.  Vegetative growth: This stage is marked by exponential growth and large consumption of nutrients and water.  The demand for Nitrogen (N) and Phosphorous (P) increase as they are essential elements primarily required for the formation of amino acids and energy utilization, respectively. Be careful not to over fertilize at this stage because plants under ideal conditions will uptake more nitrogen than necessary, delaying fruit initiation.

4.  Maturation: A dramatic shift in nutrition, hormone regulation, and water consumption will take place. Potassium (K) and Calcium ions (Ca²⁺) play vital roles in maturation as it is a required element in the formation of proteins, sugars, and oils, as wells as proper function of hormones, enzymes, and ion exchange.

To customize the best nutrient solution, a little research on your plant’s needs would be a good start. Many manufacturers make nutrient solutions in single, two, three and even four-part formulations, allowing the motivated grower to fine tune his/her feeding regiment. Experience and a simple understanding of chemistry will reveal that single part fertilizers are not the best choice because of the large changes in most plants’ metabolic requirements. In addition, many one part solutions have more additives than could possibly remain dissolved in solution. Refrain from buying liquid nutrients that have precipitated crystals at the bottom because those components are unavailable for uptake once out of solution.

Take the time to read labels!  If there is no ingredients label then there are no plant foods in the bottle. State by state labeling regulations require that a Guaranteed Minimum Analysis disclose in detail all of the major constituent salts in solution. Some products make outrageous claims that are physiological nonsense. When the biochemistry of photosynthesis, respiration, and electron transport are better understood it becomes easier to cater to your plant’s needs and separate the reality from the TV show going on at the local grow store.

Photosynthesis

Simply put, photosynthesis uses light energy to reduce (add electrons to) carbon dioxide (CO₂) and water to form sugars as oxygen is released. Electrons and protons are raw energy. Chloroplasts contain chlorophyll and other photosynthetic pigments that harness the sun’s light energy to establish a proton gradient among the chloroplast’s inner membranes. In a complicated series of reduction/oxidation reactions, the Calvin cycle yields one glucose molecule per six ‘turns’, requiring 18 molecules of ATP. 

Respiration

Coupled to photosynthesis, aerobic respiration is the process where glucose from the Calvin cycle is digested to produce ATP (adenosine triphosphate) the molecule responsible for 95% of metabolic energy. Glucose is phosphorylated (addition of energy rich phosphate groups) and split into two three-carbon sugars. These sugars are oxidized (loss of electrons) to pyruvic acid, in turn donating electrons to NAD⁺, reducing it to NADH. This sugar molecule and energy carrier are subsequently used in the Krebs cycle to transfer electrons in the formation of more ATP than was consumed in the Calvin cycle. Oxygen is the final electron acceptor in the electron transport chain with a voltage of 0.82, more than half that of an AA battery. Who knows, maybe our fields of green can be harnessed to put the power companies out of business… sorry, pinch me, I dozed off!        

Enzymes and Cofactors:

All biochemical reactions are catalyzed or accelerated by reaction specific enzymes, often requiring cofactors like Mg²⁺, Mn²⁺, and Fe³⁺. Enzymes are globular proteins that speed reactions by decreasing the activation energy required to carry out the given reaction. Enzymes can accelerate a reaction by as much as a million times, literally, without being consumed. Most cells have the necessary enzymes already present, but vigorous growth or plant stress can deplete the availability of essential nutrients, cofactors, and coenzymes. Coenzymes are vitamins like niacin (B₃) and riboflavin (B₂), essential components of nicotinamide adenine dinucleotide, the afore mentioned NAD⁺ molecule that participates in redox reactions. Coenzymes are also referred to as organic cofactors.

Imagine a plant’s biochemical pathways as a road trip throughout New York. There are very few paths to take to reach the destination, and most likely, a few bridges and tunnels are on the route. These bridges are enzymes that take your car from one landmass to another; effectively accelerating the normal pace it would take you to swim. Of course, there is always traffic at the tollbooth as we trade our ‘cofactors’ for access to the enzyme. The bridge has a max flow rate when it is fully saturated with cars (substrate). Provided that everyone has their money in hand at the tollbooth, traffic will proceed at the fastest rate with the most cars traveling on the bridge.

It is possible to maximize a metabolic function to the extent that a rate-limiting enzyme will allow. Enzymes are coded for by a cell’s genetic material and it is difficult to increase their intracellular concentration. They can be inhibited, competed for, and otherwise regulated. Optimal metabolic efficiency is the ultimate goal.

Apparently, there are many required organic and inorganic nutrients to make these metabolic processes function properly. Most three part nutrient solutions have all these bases covered, but what about supercharging your nutrient mixture? Adding a little bit of this and a little bit of that may boost plant growth and yield or it could completely kill your plants if used incorrectly. Whatever you use, follow the manufacturers label exactly. The biggest factor to consider is cost as anyone will notice these miracle formulas are expensive and sometimes unnecessary.

Optimizing Growth:

Light

For starters, let’s consider optimizing the growing environment. The Calvin cycle contain 12 enzymes, five of which are light activated and rate limiting to photosynthesis. Chlorophyll is the primary photon receptive molecule and is most active in the blue region at 430 nm and the orange region at 663nm. A magnesium atom rests in its center, bonded to four nitrogen based light sensitive ‘antennae’, specialized for the transfer of electrons when illuminated. To maximize light intensity, bulbs should only be used within the manufacturer’s estimated life span. New high output enhanced spectrum bulbs are available with emission wavelengths near optimal combined with lower operating temperature. Cooler lights are more efficient at converting electricity to light energy as no energy is wasted as heat. Temperature and humidity are also huge variables in the rate of photosynthesis. A pH test kit and other sensors would be a good investment and you could always ask a friend to borrow a light intensity meter.

Carbon Dioxide

The relative concentration of CO₂ in the atmosphere is 365 ppm. Studies have shown that air movement can have a large impact on carbon fixation and overall growth. A concentration of 1000 ppm can raise photosynthetic rates by as much as 60%. However, increasing the concentration to 1500 ppm will cause stomata to close and photosynthesis will stop. This is more effective in some plants than others and should be applied during the light cycle.

Oxgyen

In much the same manner, root zones and reservoirs need to have a favorable concentration of diffused oxygen. Root rot occurs when O₂ levels are very low and anaerobic respiration occurs releasing lactic acid and ethanol, also known as fermentation. This is prevented by choosing a quality medium with good water and air retaining properties. The ideal medium for most hydroponic applications is one that:

1) Maintains an equal ratio of air to water.

2) Helps to buffer pH changes over time as well as stabilize levels of nutrients.

3)   Is easily flushed and can be re-wetted after complete dehydration.

4)   Can be reused or is biodegradable.

5) Is inexpensive and easy to use both indoors and out.

As for the reservoirs, cooling, circulating, or bubbling will help keep the nutrient solution clean and oxygen rich. UV and ozone treatment are generally only used for commercial applications and should be performed before adding nutrients or other additives to avoid triggering chemical reactions between nutrient ions in a charged reservoir. Change reservoir water every other week. Keep reservoirs clean, cool and free from stray light as algae will easily contaminate a translucent tank and consume all available oxygen in doing so.

Certain additives like hydrogen peroxide, H₂O₂, will keep the reservoir relatively aseptic. Hydrogen peroxide should only be used in 3% solutions when adding to a reservoir for it is deadly to roots in higher concentrations. For every 10 gallons of nutrient solution, pre-dilute three tablespoons of 35% H₂O₂ to a gallon of distilled water. Mix half of the reservoir with H₂O₂ and the other half with nutrient solution. Combine the two while mixing gently, taking into consideration the total volume of the reservoir. It is unlikely that dissolved oxygen content will significantly increase in low concentrations or without the presence of peroxidases to break it down. Be sure to practice this before killing your prizewinners. 

Water Quality:

Water quality is as important as any nutrient formula. Many water supplies have levels of contaminants that could be harmful to your plants. Solution pH (ideally 5.5 to 7) is also vital as some nutrients become insoluble or unavailable. Most commonly encountered contaminants are sodium chloride (table salt), boron, and calcium bicarbonate. Besides being toxic to plants in high concentrations, calcium bicarbonate will clog hydroponics systems. Reverse osmosis is an expensive but effective way of purifying even the most contaminated water and should be employed by every serious grower.  Nutrient formulas designed for “hard” water use are questionable.  In some parts of New York, water is 32 ppm, while upstate it’s 1100 ppm. In Arizona I hear it is 200 ppm.  There is no way to compensate for such a wide range of water hardness other than to start with pure water.  Invest in an RO system and stick to the time tested and true soft water formulas.

Dissolved salts reduce the osmotic potential of water and increase the energy needed for nutrient uptake while disrupting the intracellular osmotic balance. Lettuce, strawberries, and peppers are among the most salt sensitive crops. Elevated sodium levels above 110 mg/L will result in wilted leaves, stunted growth and fruit set, and can cause deficiencies in calcium, magnesium, and potassium. Boron is a common water contaminant and exists in a fine balance in plants. Trace amounts of boron are essential in many biochemical processes but concentrations above 0.75 mg/L are harmful. Chloride is a common fertilizer contaminant and should be monitored closely, not to exceed 180 mg/L. In general, leaves will show signs of toxicity and deficiency first. Close attention should be paid to whether symptoms appear in new or old growth as the location of trace elements serve as an indicator to the culprit.

Common Misconceptions:

Many organic fertilizers extracted from seaweed or fish emulsion can contain harmful levels of sodium, ammonia, and heavy metals. “Boost” juices are often high in sodium especially if they contain organic counterparts or are super concentrated. In addition, organic fertilizers are not suitable for media-less, pure-water hydroponic applications for many reasons. Organic debris easily clogs emitters and filters. They also contain unprocessed amino acids and sugars that serve as a breeding ground for bacteria that will consume the very dissolved oxygen your roots are starving for and releasing potentially harmful byproducts into solution. Not to mention, where are all the aerobic bacteria that are required to break down this stuff going to live? Scuba anyone? Michael Christiansen said it best – Organics is feeding the soil, hydroponics is feeding the plant. If you want to grow in water, keep the dirt in the garden outside where it belongs.

Symbiotic (mutually beneficial) bacteria and fungi can be introduced in the growing environment. Specialized bacteria can be used as pest or fungus control. Beneficial mycorrhizal fungi are best applied in root zones where they actually penetrate root membranes, increasing the effective surface area by 10 to 100X. They also serve as bioactivators, capable of breaking down complex nutrients, making them more available for uptake. These are very specific processes and need special consideration of plant species and grow method compatibility.

Some solutions will have bioactivators in them. The term activator refers to a molecule or organism that alters the chemical state of minerals, vitamins, or other substrates, making them more easily utilized in the plant. Humic acid is the remnants of amino acids, carbohydrates, and decayed plant matter that is thousands of years old. Humates are the salts of humic acids, which form complexes with phosphorus and trace elements making troublesome ions more readily available. Fulvic acid is the acid radical found in humic matter and is readily soluble. Iron, calcium, phosphorous, and magnesium are the most insoluble elements in a nutrient formula and are facilitated by fulvic acid.

The acid-growth hypothesis of auxins may also apply to humic and fulvic acid. The auxin IAA stimulates H⁺ pumps in cell walls. This acidification in turn stimulates pH dependent enzymes such as expansins that facilitate cell division by breaking load-bearing bonds in cell walls. Loose cell walls facilitate the translocation of materials necessary for cell division.

Magic plant tonics are usually hormone, enzyme, cofactor, and micronutrient formulas that aim to facilitate normal plant metabolism and nutrient uptake. Hormones are organic compounds produced in one part of the plant and transported to another to stimulate or inhibit growth. Plant hormone theory is very complex because it depends on the presence and concentration of other hormones, non-hormonal factors like Ca and Zn ions, environmental queues, and tissue specificity. Plant tonics claiming to affect multiple stages of growth as an ‘overall invigorator’ are nonsense because it is impossible to formulate an effective hormone supplement, in one bottle, to cover the wide range of precise stimulators over time. For example, auxins alone promote root and cell growth. In conjunction with cytokinin and gibberellin, the trio prolongs plant death. Upon flowering, shorter light cycles reduce auxin synthesis, triggering leaf senescence and abscission.

These tonics are effective mostly as foliar sprays because it has been proven that leaves are adapted to nutrient uptake. Although this method is not as effective as traditional fertigation, when used supplementarily, they combine to provide a very effective system at delivering hormones, micronutrients, trace elements, and other cofactors through a wider range of the plant’s growth stages. Foliar sprays should be used with a wetting agent to reduce surface tension in an effort to increase coverage and availability.

Conclusion

As you may have gathered, there’s a lot more going on inside your plants than one might imagine at first glance. Understanding how to best care for your favorite cultivar has to start with an understanding of how plants work from the inside out. 

Making the right decisions about when and what to feed and what to forgo completely are much easier once you know the fundamentals. Last but not least, plants are just like computers, Garbage in, Garbage out so feed your garden well because we are of course, what we eat.

References

Christie, Bruce, and Mike Nichols. “Salinity & Hydroponics”. Maximum Yield. April, 2004. Pp. 44, 46, 50, 54, 56.

Moore, Clark, Vodopich. Botany, 2nd Edition. New York: McGraw-Hill, 1998.

Morgan, Lynette. “Not By Water Alone”. The Growing Edge. Volume 15, No. 6, 2004. Pp. 35-52.

Taiz, Lincoln, and Eduardo Zeiger. Plant Physiology, 2nd Ed. Sunderland, Sinauer Assoc., 1998.

Roberto, Keith. How-To hydroponics, 4^th Ed. The Futuregarden Press. New York: 2003.