 | Pot Culture: BUSH DOCTOR |
 
The principles of growth, and the importance of leaves
NORML News Winter 2003
Plant physiology is the part of biology which is concerned with the way plants grow and flower. Plants change CO2 and H2O into glucose under the influence of light. Glucose is, in fact, stored light energy, and the leaves are sugar production factories for the plant
Removing leaves reduces the plants capacity to photosynthesise. This means leaves should only ever be removed if they are yellowing and dying or diseased.
Glucose is the chemical building block for the structure and sturdiness of the plant. From glucose, the plant makes cellulose, the material which gives plants their structure. The chemical process in which carbon dioxide and water are converted into glucose is called photosynthesis (from the Greek 'photos' = light, and 'synthesis' = to compose). Chlorophyll, which also gives plants their green colour, is indispensable for this process. If all the conditions are right, the following chemical reaction occurs:
6CO2 + 12H2O = C6H12O6 (glucose) + 6O2 (oxygen) + 6H2O
We can deduce a number of things from this formula. To get one part glucose, we need six parts CO2 and 12 parts H2O. There must always be sufficient carbon dioxide available, otherwise plant growth will reduce.
When we look at this process a little closer, it actually involves two different chemical reactions. The first is called photolysis. In photolysis, water is broken down into oxygen (O), and hydrogen (H). Both light and chlorophyll are necessary for photolysis. This is called the light response. The second chemical reaction is called the dark response. As the term suggests, no light is necessary for the dark response. With dark response, carbon dioxide is converted into glucose, with the help of the hydrogen produced during the light response. The distinction between the light- and dark reaction is of interest to the home grower in order to gain insight into the manner in which the plants must be illuminated (and sometimes kept in darkness). The plants grow optimally only when a good balance is found between the light and dark reactions.
Water is drawn up from the roots through the stem into the leaves where it joins with CO2. Tiny pores on the underside of the leaf aid in this process called photosynthesis. In order for this to occur the leaf's interior tissue must be kept moist. These tiny pores called the stomata open and close to regulate the flow of moisture preventing dehydration. They also regulate the outflow of water vapour and waste oxygen. It can be seen that the water/nutrient system is essential to photosynthesis, as it is in the transportation of the essential elements to the leaf structure that enables photosynthesis to occur.
Nutrients consist of elements that the plants utilise to produce sugars and carbohydrates that in turn are changed into proteins and other complex substances. This process is an essential part of photosynthesis.
There are six major (macro) elements and six minor (micro) elements that are also known as trace elements. Nitrogen, Phosphorous, Potassium, Calcium, Magnesium and Sulphur are the macro elements. The micro or trace elements are Iron, Manganese, Boron, Zinc, Copper, and Molybdenum.
A good nutrient solution will have the right balance of all the Macro and Micro elements.
Carbon Dioxide (CO2)/Oxygen (O2)
Carbon Dioxide, as previously mentioned, is absorbed through the stomata and is essential for healthy growth. In any enclosed growing environment the air needs to be constantly exchanged to make sure adequate CO2 is available, as it is very quickly used up by rapidly growing plants. Air movement (ventilation and circulation) is therefore critical.
Oxygen, as previously mentioned, is released as a bi-product of photosynthesis, however in order for the root system to develop properly and absorb maximum amounts of water and nutrient, oxygen must be present in the solution. Therefore, water oxygenation - via air pumps and water temperature - is critical to achieve vigorous growth.
Temperature/Humidity
In order to have Carbon Dioxide available to the stomata, reasonable air temperatures and humidity levels are required. Excessive temperatures reduce chemical/photosynthetic activity within the plant. Similarly, excessive humidity will reduce the plants capabilities to process CO2. This is because moist air suffocates the stomata, reducing its ability to collect the necessary amounts of carbon dioxide needed for vigorous growth. Temperature affects the root system differently from the stem, leaf and flower structures. Excessive water temperatures will reduce available oxygen to the root zone. The root system can become damaged as a result of this, which in turn affects the plants ability to uptake nutrition. Oxygen starvation, as a result of excessively warm water, is the key reason for root rot in hydroponic systems.
Keep plants at a reasonable height. Generally plants are kept relatively close together and as they get bigger they compete for light. In addition to this, HID lighting has limited depth of penetration so only the top most pars of the plant will get good strong light. A 1ft plant when switched to 12/12 will finish at 2 ½ - 3 foot.
Flower development = light availability (depth of penetration and intensity). A common mistake that beginner growers make is growing plants too high and/or growing too many plants within too small an area. Too many plants competing for light will only receive good light levels on the very tops of the plants and the result of this there will be flower mass on top of the plants with very little flower development lower down. It is more productive to have fewer plants that are receiving more light to get even flowers from the bottom to the top. Similarly, plants that are too tall for the available light will only receive good light high up on the plant and the flowers will only be primo high up on the plant. This is why experienced indoor growers generally grow shorter or more controlled plants (pruning, bending etc), or where large plants are grown they have tons of light from big 1000 watters. Healthy plants grown from start to finish disease free, insect free, fungus free, with healthy root systems, optimum environmental conditions, balanced nutrition and careful use of additives from will greatly improve your final yield.
Don't pick too soon - patience grasshopper, flower weight and potency increases in the last 2 weeks of flowering. The flowers may look big but growth activity may still be taking place and the bud may not be solid and just puffed out with water. Wet herb is at least 2/3rds water, so let them ripen. NICE.
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