Above Ground Parameters

Light

Essential Notes

  • Light up, plant metabolism up, water consumption up
  • A DLI (moles of photons per meter squared per day) of 30 will grow a plant, 60 is a sunny summer day
  • The spectrum of your light determines what season the plant believes it is in.  Blue shifted light means spring and foliage growth (veg).  Red shifted light means spring is over and flowering should start (flower).
  • No light pollution. The plant may respond to spectral anomalies with an unintended biological response, i.e. flowering when you don't want it to.

Discussion

Parameters related to light are water, quantity and color. We know plants need light to create light energy into sugars used in metabolism and growth. When we increase light, we increase plant metabolism, which in turn increases water consumption. So, if you increase light, you will increase water usage. At approximately 1500 PPFD/PAR (micro moles of photons per square meter per second) it may be difficult to keep enough water available! Another way we can measure light quantity is with DLI, which stands for daily lighting integral (most commonly used in greenhouse environments). This is just a fancy way of saying we take the total of all photons falling upon the area of one square meter over the course of a day, measured in moles (a dimensionless measurement). It is the total quantity of light your plants received that day measured by a number in photons.  The spectral composition of your light determines what season the plant thinks it is in. If your light is blue shifted, the plant thinks it is spring and puts its energy into foliage growth. Red shifted light means the growth phase has ended and it is time to create flowers. Because the spectral composition of your light has a direct effect on the plants genetic expression (limited to flowering or growing in this case) it is important to ensure there is no light pollution that might cause an undesired effect.

Temperature, Humidity, and Wind

Essential Notes

  • Temperature, humidity, and wind should not be considered apart from one another
  • Temperature: 77-86°F or 26-29°C
  • Humidity: 60% is optimal.  40-70% is acceptable
  • Wind: 1 meter/second or leaves moving slightly

Discussion

Temperature, humidity, and wind should be considered a single parameter as the combination of the three creates the optimal growing environment for a plant.  Temperature is important because it has an effect on the water carrying capacity of air and the fact that specific plants prefer different temperatures. As temperature goes up the more water air can hold before it becomes saturated (rain/snow). This, combined with wind and humidity (amount of water already in the air) allow plants to breathe properly. Just as humans take in oxygen and exhale carbon dioxide, plants take in carbon dioxide and exhale oxygen and water vapor.  Because plants cannot move we need to bring carbon dioxide to them and remove excess water vapor transpired through the leaves. Water vapor out from the leaves equals water in from the roots, which is the source of our nutrients.  Low wind means low transpiration and sub-optimal carbon dioxide availability which means low nutrient uptake and slowed photosynthesis. 

Carbon Dioxide

Essential Notes

  • Beneficial
  • Keep above 400 parts per million (ppm)
  • <400ppm means your plant is suffocating - it uses carbon dioxide to breathe as humans use oxygen

Discussion

Atmospheric carbon dioxide (CO2) is approximately 415 parts per million (ppm).  Keeping your CO2 at or above this level is necessary.  Going below it will result in suffocating your plants and you will experience growth issues.  If you have an enclosed room with many large plants on a long photoperiod (18-24 hours per day), they will most certainly use up the available CO2.