Promoting Photosynthesis

Photosynthesis: How it Works

The energy of light (usually from the sun) is harnessed to fix nutrient minerals from the environment.

• Plants use phosphorous to help harness this energy.

The energy from light helps the plants to oxidize water (H2O) in to free hydrogen
The same energy is then used to fix carbon directly from atmospheric carbon dioxide (CO2), and with the hydrogen, synthesize carbohydrates (Calvin-Benson cycle).

• Carbohydrates are then used for energy and to form other carbon based molecules (e.g. cellulose, proteins, THC)

Simply put:
Light + CO2 + H2O = C6H12O6 (glucose, a simple carbohydrate)

• An important bi-product is atmospheric oxygen (O2)

To promote optimal growth, indoor cannabis requires special attention to the artificial lighting provided.

Water (H2O), a key ingredient for Photosynthesis

• Water is critical to all plant processes, especially transpiration and photosynthesis. During photosynthesis, water (H2O) is oxidized into free hydrogen. This hydrogen is fixed along with carbon (from atmospheric CO2) to form carbohydrates and other forms of cellular energy (e.g. ATP). Additionally, water keeps many nutrients in their available form and transports them to where they are needed for plant growth.
• Water is absorbed by the roots and should be readily available at all times. This ensures that nutrients never become unavailable and transpiration is always supplying photosynthesis.
• Watering demands can vary greatly, and are determined by the environment, grow medium, pot size/material, the plant’s root system and canopy size.
• A good watering schedule can ago a long way in preventing setbacks and maximizing yields. This starts with choosing the right soil.
• When creating a watering schedule for your room, start by observing your plant. Allow for your very topsoil to lose moisture before watering again. (It will turn from dark brown, to a lighter brown.)
• Do not allow the soil to become dry

Maintaining this level of moisture:

• Exposes root hairs to additional oxygen
• Prevents stem-rot in young plants
• Combats common pests (fungus gnats)
• Promotes a healthy rate of transpiration
• Ensures nutrients are available

Water Quality

Not all tap water is equal. Many municipal water supplies have high amounts of chlorine and other solids that may be detrimental to plant health.

If your tap-water is known to be “hard” or harshly treated, it may be necessary to invest in a filtration system. If you are unsure, check with your local government to see if a water quality report is available.

• Practical filtration options include Reverse Osmosis, and Carbon Filters
• Many growers test and track the total dissolved solids (TDS) in the water, both before and after any supplemental nutrients are added. TDS is measured by an electronic meter in parts per million (ppm), and gives an idea of the quality of the tap water, and strength of added nutrients.
• Average tap water usually measures between 200 – 300 ppm of TDS.
• Reverse osmosis filtered and distilled water should measure between 0 – 20 ppm of TDS.
• Carbon filtered water should measured between 50 – 75 ppm TDS

TDS and EC to measure nutrient strength

TDS can also be a measurement of nutrient strength in the water.
For soil, 700 – 1000 ppm is normal for water with added nutrients.

• remember, start low and go slow!

Above 1600 ppm starts nearing toxic levels

Feeding and Runoff water can be measured to prevent salinity build up and potential to harm a plant.

The electrical conductivity or EC is another way to measure the amount of solids in a solution and uses the same data as TDS, but on a different scale.

• To get an EC value, multiply the ppm reading by 2 and divide by 1000. Thus, if your EC is 1: 1*1000/2= 500 ppm.

Measurements limits depends on the cultivar, environment, and watering schedule. In general:

• For soil, try to keep TDS below 1200 PPM
• EC should be below 3

Carbon Dioxide (CO2) for Photosynthesis

• Nearly all life on earth is carbon based. Nearly all organic molecules on earth are bound and stabilized by a carbon skeleton. All organic carbon (including the carbon you are made of) was at one point fixed from atmospheric CO2 via photosynthesis. Plants are autotrophic in the sense that they pull their carbon (and other elements) directly from the environment. Animals are heterotrophic because they derive carbon (and other elements) from other life forms (like plants).
• During photosynthesis plants intake CO2 and expel O2.
• It’s easy to see why an indoor grow-space must maintain CO2 in the atmosphere.
• When in an enclosed grow space, plants can quickly deplete the amount of CO2 and enrich the amount of oxygen (O2). Because CO2 is required for photosynthesis and the formation of carbohydrates, depleted levels can greatly limit growth.
• It is important for a indoor garden to account for depleted CO2 levels by either completely exchanging the atmosphere with fresh-air, or by supplementing the grow space with generated or compressed CO2 gas. It is recommended that new growers utilize the fresh air exchange strategy for their first few grows (covered in the previous section).
• Generally speaking, using a fresh-air intake fan to control humidity and heat are enough to also freshen CO2 back up to ambient levels.

 

Understanding Photosynthetic Light

Light is a form of electromagnetic radiation, which travels in waves, and is made of photons.

• These waves lengths carry different levels of energy. (Higher frequency = higher energy)

Animals (including humans) use only a small portion of these waves (visible light) to see.

• Animals see different visible light waves as different colors

Plants and some bacteria also use a similarly small portion of electromagnetic radiation, known as photo-synthetically active radiation (or PAR).

• Most, but not all of PAR is in the visible light spectrum.
• Plants use different PAR wavelength at different photosynthetic efficiencies.

Measuring Light

• Good horticulture lighting companies make lights that provide a lot of energy at a spectrum that more closely matches this PAR graph. Thus, electricity is spent meeting the demanding requirements of photosynthesis without wasting watts on light the plant can’t use as efficiently.
• Artificial lights created to appear “bright” to the human eye are usually measured in Lumens.
• Artificial lights created to promote photosynthesis are usually measured in PAR.
• Remember: Through photosynthesis, plants use PAR, H2O, CO2, and inorganic nutrients to create carbohydrates.