It’s possible to create the perfect growing environment to maximise yields. This article looks at the different variables and how they can be controlled in an indoor grow with a focus on hydroponic cultivation.
There are four main factors to consider when trying to create the perfect growing environment:
- Light – Bright but not too bright.
- Temperature – Comfortable for you, comfortable for your plants.
- Nutrients – Nitrogen (N), phosphorus (P) and potassium (K).
- Air – Controlling humidity helps plants grow faster and can increase resin production.
The amount of light you give your cannabis is the main factor that determines your yields.
All plants are different but can be placed into categories based on light needs per day. This is known as Daily Light Integral (DLI). DLI is the amount of PAR received each day as a function of light intensity and duration. This is known as moles per square meter per day (umol/m2/d). A direct correlation between how much PAR your plants are exposed to and for how long each day. Generally, the vegetative stage of plant growth requires 16 – 24 hours of light per day, while the flowering stage requires up to 12 hours of light per day.
The GroLab PowerBot is perfect for automating light schedules.
Below is a general breakdown of how much PPFD is needed for plants to thrive during the different stages of growth.
|Sustainable Veg||Production Veg||Flowering Plant|
|50 – 200 umol/m2/s||150 – 400 umol/m2/s||400 – 1 000 umol/m2/s|
These numbers vary based on type of plant and environmental variables like the introduction of carbon dioxide into the environment. 500 – 1000 umol/m2/s has been noted as an optimum for growth. Less than 500 umol/m2/s and growth will be slow. Plants require additional CO₂ to utilise more than 1 000 umol/m2/s.
You will get the most from your indoor grow lights by reflecting light at your plants. Instead of letting the walls of the grow space absorb extra light from your grow light, you can use a reflective material to bounce it back towards your plants. This allows you to squeeze more yields out of the same grow light without having to change anything else about your environment.
The easiest way to ensure good reflection and to create the perfect growing environment is a good grow tent.
Mars-Hydro build excellent grow tents with no plastic corners and extra thick Mylar with a 99% efficient reflective surface.
The perfect growing environment needs to consider the ambient or air temperature as well as the temperature of the root zone. These temperatures also change depending on the stage of plant growth. The table below summarises the ideal temperatures.
|Ambient||20 – 30 °C||18 – 26 °C|
|Root zone||20 – 26 °C||20 – 26 °C|
Nutrients are a critical factor of cannabis cultivation. The trio of macronutrients nitrogen, phosphorus, and potassium are the fuel for the marijuana growth engine. NPK base nutrients cannot be applied in the same ratio for the complete cannabis lifecycle. Strains also differ and a close eye is necessary to spot problems. However, a rule of thumb on the different NPK ratios and plant stages is provided in the table below.
|Vegetative||Early Flowering||Late Flowering|
Nutrient brands will differ in ratios between Grow, Micro and Bloom products and hydroponic growers are advised to start by applying 25%-strength feeds and work up from this base level.
Some strains, especially indica varieties, tend to respond better to higher doses of fertiliser; the more sativa present usually corresponds to fewer nutes required. Hybrids and autoflowering strains occupy the middle ground, with some leaning toward a preference for lighter or heavier doses.
pH, EC and Micronutrients
Branded nutrients will contain micronutrients and it is best to follow their instructions when dosing.
EC stands for electrical conductivity. For the cannabis cultivator, and especially hydroponics growers, EC measurement is essential to applying nutrients correctly. The perfect EC value is different for each cannabis strain. In general heavy-feeding indicas prefer higher EC values of 2.5+, while some light-feeding sativas prefer a low EC of 1.0 or they will become over fertilised.
The ideal pH for hydroponics is 5.5 – 6.5, with the sweetspot considered to be at 5.8. The GroLab TankBot is able to monitor and correct the pH and EC levels of your nutrient solution.
Making sure your plants always have a gentle breeze and plenty of fresh air will not only get your plants to grow faster, but getting this right also prevents problems. Basically, you want a nice, gentle breeze moving over and under your plants if possible. If all the leaves are being gently rustled it’s perfect. You don’t want to point a fan directly at your plants, but you also don’t want any leaves sitting in stagnant or hot air. A small oscillating fan or two in the grow space can work wonders.
In addition to making sure there’s air moving around in the grow space, it’s also important to vent out heat from your grow lights, especially if it’s getting too hot in your grow space while they’re on. All the air in the tent should be replaced by new air every 1-3 minutes for the best results. It is always better to have a fan that is too large instead of too small.
Unless it’s very high or low, humidity usually won’t cause any major problems with your cannabis grow. However, there are a few tricks with humidity to get faster growth and more resin production on your buds.
|Relative Humidity (RH)||70%||40% – 60%||40% – 50%||40% – 45%|
Plants breathe carbon dioxide (CO2), but when growing using lower powered grow lights (like CFLs or fluorescents), there’s often more than enough CO2 in regular fresh air for your plants to be able to process all the light they’re being given. If your plants don’t need more CO2, it won’t help very much to add more, because they’ve already got more CO2 than they can use.
The situation is different when there’s more light being provided than your cannabis plant can naturally use. In high-light situations, supplying more CO2 can allow your plants to use more of that light, which results in increased photosynthesis. Getting your plants to produce more energy from the same amount of light, will reward you with faster growth and bigger yields! The ideal range of CO2 is 1 000 parts per million to 1 500 parts per million.