Cannabis is an annual plant, it reaches the end of its lifecycle in the fall, sheds seeds, then dies. During its life, it goes through two distinct phases of growth: vegetative and flowering. The first phase is vegetative when the plant grows branches and leaves. The second stage is flowering when the plant grows buds.
Flowering and vegetative growth phases are regulated by a hormone called florigen. Florigen accumulates in cannabis plants only when they aren’t exposed to long periods of light everyday. When daily light exposure is low, florigen accumulates . After surpassing a threshold florigan causes plants to flower.
The amount of light a cannabis plant receives each day determines its phase of growth. More than 12 hours of light exposure each day and it will remain in a state of vegetative growth. Less than 12 hours light exposure each day and it switches to its flowering growth phase.
Outdoors, growth phases are determined by the number of hours the sun is up each day. Vegetative growth happens in the spring when the days are longer. As the days grow shorter in the fall, daily light exposure drops, florin accumulates, and cannabis plants shift to their flowering phase.
Vegetative growth is typically maintained indoors by attaching lights to a timer device and exposing plants to 16 – 24 hours of artificial light per day.
Growers can control when their plants flower indoors. By maintaining daily light exposure above 12 hours plants will stay in vegetative growth, theoretically forever. Or they can be forced to switch to flowering growth, even only after a short period of vegetative growth, by setting their daily light exposure to 12 hours a day or less.
Indoors, setting the light schedule to 12 hours of darkness per day causes cannabis plants to enter their flowering growth phase. To sustain flowering, plants must be keep in total, uninterrupted darkness. Light leaks can cause a reversal back to vegetative growth.
Darkness is typically achieved inside a tent that can be zipped up, shielding plants from light.
LED lighting is a newer technology for horticultural lighting that generates light by passing electricity through semiconductor materials. It replaces traditional HID lighting that works by superheating bulbs filled with gas.
An LED light is made from light emitting diodes powered by a DC power supply. Some LED lights also have a heatsink, a fan, and sometimes a protective casing.
LED lights are available in different shapes, rectangles, squares, long strip lights, or mounted in tubes.
A worthwhile feature available on some LED lights is a dimmer switch. Plants in early stages of growth need less light than plants in late flowering. A dimmer switch allows the light intensity of a panel to be turned down so it can use less power during the plants early growth stages and then turned up for later stages when plants require more light. This feature can save on electricity costs and reduce heat. It also allows for gradual light increases. Plants prefer gradual increases to intensity, not abrupt change to a higher light level.
Most LED lights are directional, meaning they emit light at 180 degrees, directly down at the plants. Directional light is efficient, saving costs compared to other types of lighting. For example, HID lights emit light over 360 degrees, requiring reflectors to bounce light back at plants. Light that needs to be reflected back is less efficient because whenever light gets reflected some energy is absorbed by the reflector. A straight path to the plant canopy is better.
The chart below shows the light distribution for a 20 x 26” light panel. The numbers indicate light readings taken under the light. It demonstrates how light becomes less intense the further away from the centre point directly under the light fixture.
Reflectors positioned at the sides of the canopy, such as the silver reflective walls of a 4’ square grow tent, will reflect some light, boosting light levels at the sides.
Light panels positioned beside each other can be arranged so that the beams overlap, creating a spread of even intensity over a large coverage area. This is called a grid pattern.
LEDs create light by electroluminescence, which is the phenomenon of a semi conductor material emitting light when an electric field is passed through it. The type of semi conductor material used in LEDs determines the colours of light it emits. For example, indium gallium nitride is a material used for blue and green LEDs, and aluminum gallium arsenide is used for red LEDs. Different semiconductor materials can produce specific wavelengths of light. LED panels that house a mix of different LEDs can output customized light recipes by combining wavelengths.
LED panels are very efficient because they are designed to produce only the wavelengths of light that plants use. In comparison, HID light systems emit a byproduct of infrared light which is not useful for plants and also adds a lot of heat to a grow room.
LED systems also generate heat, but not from a bulb with superheated gasses, as is the case with HID lights. The heat created by LEDs is created by its semiconductor processes.
LED systems generate less heat overall than HID systems. HID systems turn 20% – 40% of power into usable light. LED systems convert about 40% – 60% of power into usable light.
Heat generated by LED semiconductors is removed using passive and active cooling methods. For passive cooling, heat is conducted away from the semiconductors, either through the board the LEDs are mounted on, or a finned heatsink. For active cooling, fans blow heat off the board and heatsink.
Because heat is dissipated away using active and passive cooling methods the front of an LED panel is cool to the touch. Plants can be positioned very close to a light without a risk of starting a fire. Having plants positioned close to the light also saves energy. The further light has to travel from the panel to reach the plants the less intense it gets. The further away the plants are from the light source, the more power a fixture has to draw to generate enough strong light for the plants. Lights don’t have to work as hard when plants are closer to them.
A good LED light panel should last a very long time if properly cared for. Although it varies from light to light, an LED grow light lasts on average 60,000 hours. In comparison, HID light systems last only 20,000 hours.
The output of an LED light will degrade over its lifespan. Over 60,000 hours, a loss of 3-5% can be expected.
LED light boards and heatsinks are solid state. There are no moving parts that can become detached or gasses to leak so they aren’t prone to breaking down over time.
Excessive ambient heat will shorten the lifespan of LED lights and degrade their performance. To prevent heat damage, the ambient temperature in the grow room should stay under 30°C.
To prevent damage from static electricity, anti static gloves should be worn when handling LED boards. Devices and equipment in the production area should be well grounded.
Some LED boards are housed in a protective casing. The casing is sometimes rated for water and dust resistance with the Ingress-Protection code, or IP. It is expressed as IP with two numbers afterwards. For example, IP64. The first digit indicates dust resistance and the 2nd digit indicates water resistance. The symbol X in place of either the 1st or 2nd number indicates that there is no data available.
Dust resistance rating (1st digit):
less than 5 = poor dust resistance
5 = some dust resistance.
6 = completely protected from dust.
Water resistance rating (2nd digit):
less than 3 = resistant to some drips, but vulnerable to sprays.
3 = resistant to damage from spraying water.
6 = resistant to powerful jets of water projected at enclosure.
LED lights can be run without a protective casing as long as they aren’t sprayed directly with water and are cleaned periodically using isopropyl alcohol to remove dust.
There are several measurement types that get used to describe energy output. Most common are LUMENS, LUX, PPF, PPFD. They don’t all measure light output the same way.
LUMENS and LUX measure visible light only. Because plants use some light that is invisible to humans, LUMENS and LUX don’t always account for all the light available to plants.
PPF and PPFD measure all the light plants use, including visible light and invisible light, making them the most accurate measurements for horticultural lighting.
LUMENS and PPF are measurements taken at the fixture. They measure raw output. They are good measurements to use when comparing power draw vs. output to determine how efficient a fixture is.
LUX and PPFD are measurements taken at a distance from the fixture, accounting for light falloff and reflection. They are highly accurate and useful measurements because they indicate exactly how much light a plant’s leaves are receiving.
PPFD measurements are captured by lighting manufacturers using special equipment in a lab environment. Light manufacturers include PPFD as part of their published specifications for their lights, usually.
The best way to present PPFD measurements is in a chart that illustrates the intensity and coverage of the light at a stated distance from the canopy. To create these charts, a tester hangs a light above a graph that represents a coverage area. With the light turned on, a quantum sensor takes spot PPFD readings at the intersections of the graph. The data is compiled into a PPFD chart that makes it easy to visualize the light’s performance.
A good PPFD chart includes these features:
• Readings expressed in micro moles per square metre per second (μmol/m2/s)
• Distance the readings were taken from the light. For example, 12″ from light, 24″ from light.
• Multiple readings taken in a grid pattern over a wide coverage area, not just a single reading.
• Indicates if the readings were taken with or without reflection at the sides to reflect back light and boost the light levels. It’s better if the readings are taken without reflection because reflection could be used as a way of exaggerating the capabilities of a light.
Some manufacturers publish only a single PPFD measurement, not a chart that includes multiple readings. This can be misleading if the measurement was taken directly under the fixture where light is strongest. If a single PPFD reading is given, it should be an average of several readings. For example, an average PPFD over a 4′ x 4′ coverage area.
The amount of PPFD required for cannabis depends on its stage of growth and the strain. The recommended light levels listed below will work for most strains. Keep in mind that hybrid strains with more southern genetics (sativa) require more light than northern varieties (indica). The measurements can be modified up or down 10-20% depending on the strain.
Also consider the depth of the canopy. As the charts above demonstrate, light becomes less intense the further it has to travel. All buds should receive adequate illumination, not just the ones at the top. If the canopy is a foot deep, consider if the amount of light reaching the lower half is adequate.
Below are the recommended PPFD levels for each stage of growth:
Seedlings, clones: 100 PPFD
Vegetative, moderate growth: 310 PPFD
Vegetative, heavy growth: 620 PPFD
Flowering, moderate growth: 620 PPFD
Flowering, heavy growth: 925 PPFD
PPFD is sometimes alternatively expressed as μmol/m2/s.
LUX is another useful measurement because although it only measures visible light, it can be measured using a commercially available handheld device. This gives LUX a distinct convenience advantage over PPFD which can only be measured in a lab. A LUX metre is a fantastic tool for taking spot measurements that every grower should own.
Below are the recommended Lux readings for each growth stage:
The efficiency of a lighting system is calculated by dividing input power (WATTS) vs. output (LUMENS or PPF).
Watts is an international measurement representing 1 unit of input power. It is the most important measurement for determining how expensive a light is to run because it’s the one used by electrical utilities for calculating the cost of electricity.
Electrical utilities calculate costs based on kilowatt hours (kWh). A kilowatt hour is how much energy gets used by a 1000w appliance in 1 hour. For example, a 2000 watt appliance would use up 1 kWh in 1/2 an hour. A 500 watt appliance would take 2 hours to use up 1 kWh.
The best light is the one that outputs the most power for the least amount of money.
Divide WATTS with an output measurement, either LUMENS or PPF. This results in a number you can use to compare the efficiency of different light systems. The lower the number, the cheaper a light costs to run.
Sometimes efficiency measurements are already calculated by light manufacturers and published with their product specifications. Efficiency measurements are expressed as PPF/W (PPF per watt), or lm/W (LUMENS per watt). PPF/W is sometimes alternatively expressed as µmoles/joule.
The wavelengths of electromagnetic radiation span from the very short wavelengths of cosmic and gamma rays, to the very long waves that are used for radio broadcasting. The wavelengths plants use for photosynthesis fall within a very small portion of the total electromagnetic spectrum called the visible and near visible light spectrum.
The wavelengths of the visible and near visible light spectrum is measured in nanometers, 100 nm – 1000 nm, which refers to the length of the wave. At the low end of the spectrum is short wave ultraviolet light, 100 nm. At the high end of the spectrum is long wave infrared, 1000 nm. In the middle of the spectrum are the wavelengths that plants use for photosynthesis, 400 nm – 700 nm.
This range of 400 nm – 700 nm is referred to as PAR. PAR is an abbreviation of photosynthetically active radiation.
Across the range of PAR, there are different wavelengths of light. We see these wavelengths of PAR as colours like this:
Wavelength patterns are not the same for every light. For example, a hospital light emits a bluish hue because it outputs more blue wavelengths than red, while a street lamp emits an orange hue because it emits more red wavelengths than blue.
Horticultural lights output unique wavelength patterns that can target a plant’s photoreceptors, stimulating optimal growth, and also influence if they direct their energies towards root growth or top growth.
The chlorophylls in cannabis that power photosynthesis capture light at specific wavelengths. The chart below shows the wavelengths where chlorophyl gets captured. Maximum absorption of chlorophylls a and b occurs between 430 – 453 nm (blue) and 642 – 662 nm (red). Horticultural lights often feature high output of these specific wavelengths to target the chlorophylls.
Chlorophyl light absorption peaks at 430 – 453 nm and 642 – 662 nm. To cater to the chlorophylls, some horticultural lights output almost all their power on these wavelengths. Their partial output pattern is represented in the chart below. The light output by these fixtures looks purple due to very high output of red and blue wavelengths, combined with very low output of green wavelengths.
Although partial spectrum lights can be used to successfully grow cannabis, evidence suggests better results are achieved with full spectrum light that includes red, blue and green light.
Green light has important special properties. Green light can penetrate the surface of the leaf, helping deliver energy to leaves under the canopy, and to the inner portion the leaves. Without green light, shaded leaves get deprived of energy.
Cannabis grows best under full spectrum lighting that includes green light, with extra output between 430 – 453 nm (blue), and 642 – 662 nm (red) wavelengths that target chlorophylls.
For production plants in their bloom phase, a full spectrum light that targets the chlorophylls and also has intense output on the red end of the spectrum works best.
When there is more intense red light, plants respond with greater top growth and stem elongation. These are the desired plant behaviours during budding.
Production plants in vegetative growth also grow best with a full spectrum pattern, but with extra intensity on the blue end of the spectrum. Blue wavelengths suppress the top growth promoting effect of the red wavelengths, allowing plants to focus greater energy on lateral root growth and branching.
When a blue biased wavelength pattern is used for vegetative growth, you can gain shorter, bushier plants with more roots.
A blue bias is also helpful for nursery plants because seedlings and mother plants should not be encouraged to grow tall. Root development and lateral branching are the most important objectives for them.
Nursery lights should be full spectrum with a heavy bias away from red.
It’s not absolutely necessary to have separate wavelengths for both production growth stages. Any full spectrum light will work for both stages of growth provided it can deliver suitable intensity for the size of plant. Custom wavelength patterns are a performance optimization, not a requirement of life. If budget does not permit separate fixtures for vegetative growth and flowering growth, it’s best to use the full spectrum bloom wavelength pattern with the red bias for both growth stages. The effect of strong red light to boost budding is the most important benefit to be gained from wavelength optimization.
We recommend a two step process that will optimize your germination rates. For the 1st step, you will pre-soak your seeds directly in water for 24 hours. Then you will complete germination by folding your seeds in damp paper towels for approximately 48-72 hours. The 2 step process helps you get the highest germination rates from your seeds by providing ideal exposure to water, air and heat.
The goal of the 1st step, soaking your seeds in glasses of water, is for ensuring water penetrates your seeds’ hard outer shell barrier. Cannabis seeds in the wild naturally have a hard outer shell because they are shed in the fall and need to survive the whole winter before sprouting in the spring. Water must penetrate the protective shell and reach the embryo for germination to start. A 24 hour soak allows water to penetrate even stubborn seeds, to begin the process of germination.
If seeds are left in water for longer than 24 hours there is a chance they will get waterlogged and the embryos will drown. To avoid killing seeds, after 24 hours move them to damp paper towels instead. Damp paper towels continue to provide moisture which is critical for germination, and they also prevent drowning by allowing some air to reach the seeds as well.
Some growers use only the paper towel step for germination. This will work for most seeds. However, by adding a pre-soak at the beginning, our recommended 2 step process increases your germination rates because it does a better job at delivering moisture for your outlier seeds that have tougher than average outer shells.
Step 1: Pre-Soak Your Seeds In Water
Add water and seeds to clean glasses that have been washed and thoroughly rinsed with no soap residue. You can use tap water if you adjust pH to 5.8 and dechlorinate it first. Or you can use distilled water which is already pH neutral and has no chlorine. It’s best to add only a small amount of water because less water makes it easier to retrieve the seeds from the glasses later. Leave the water to stand until it reaches room temperature before you add seeds to it.
For higher germination rates, add kelp extract at a rate of 0.2 gram per gallon to the water. Kelp extract contains gibberellic acid which helps seeds germinate. Older seeds especially will benefit from adding kelp to the pre-soak water.
Seeds must be warm or else they won’t germinate. Place the glasses of seeds on a heat mat to add warmth, with a towel down on the heat mat first to prevent the bottoms of the glasses from getting too hot. Drape another towel over the glasses to trap in warmth and block light.
After 24 hours, remove your seeds from the glasses. Pour the seeds and water out of the glass, being careful not to lose the seeds in the process. If you filled the glasses shallowly, it shouldn’t be difficult to extract the seeds with your fingers. If you need to pour some water out of the glasses to get the seeds, do it over a bowl or use a strainer so the seeds don’t escape with the wastewater. When using your fingers to move the seeds be careful not to cause any damage to any taproots that have emerged. Move the seeds right away to damp paper towels
Step 2: Germinate Seeds In Damp Paper Towels
Prepare paper towels by folding them into small squares. Soak them with distilled water, or tap water that has been pH balanced to 5.8 and dechlorinated. The paper towels should be moist, but not waterlogged. The right level of moisture is when they are wet, but there is no pooling water, or water dripping off of them. If you need to get rid of some water give the paper towels a light squeeze.
Fold your seeds inside the folded damp paper towels and put the paper towels with the seeds into plastic bags. Leave the bags open to allow some air to get in.
A very small amount of excess water inside the bags is okay because it helps prevent the paper towels from drying out from evaporation. Not too much water though, because pooling water can cause your seeds to drown.
Next, fold the seed bags inside a tea towel, then place the tea towel onto a heat mat. The tea towel acts as a buffer, preventing excessive heat. The heat mat should keep the seeds at the ideal temperature of 20° – 26°C (68 – 78°F). Lower temperatures can stunt germination.
The damp paper towels should stay moist for up to 2 days, which is usually enough time to complete germination. If the seeds need more time and the paper towels start to dry out, replace them with fresh damp ones.
All your seeds should be spouted and ready for planting within 48-72 hours in the paper towels. Check your seeds every 12-24 hours and plant them when the the tap roots are approximately 0.25” – 0.5”, (0.75 – 1.25 cm). If the taproot gets too long it is more difficult to plant, and more likely to get damaged. Transplant immediately when sprouts are the ideal length.
Prepare pots in advance so sprouts can be immediately transplanted once they are ready.
The ideal size pot for planting your seedlings is 4” size. Use 4” pots and not a larger size because a 4” size pot produces a plant with a tight root ball that is easy to transplant later. With a larger sized pot, you’ll get looser, more spread out roots, which are bad because they are prone to getting torn or damaged during transplant. Another benefit of 4″ pots is faster top growth. Small pots constrain plant roots which forces growth upwards. When their roots are allowed to expand their growth outwards a plants top growth is slower.
Pack pots with grow media. On the bottom of the pot, add a 1” layer of hydroton. Hydroton prevents water buildup on the bottom of the pot and creates air pockets so roots get access to air. Fill the rest of the pot with coco coir.
Pre-water the coco coir with distilled water, or tap water pH balanced to 5.8 prior to adding sprouts to the pots.
To plant your sprouts, first make a hole in the coco coir to plant your sprout in. The end of a tube is a good tool for this. The hole should be deep enough that your sprout’s tap root fits all the way inside. Drop your sprout into the hole using your fingertips so its tail is positioned down. If you miss, and the tail isn’t pointing down, it’s usually better to leave it misaligned than keep poking at it and risking damage. The tail will naturally revert itself and point back down on its own as it grows longer.
Gently backfill the indent with the coco coir until your sprout is completely covered. It shouldn’t be buried that deep, no more than 0.25” (0.635 cm) of medium on top.
Water & Nutrients For Seedlings
Water pots using a watering can with a wide distribution and slowly pour until water starts to drain out the bottom of the pot. When it starts to drain out the bottom you’ll know you’ve added enough water. Do not add water past the point it starts draining because an over saturated medium will suffocate sprouts.
Remember the weight of the pot when it is fully watered so later you can pick it up and judge if it needs more water or not by how heavy it feels. As a general guideline, plan to water every 2 days at first, then switch to every day when your seedlings get bigger. Never water past the point it starts to drain out the bottom.
For the initial watering use distilled water, or tap water pH balanced to 5.8. Once seedlings appear and their first two baby leaves begin to yellow, begin adding fertilizer at the following concentration:
350 – 500 TDS
0.7 – 1 EC
During the first week of growth extra phosphorus in fertilizer is beneficial for seedlings.
The more branches there are on a plant, the more clones it will yield. Shorter, bushier plants with more branches make better mother plants than plants with long stems and fewer branches. To encourage more branch growth, transplant in 2” pot size increments as plants get bigger. For example, from a 4” pot to 6” pot, from 6” pot to 8” pot and so on. This technique constrains roots, which has the effect of forcing more branches to grow.
How To Know When It’s Time To Transplant
Without sufficient roots to hold it together, media will be loose and will fall apart during a transplant, causing unwanted root stress and damage. Before transplanting, check first to see if there are roots growing out of the drainage hole at the bottom of the pot. This is a good sign that roots are developed enough to handle a transplant. Another good sign your roots are mature enough is the diameter of the plant’s top canopy is wider than the diameter of the pot. The diameter of the canopy mirrors the diameter of the root ball, and a wide canopy suggests that the root system has developed to the outer perimeter of the pot.
Setting Up A Fresh Pot For Transplant
The first step for preparing a new pot is adding a layer of hydroton to its bottom. For 6” – 8” pots, use 1” of hydroton. For 10” and wider pots, use 1.5” of hydroton. Hydroton is added to the bottom of pots because it creates air pockets that help with drainage and provide plant roots with air access.
Fill the new pot with coco coir, with the outgoing pot nested inside it. Pour a mix of 90% coco coir, 10% hydroton between the old and new pots, saturate it with treated water, then push it down with your fingers until it feels firm.
Remove the old pot using a twisting motion. The coco coir in the new pot will have a convenient indent ready to receive a new rootball.
Performing A Transplant
Secure the stem of the plant you are transplanting between your fingers, and its base with your palm. Then flip the pot upside down. The plant might simply fall out into your palm. If it doesn’t, with your other hand push your finger into the drainage hole at the bottom of the pot to dislodge the rootball. The rootball should come out as one piece with little mess.
Once the plug is removed from the old pot, drop it into the indent in the media in the new pot. Perform the transplant quickly because roots shouldn’t be exposed for any length of time.
Add some additional coco coir to fill in any gaps. Pack the coco coir tightly around the rootball.
After the plant has been successfully moved to the new pot, add 1” of sand on top. The sand helps prevent insects from getting into the coco coir and laying eggs.
As a last step, lay down a layer of hydroton. Hydroton helps with even distribution of water and maintaining the integrity of the sand barrier. Without the hydroton, coco coir can float up over the sand during watering.
A mother plant should be a minimum of 3 1/2 months old before it is strong enough for a small harvest of clones.
If you want to keep a mother plant alive after taking clones from it, only remove clones from the bottom 1/3 of the plant. Only take what you need. Don’t cut off more of the branch than you have to. With modest removal, the plant will stay alive and regenerate afterwards. If you don’t plan to regenerate the mother, strip off the entire bottom 3/4 of the plant right to the stem. You can use the top 1/4 as well, but it will produce weaker, slower growing clones.
If you are planning to reuse the mother, at 3 1/2 months you should be able to take 6-9 clones, and at 4-6 months, 12-28 clones. These numbers are approximate. The exact number depends on a variety of factors, such as pruning techniques, transplanting techniques, and the genetics of the mother.
A mother plant can be re-used many times, repeatedly producing and regenerating clones again and again. After harvest, a mother will take 2-3 months to fully regenerate back to a state where more clones can be harvested.
For smaller mother plants, a 10″-12″ sized clay pot works well. For mothers that need to produce bigger clone yields, a 24″ pot will result in a much larger plant.
For small indoor farms, it’s easiest to work with smaller mother plants. Smaller mothers don’t take up as much room and offer the flexibility of maintaining several strains.
Mother plants must be kept in a perpetual state of vegetative growth to produce clones. Maintain daily light levels for 12 hours per day or higher, 16 is recommended.
Use a full spectrum light with emphasis on blue wavelengths, 400 nm – 500 nm. Blue light discourages stem elongation and encourages root growth. A large root system will lead to greater branching that can be harvested for clones.
Vegetative, moderate growth:
15,000 – 40,000 LUX
Vegetative, heavy growth:
40,000 – 70,000 LUX
Motherplant Water & Nutrients
To feed motherplants use a standard mineral fertilizer intended for vegetative growth.
Motherplants benefit from enhanced uptake of minerals, especially calcium. Amino Acid opens up ion channels, dramatically increasing how much calcium mother plants are able to absorb. Calcium makes plant cell walls thicker with more stored energy. More stored energy make cuttings more resilient with faster rooting. Amino Acid is an excellent bio stimulant choice for motherplants.