Your indoor cannabis grow with LED lighting technology is approaching a turning point: the flowering. Your cannabis plants have reached an interesting size, and you’re preparing to induce the flowering by changing the photoperiod. But how do these lights affect the development of the flowering? Is it true they can result in more productive and better-tasting crops? Join us and discover everything about LED lighting during the flowering of indoor cannabis plants.
Flowering of Cannabis
Cannabis goes through several stages during its life cycle. It begins with germination, followed by the vegetative growth phase, the flowering, and the ripening/harvest. The light and specific wavelength frequency used at every stage of growth are crucial for the final outcome. This is a delicate process where the transition between photoperiods should be done suddenly to avoid or reduce stress on the plant.
Cannabis strains can be divided into:
- Photo-dependent (feminized and regular): their flowering period begins with a change to a 12/12 hr light/dark cycle.
- Autoflowering: their flowering phase is activated at a certain point in their life cycle, regardless of the photoperiod.
When the time comes, the plant stops growing and dedicates all its energy to producing the inflorescences that will fatten up and cluster to form the well-known and longed-for buds.
How Long Does the Flowering of Cannabis Take?
The flowering period for photo-dependent cannabis plants can last between 8 and 9 weeks, although some strains might require a few more or fewer days.
Flowering impacts the development time differently for indicas and sativas, with the latter taking more time in their final phase.
Flowering Stages in Cannabis Plants
- Pre-flowering
Small white pistils appear on female plants, and pollen sacs form on male plants. It’s important to separate the sexes to avoid pollination and obtain “sinsemilla” cannabis. - Early Flowering
Small buds begin to form on the main branches. “Stretching” or “flowering stretch” can be observed, with the plants gaining some centimetres, and some even doubling in height and branching out more. It’s advisable to monitor both the remaining growing space and the nutrients during this stage. - Mid-Flowering
The buds become compact and filled with shiny droplets. The development of trichomes is essential for resin production and to achieve good levels of terpenes and cannabinoids like THC. - Late Flowering
At this time, the buds harden, reaching their maximum size. The pistils start to change color (from white to darker shades of orange or brown). The trichomes also shift from a milky to an orange/amber color, indicating maturity. - Ripening and Harvest
This is the last phase of cannabis cultivation, when buds reach their optimal size and THC concentration.
Phases and Contribution of LED Lighting
LED lighting technology has evolved significantly in recent years, to the point that it can easily match or surpass traditional methods like HPS lights in terms of performance and energy efficiency.
Let’s now analyze the impact of LED lighting on cannabis cultivation and its common uses to improve its effectiveness.
Pre-flowering (Weeks 1-2)
- Switch the photoperiod to 12 hours of light – 12 hours of darkness to start the natural flowering process.
- The first pre-flowers or pollen sacs appear. Time to separate the sexes.
- Start adding more phosphorus and potassium to aid in flower formation.
- Start using LED lighting with red light (620–700 nm) and blue light (400–500 nm) to stimulate the flowering.
- You can start using LED-specific fertilizers and supplements (like Pro LED by Pro XL) from the vegetative phase, increasing the dose during the flowering.
Early Flowering (Weeks 3-4)
- The first small buds appear.
- Flowering stretch occurs.
- Keep LED fixtures at a height of 30 – 50 cm (depending on their power) to control the stretching and ensure that the plants receive enough light.
- Use a lux meter to measure the actual light reaching the plants. Consider the area of light that your fixture covers.
- Increase the power if your LED lamp allows it (try a 50μmol increase per day until reaching 800-1000 μmol, and always monitor plant health).
- Reduce humidity to 40 – 60% to prevent mold. Keep the grow area well-ventilated.
- Start illumination with deep reds (670–680 nm) and far reds (720–740 nm).
Mid-Flowering (Weeks 5-7)
- Lower humidity to 45 – 50%.
- Watch the power of your LED lamp to avoid burns. LED fixtures emit less heat, so they can be placed closer to the plants.
- Increase the amount of phosphorus and potassium to promote flower growth, but avoid excess nitrogen as it can worsen the taste of cannabis.
- Continue using lighting rich in reds, deep reds, and far reds.
Late Flowering (Weeks 8-9)
- Buds reach their maximum size and THC concentration.
- Predominantly milky trichomes.
- You might want to move your LED fixtures slightly away, or reduce their power to avoid unnecessary light stress.
- It’s time to start irradiating the plants with UV light to boost resin production and increase THC content.
- Lower humidity to 40 – 45% to prevent the appearance of fungi on the thickest, most compact buds.
- Gradually reduce the supply of nutrients to facilitate the flushing of the roots in the next phase.
Ripening and Harvest (Week 9 and Onward)
- Most trichomes look milky, and some are amber. They’re the best maturity indicators for the buds and should be observed with a microscope or a similar device.
- Start watering with only water 10 days before harvest to facilitate the flushing of the roots.
- Reduce the temperature of your indoor grow to promote one last burst of resin formation and darken the colours of the flowers.
- Keep using the UV light, taking care not to burn the plants and taking appropriate measures for your own safety (use sunscreen, long sleeves, etc.).
- You can use a product like “flush” a couple of days before flushing the roots. This is a very important process that can determine the taste of your crop if you’ve used mineral fertilizers or bio-minerals. It is not as essential if you’re using biological fertilizers.
Specialized Full Spectrum LED Lights for Cannabis
LED lights have made great strides in the field of lighting technology for cannabis cultivation. From the first systems (specialized in a specific phase of the plant’s life cycle) to modern dual spectrum systems, there are different types of lamps to meet the needs of all growers.
- Full Spectrum LEDs: These cover the entire range of visible light, from blue to red, mimicking sunlight. They’re perfect for the whole life cycle, including the flowering. They’re versatile and easy to use.
- Dual Spectrum LEDs: Equipped with a regulator to adjust and customize the radiation in each plant cycle. With these, you can enhance the precision of the blue light during the growth phase, and the red light in the flowering stage.
- LEDs with built-in UV and Infrared Light: These include invisible radiations in their lighting range that provide a notable boost in cannabis cultivation, increasing flower and resin production and THC levels in the final result.
- COB (Chip-on-board) LEDs: These high-intensity LED lamps are integrated into a single chip, generating a powerful and uniform light beam, which is ideal for covering larger grow areas. They usually provide a full light spectrum. They are especially effective during the flowering phase as they lead to greater light penetration.
- Quantum Board LEDs: Panels with LED lights distributed on a wide board that emit light powerfully and continuously, avoiding hot spots. They are typically full-spectrum and are well suited for growers looking to reduce costs, as they’re designed to maximize energy efficiency.
- LED Bars: Individual modular installations used to reinforce the main lighting or expand the grow area. They’re usually specialized in growth or flowering spectrums.
To choose the most suitable lamp for your cannabis grow, we recommend checking out our article on LED lighting.
Ultraviolet LED Light and THC for Cannabis Indoor Cultivation
Scientific studies state that UV light is key for increasing resin and THC levels during the final flowering phase.
The principle is simple: the plant receives UV light that forces it to protect itself by producing more resin and cannabinoids, including THC.
There are three types of UV light: UVA (315 – 340 nm), UVB (280 – 315 nm), and UVC (100 – 280 nm). UVA is suitable during the flowering, and UVB during the last part of the same phase. UVC frequency should never be used as it could be harmful to health.
In any case, remember that these are powerful radiations that must be used with caution, ensuring body and eye protection (using special lenses, for instance).
LED vs. HPS Lights during Cannabis Flowering
A small comparison shows the effectiveness of LEDs in the flowering phase as compared to using HPS lighting:
- LED lights are more suitable for small spaces. They provide noticeably less heat than HPS lamps, which results in less stress for the plants.
- LEDs are more economical in the long run, while HPS systems are more costly due to their electricity consumption and cooling needs.
- LED lamps produce buds of better quality and flavor – HPS lights may yield a larger number of buds but with a lower terpene count (we’ll explain this below).
- LEDs last longer and maintain their effectiveness – HPS lights need frequent replacements, which creates an additional expense.
LED Lights and Cannabis Taste
LED lights in cannabis cultivation generate less heat. This is beneficial for preserving the natural terpenes of cannabis plants, which are molecules whose combination establishes both the fragrance and taste of the flowers.
Most of these molecules do well at a temperature below 27º. Beyond that, terpenes may start deteriorating until they evaporate if they’re exposed to too much light and heat, like those emitted by HPS lamps, which can affect the final aroma and taste of the harvest.
Summary and Recommendations
Flowering is a crucial part of the plant’s life cycle and needs maximum attention. Good LED lighting in cannabis cultivation can be very beneficial as it provides specific radiations for each phase of development.
Full spectrum LED lighting (or, even better, dual spectrum) is highly recommended.
We hope these references help you use this innovative and effective equipment with great possibilities. See you under the lights!
