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Dial in PPFD for flower to get the best results.

Tom Starley
April 26, 2024
11 min read
Grower dialling in PPFD for flower to get the best results
Grower dialling in PPFD for flower to get the best results
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When growing cannabis indoors, light is more than just a basic need, particularly when it comes to PPFD, which stands for Photosynthetic Photon Flux Density.

This crucial measurement illustrates the amount of light that reaches your plants, influencing every stage of their growth, especially the flowering phase. 

Understanding and adjusting PPFD for the flowering stage can mean the difference between a mediocre harvest and a new personal best. 

In this guide, we'll navigate the intricacies of PPFD, ensuring you have the knowledge to optimise your grow lights and achieve the best results for your plants. 

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

Get early access to the Grow Sensor now and dial in PPFD for flower to get the best results.

Understanding PPFD and its role in cannabis growth

PPFD, or Photosynthetic Photon Flux Density, plays a critical role in the growth of cannabis during other growth stages, but especially during its flowering stage. 

It calculates how much PPFD of light in photons that hit a given area every second. This metric is crucial because it directly influences the rate of photosynthesis.

Daily Light Integral (DLI) complements PPFD by summing up the total light received daily, giving insights into the plant's overall light exposure. 

This helps you understand and manage your plants' cumulative light exposure, ensuring it aligns with their needs.

Light spectrum also plays a pivotal role in how cannabis plants use PPFD. Different colours within the spectrum can trigger various growth responses. 

By understanding how PPFD, DLI, and the spectrum of light work together, you can create an ideal light environment that supports your plants' vigorous growth and flowering.

Measuring light intensity is crucial in optimising PPFD for flowering. Light meters, especially those specially calibrated for PPFD, help growers understand how much light their plants receive.

Whether you use an LED grow light or HPS lights, ensuring your cannabis plants get the right PPFD or intensity of light within the photosynthetically active radiation (PAR) range is essential.

An illustration explaining what PPFD is and how it can help you dial in PPFD for flower to get the best results.


The ideal PPFD for flowering cannabis

Finding the optimal PPFD for the flowering stage of cannabis is crucial for cultivating dense, potent buds. 

While the ideal PPFD can vary based on several factors, including strain and environmental conditions, aim for a range between 600 to 900 μmol/m²/s. 

This range provides sufficient intensity to drive photosynthesis. Growers looking to hit their plants with 700 μmol/m²/s plus should be looking to supplement their plants with CO2 to get healthy results. 

An illustration showing what to set your PPFD to when not supplementing with cO2,


Ideal PPFD ranges for different growth stages

Seedling growth stage PPFD requirements

In the initial seedling stage, cannabis plants need a gentle introduction to light. The perfect PPFD level for seedlings falls between 100-300 μmol/m²/s.

Vegetative growth stage PPFD needs

As you transition into the early vegetative stage, your plants’ capacity for light absorption heightens, requiring a PPFD between 200-400 μmol/m²/s. This range fosters the development of robust leaves and promotes stem growth, which is crucial for building a solid foundation for future growth phases.

Advancing to the full vegetative stage, the need for light intensifies, with PPFD levels recommended to be 400-600 μmol/m²/s. This boost in intensity is necessary for maximising photosynthesis, propelling the plants into rapid and healthy expansion, and preparing them for the forthcoming flowering stage. 

The best PPFD for flower

The flowering stage sees a significant jump in light requirements, with PPFD levels best set between 600-900 μmol/m²/s. This higher intensity of light is key to developing dense, resinous buds, driving the plant's reproductive efforts. 

For the best results, especially in terms of bud quality, aim for the higher end of this PPFD range, ensuring that other grow room conditions like temperature and CO2 are also optimal.

Late flowering considerations

As the plants approach harvest during the late flowering stage, maintaining high PPFD levels remains important for the final maturation of the flowers. However, monitoring your plants closely for any stress indicators is essential. 

Excessive light intensity in these final stages can harm the delicate buds, potentially impacting the overall quality and yield.

An illustration showing what to set your PPFD to when supplementing with cO2,

Adjusting PPFD throughout the flowering stage

Adjusting PPFD during flowering is a careful balancing act that can significantly influence the final results of your harvest. 

As your plants transition from vegetative growth to flowering, their light requirements evolve. Initially, a PPFD for early flower around 600 μmol/m²/s is a good starting point. 

As the flowering phase progresses, gradually increasing the PPFD ensures your plants have the energy they need. 

Midway through the flowering stage, aiming for a PPFD during flower of around 700 to 800 μmol/m²/s can promote more vigorous growth. 

In the final weeks, maintaining or slightly increasing the PPFD to around 800 to 900 μmol/m²/s can help maximise resin production and bud density.

It's essential to monitor your plants for signs of light stress, such as leaf bleaching or curling, which may indicate that the PPFD is too high. 

Remember, the goal is to mimic the natural progression of the sun's intensity over the growing season, providing your cannabis plants with a tailored light environment that encourages robust flowering.

Get early access to the Grow Sensor now and dial in PPFD for flower to get the best results.


The impact of light spectrum on PPFD

Light spectrum plays an important role in how effectively PPFD is used by cannabis plants, particularly during the flowering stage. 

While PPFD measures the quantity of light, the spectrum provides the quality, offering the different wavelengths that plants use for different growth processes. 

The spectrum of light, including green light and the broader range of visible light, plays a significant role in plant development.

Red light is paramount during the flowering phase, falling within the 620 to 750 nm wavelength range. 

It encourages bud formation and helps increase the density and improve the quality of the cannabis flowers. However, this doesn't mean other parts of the spectrum should be neglected. 

Blue light (450 to 495 nm) is more crucial during the vegetative stage for promoting healthy leaf growth. But it still contributes to a well-rounded light spectrum that supports overall plant health and development.

Growers often choose LED grow lights because they provide a balanced spectrum that can be adjusted according to the plant's stage of growth. 

LED lights and HPS lights offer different spectra, affecting the plant's growth and photosynthetic active radiation (PAR) absorption. 

Understanding the light energy emitted by your grow light fixtures can really help you to optimise each growth stage.

An illustration showing the grower where to measure the ppf in the grow room to dial in PPFD for flower.


Measuring and monitoring light intensity

Consistent measurement and monitoring of PPFD are key. This is where an advanced light meter or specially calibrated sensor to provide accurate PPFD readings becomes an indispensable tool in your grow room. 

These tools measure light emitted in micromoles per square meter per second (μmol/m²/s), offering insights into how plants respond to light during their photoperiod. 

This data is essential for adjusting lighting to suit different growth stages and to ensure optimal development.

You can make informed decisions to adjust your lighting setup by accurately measuring the light intensity at the canopy level. You can ensure your plants receive the optimal PPFD throughout their flowering stage.

An illustration explaining that the grower needs to move there Grow Sensor up as the plants grow to make sure the ppf is accurate.

When measuring PPFD, take readings at various points to understand the light distribution in your grow space. This helps identify any hotspots or areas where light intensity may be too low. 

Adjusting your grow lights based on these readings leads to more even light coverage, ensuring all parts of your plants receive the light they need.

Regular monitoring allows you to adapt to the changing needs of your plants as they progress through the flowering stage. 

By closely monitoring PPFD levels with a reliable light meter, you can optimise light intensity for maximum yield and quality, making every photon count in your quest for the perfect harvest.

A grow room example w here to much ppf has been used and the plants are burnt.


Common PPFD mistakes and how to avoid them

Navigating PPFD during the flowering stage is fraught with potential pitfalls. 

One common mistake is providing too much light (too much PPFD), thinking that more is always better. This can lead to light burn, where leaves turn yellow or white, and the plant's health deteriorates. 

Aiming for slightly lower PPFD levels and ensuring you're within the optimal PPFD for flowering can prevent this.

Another issue is uneven light distribution, often overlooked by growers. Even with the proper PPFD levels, if the light isn't evenly distributed across the canopy, some plants may flourish while others won't. 

Using a PPFD meter to regularly check light distribution and make necessary adjustments to your lighting setup can protect against this.

Ignoring the light spectrum can also be detrimental. While focusing on PPFD during flowering is crucial, the light spectrum should not be neglected. 

A balance of red light and blue light, even during the flowering stage, supports overall plant health and contributes to the development of potent, resinous buds.

Not adjusting PPFD throughout the different flowering stages can hamper plant development. Gradually increasing PPFD as the plant matures ensures that your cannabis is receiving the right amount of light at each stage of its flowering cycle.

Lastly, carbon dioxide (CO2) levels in your grow space can influence how your cannabis plants use light energy. 

Higher CO2 levels can enhance your plant's growth under the right PPFD, making efficient use of the light produced by your LED grow light, ceramic metal halide lights or other light source. 

By being mindful of these common mistakes and adopting a measured, attentive approach to PPFD adjustment, you can optimise your light environment for the best possible yield and quality.

                         

A grow room with dialled in PPFD for flower.

        

Optimise your light cycle for maximum PPFD efficiency

Adhering to a 12/12 light cycle replicating the natural shift from summer to autumn signals your plants to enter the flowering phase. 

This period requires intense light, ideally with a spectrum leaning towards red light wavelengths, to boost photosynthesis and encourage robust bud formation.

Ensuring the PPFD aligns with this cycle and the light quality is suited for flowering can significantly enhance your yields. 

Daily light integral

Incorporating a Daily Light Integral (DLI) into consideration is also essential. Getting the right DLI and PPFD balance is key to mimicking optimal natural conditions for flowering.

In an indoor setup, factors like grow tent size and light fixture placement can greatly influence PPFD levels. 

Efficiently managed grow spaces ensure even light distribution, allowing for effective photosynthesis even at varying PPFD levels across growth stages. 

Additionally, enriching grow spaces with carbon dioxide can further enhance plant growth by improving their light energy usage, which is especially beneficial under higher PPFD levels. 

Combining CO2 enrichment with precise PPFD and DLI management can yield remarkable results, making every photon count.

A grow room with dialled in PPFD for flower. Its almost harvest time.


Case studies 

Recent studies have highlighted the importance of optimal PPFD levels during the flowering stage of cannabis cultivation, highlighting its impact on yield, quality, and overall plant health.

One study conducted by researchers, including the involvement of Texas Original Compassionate Cultivation (TOCC), explored the effects of high light intensities on cannabis, with PPFD levels ranging from 1,000 to 2,500 μmol/m²/s. 

They discovered that yield increased significantly with light intensity up to 1,800 μmol/m²/s, beyond which the benefits began to diminish. 

Surprisingly, even at these high intensities, the cannabis plants showed no signs of phototoxicity, indicating their high tolerance for light. 

This research suggests that cannabis can handle and even thrive under high PPFD levels without adverse effects as long as the increase is gradual and other environmental factors are controlled​​. 

Another study published in Frontiers in Plant Science found that the dry inflorescence yield of cannabis linearly increased with canopy-level PPFD up to 1,800 μmol/m²/s. 

The study also observed that the density of the apical inflorescence and harvest index improved with increased light intensity, resulting in higher-quality marketable tissues. 

Interestingly, there were no significant effects on cannabinoid potency with different light intensities, indicating that while higher PPFD can boost yield, it may not necessarily enhance the potency of the cannabinoids​​. 

These findings emphasise the critical role of PPFD in maximising cannabis yield during the flowering stage, underscoring the need for growers to manage light intensity to optimise their cultivation practices carefully.

The Grow Sensor and App ready to help you Dial in PPFD for flower.


Use a Grow Sensor to grow better plants

Using a Grow Sensor in your cultivation setup can revolutionise your approach to plant care, providing a strategic advantage. The Grow Sensor grats give you immediate insight into crucial environmental factors within your grow area 24/7.

By continuously monitoring essential conditions like your lights’ PPFD output from your light, humidity, temperature, and CO2 levels, you're always in the know.

This critical information enables you to fine-tune your grow, ensuring your plants receive the exact light intensity required at every stage of their growth. 

Further benefits of the Grow Sensor include:

  • Monitoring of Vapour Pressure Deficit (VPD).
  • Daily Light Integral (DLI) calculations to track cumulative light exposure, ensuring your plants get just the right amount of light each day.
  • A full spectrum PAR meter.
  • Leaf Surface Temperature (LST) readings are used to check on plant well-being, which directly indicates environmental stress or comfort.
  • Dew point readings to avert humidity-related complications, safeguarding your plants against mould and mildew.
  • Integration with the Grow soil probe, which measures critical soil parameters like EC, moisture levels, and root zone temperatures, offers a comprehensive view of your plant's growing conditions.
  • Key metrics for implementing advanced crop steering methods.
  • Offline data storage feature for easy record-keeping and historical analysis of your crop's progress.

With a Grow Sensor, you can precisely dial in your growing conditions, leading to healthier plants and significantly larger harvests.

A PPFD sensor measuring the PPFD at the canopy.


Takeaways

Mastering PPFD for the flowering stage of cannabis cultivation is a game-changer for any grower looking to achieve unmatched quality and yield. 

By understanding and implementing the optimal PPFD levels, adjusting light intensity as your plants progress through their flowering stages, and maintaining a conducive light spectrum, you set the stage for vigorous plant growth and potent bud production.

Remember, the key to leveraging PPFD effectively lies in monitoring and adjustments. 

Regular use of a PPFD meter to track light intensity ensures your cannabis plants are always receiving the right amount of light without the risk of light burn or underexposure. 

Coupled with a keen eye on light cycles and spectrum adjustments, you can truly optimise your grow room's lighting environment.

As you embark on this journey, keep in mind that every cannabis strain and grow room environment is unique. What works for one setup may need tweaking in another. 

Experimentation and careful observation are your best tools in dialling in the perfect PPFD for flowering, leading to a bountiful harvest of top-tier cannabis.

Happy Growing!

FAQs

What is the recommended PPFD for flowering plants?

The recommended PPFD for flowering plants is between 600 to 900 μmol/m²/s. This range supports optimal growth and bud development during the flowering stage.

Is 1000 PPFD too much?

A PPFD of 1000 μmol/m²/s is not necessarily too much, but you will need to have a fully dialed-in controlled environment. Some studies have shown that cannabis plants can tolerate and even thrive under high PPFD levels up to 1,800 μmol/m²/s without adverse effects, given a gradual increase and proper environmental controls​​. 

What is the minimum PPFD for photosynthesis?

The minimum PPFD for photosynthesis, also known as the light compensation point, varies by plant species but is generally around 50-75 μmol/m²/s for many plants. At this level, photosynthesis just compensates for respiration, allowing for minimal growth. It's essential to ensure that PPFD exceeds this threshold to promote healthy plant growth​​​​.

What happens if PPFD is too high?

If PPFD is too high, it can lead to light stress in plants, manifesting as leaf bleaching, curling, or burning. This stress can overwhelm the plant's photosynthetic capacity, leading to damage and potentially reduced growth or yield​​​​​​.

A burnt cannabis flower that has received  to much PPFD.


What is the PPFD value of sunlight?

The PPFD value of sunlight can vary widely depending on factors like the time of day, weather conditions, and geographic location. In many regions, sunlight can range from about 800 to 2,000 μmol/m²/s under clear sky conditions at noon.   

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Tom Starley
April 26, 2024
11 min read

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