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The Perfect Light Schedules For Autoflowering Cannabis

Growing autoflowering strains? In this article, we explore the ideal light schedule to help your autos produce the best possible harvests.

WHAT’S THE BEST LIGHT SCHEDULE FOR AUTOFLOWERING CANNABIS?

Autoflowering cannabis strains flower based on age, rather than a change to their light cycle. Nonetheless, providing your autos with the right amount of light remains crucial to ensuring the best possible harvest. Read on to learn all there is to know about lighting for autoflowering cannabis strains.

18/6 LIGHT CYCLE

Cannabis is a C3 plant, meaning it can absorb CO₂ for photosynthesis even during light hours. And since autoflowering plants have short vegetative phases and often grow shorter than photoperiod strains, you’ll typically want to give your autos at least 18 hours of light. This allows for robust growth, without overspending on energy. Your autos love light just as much as traditional photoperiod strains, they just don’t rely on it to begin bloom.

24HR LIGHT CYCLE

Some growers will even give their autos a full 24 hours of light, arguing that this helps maximise vegetative growth. Growers who stick to 18-hour light cycles, on the other hand, argue that this gives their plants a short “recovery” period that is essential for healthy growth.

There’s no real consensus on whether autos grow better under 18 or 24 hours of light, and we’ve seen growers achieve great results with both methods. To make up your mind, we recommend playing around with both variations and sticking to what works best for you.

WHAT ABOUT A 12/12 LIGHT CYCLE?

Some growers still decide to keep their autos under a 12/12 light cycle during flowering. And that’s fine, as autos grown in these conditions can still produce a fair harvest. Just remember that the buds you harvest under a 12hr light cycle will be noticeably smaller than what you’d get under a 18–24hr cycle. Some reasons you might consider keeping your autos under 12/12 include:

  • Heat concerns: If you live in a very hot climate, you might want to turn your grow lights off during the day to avoid overheating your grow room. In that case, growing your autos under a 12/12 light cycle—with lights on during the night—might be your best bet to avoid causing your plants heat stress.
  • Growing autos alongside photoperiod strains: If you’re growing autos alongside feminized photoperiod strains, you’ll likely have to place your autos in the same room as your flowering feminized plants, meaning your autos will only get 12 hours of light per day.
  • To save money: Running grow lights for 18–24 hours over a few months can get very expensive. If you want to grow autos on a tight budget, you might want to use a 12hr light cycle instead.

PERFORMING SOG WITH AUTOFLOWERS

SOG, or sea of green, is a cannabis training technique that can produce some great harvests. Rather than getting your plants to grow as large as possible, SOG involves growing several smaller plants in close proximity to form a uniform canopy that maximises light exposure and space.

SOG is a great technique to try with autos because it takes advantage of the naturally smaller stature of these varieties. While every grower will have their own technique for SOG, most will grow between 4–16 plants per m², depending on how big they let each plant grow.

Depending on the size of the particular strain you’re growing, we recommend using 7–10l pots and growing between 4–6 plants per m². This should make the most of your space and lighting while still providing your plants with enough airflow to avoid any mould issues. If you decide to grow more plants per m², remember to use smaller pots to control their size and avoid overcrowding your grow room.

A NOTE ON LIGHT SPECTRUM

Using the right light spectrum is super important when growing any type of cannabis plant, including autos. Because autoflowering plants have such short life cycles, you really want to maximise the quality of light, nutrients, and soil you give them.

As you might recall from science class, when you shine a light through a prism, it is broken up into different colour spectrums. Plants, which depend on light for photosynthesis, respond differently to these different spectrums. Like with a photoperiod cannabis strain, we recommend sticking to the following light spectrums:

  • 6500K blue light during veg: Blue light spectrums have been shown to encourage vegetative growth, helping cannabis plants grow short and stocky while minimising stretching.
  • 2700K red light during flowering: Red light spectrums are ideal for bloom because they encourage budding and a little bit of stretch, encouraging your plants to produce big, dense flowers.

EXTRA TIPS FOR GROWING GREAT AUTOS

If you’re new to the world of autoflowers, follow these simple tips for a better harvest:

  • Pick a high-yielding auto: Not all autoflowers are made equal, so be sure to pick a high-yielding strain if harvest size is important to you.
  • Plant in your final container: Up-potting cannabis plants always causes stress. Since autoflowers can go from seed to harvest in as little as 8 weeks, it’s best to avoid this kind of stress and always plant your seeds straight into their final pots.
  • Use an airy growing medium: This helps stimulate root and foliage growth.
  • Use LST: If you want to train your autoflowering cannabis plants, only use low-stress techniques. High-stress techniques like fimming, topping, and supercropping will end up doing more harm than good.

Growing autos? Click here to learn all you need to know about the right light schedule for autoflowering cannabis strains.

Best Light Spectrum to Grow Autoflowers

When growing autoflowering plants indoor we need to simulate the environment they naturally grow in. The environment includes humidity, temperature, and the most essential of them all: light.

Either you prefer light bulbs or LEDs, you need the right spectrum in each stage for optimum growth.

1. What is Light Spectrum?

The light spectrum is the different colors (aka wavelengths) a source of light can emit. Light is measured in nanometers (nm) and each nanometer represents a band of light (a band of light is a section in the color spectrum). Humans can see a small part of the spectrum, between 380 to 780 nanometers, which means we can only see the colors ranging from violet to red.

Even though it appears white, the sun is a full spectrum light source and contains the whole spectral wavelength. That’s why rainbows happen. When raindrops refract light into individual wavelengths you can see all the colors (visible to humans) that make up sunlight.

In nature, cannabis plants grow under the sun, receiving the whole spectrum of wavelengths. This means we have to provide the maximum amount of wavelengths possible for the best development of our plant.

Although it’s not essential, it is considered good to provide the best light spectrum to encourage plant growth.

Remember this is not a rule, you can grow your plant from seed to harvest with any spectrum or amount of light but this can seriously affect your harvest.

2. Light Spectrums in Each Stage

During the vegetative stage, cannabis in the wild needs blue wavelengths to grow strong, big, and promote leaf growth. When growing indoors we aim to grow as many leaves as possible. With more leaves, there is more surface to absorb light, this way we ensure our plant develops a strong stem and branches preparing her for the flowering stage.

When entering the flowering stage, cannabis in the wild uses red wavelengths to promote bud formation. If we want to produce dense buds and increase yields we need to provide the plant red wavelengths, this will increase the rate of photosynthesis thus increasing bud formation.

• Tip: When experimenting with training, using “red” light will make plants grow taller, making it easier to train.

The general rules are “blue” light = shorter and stronger plants with more leaves, “red” light = taller and weaker (when compared to plants grown under “blue” lights) plants with fewer leaves.

3. Types of Light

Grow lights are usually divided into two kinds, light bulbs, and LEDs.

Light bulbs emit a limited scope of wavelengths meaning there are colors of the spectrum they don’t emit, therefore they are narrow-spectrum lights.

LEDs emit almost all the colors in the spectrum, they are composed of blue, red, and white diodes allowing them to emit all the wavelengths of the spectrum, therefore making them full-spectrum lights.

Light Bulbs: HPS, MH, CFL, and HID

Light bulbs come in four types: Metal Halide (CMH), High Pressure Sodium (HPS), Compact Fluorescent Lights (CFL) and High Intensity Discharge (HID).

MH bulbs are rated around 6500 Kelvin and are usually used in the vegetative stage because they emit a “blue” light (aka colder light).

HPS bulbs are rated at 2000 Kelvin are usually used in the flowering stage for their “red” light (aka warmer light).

CFLs are rated at around 5000 Kelvin, they emit a very weak “blue” light and are only used with seedlings and clones as they just need to develop roots for the first couple of days when the vegetative stage begins they should be transferred to a growing space with stronger lighting.

HID can cover from 3500 to 5000 Kelvin, they are similar to HPS but contains xenon inside, thus emitting a different spectrum and are more efficient while being more compact.

• Tip: You can also grow your plants under both CMH and HPS bulbs, this is called a mixed spectrum and will ultimately result in a better harvest.

Pros:

• Cheaper than average LED lights

• You don’t need to change the whole fixture, just replace the bulb

Cons:

• Electricity cost is higher if compared to LEDs.

• Need extra equipment for cooling.

• Requires changing bulbs (CMH to HPS) when entering the flowering stage.

Full Spectrum LEDs, and Infrared and UV Lights

All LEDs are full-spectrum lights unless advised, they may not contain all wavelengths but will emit the needed amount for each stage, unlike light bulbs, you won’t have to change anything other than your timer when you’re about to enter the flowering stage.

You can find full-spectrum LEDs that have UV and infrared diodes, if not, there are LEDs designed to emit those spectrums. They’re not that common in indoor growing but are said to benefit growers.

Just like everything else on the planet, cannabis plants are damaged by too much UV light but at the right amount. It can promote trichome production as the cannabis plants produce trichomes to protect itself from too much light.

As UV lights, infrared lights can harm your plants in excess but at the right amount, it can boost photosynthesis, affect yields, plant growth, and plant health in a positive way.

Pros:

• Used on the entire life cycle.

• Longer lifetime than bulbs.

Cons:

Note: It’s unusual to have UV and Infrared lights, they’re expensive and are NOT essential for growing good flowers. They’re recommended for more experienced growers who want to experiment with different spectrums.

4. Light Spectrums for Autoflowers

As most of you already know cannabis plants have two stages: the vegetative stage, and the flowering stage, needing a different light schedule and spectrums in each one of them.

Unlike photoperiodic, autoflowering plants start their life cycle in the flowering stage and depend solely on age to start producing buds. That’s why we recommend using a mixed spectrum of warm and cold light bulbs (CMH and HPS) or a full-spectrum LED during the whole lifecycle of your autoflower.

This way your plant will receive a complete spectrum of light guaranteeing the best flowers and biggest yield.

5. In Conclusion

The light spectrum is a small part of a much bigger system, there’s nothing as better light for your plant. But remember, the final product does NOT depend solely on your light.

Depending on which type you choose, either an LED or bulbs, you’ll have to adjust your growing environment accordingly to guarantee the best result possible.

When growing autoflowering plants indoor we need to simulate the environment they naturally grow in. The environment includes humidity, temperature, and the mos