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Cannabis light burn

Cannabis light burn: how to detect and treat

Cannabis light burn is a common issue for any cultivator. 

Providing enough light is a pillar of marijuana care. It’s vital for plant energy, food, and healthy development, yet it’s entirely possible to give your plants too much of a good thing. 

When marijuana light burn occurs, your crop will suffer the consequences of becoming stressed, damaged, and in some cases, no buds!

How do you prevent, detect, and treat leaf burn? Continue reading to learn all you need to know to ensure you don’t end up with burnt weed before it’s ready to be lit up. 

What is cannabis light burn

Cannabis light burn is a serious concern for indoor growers using artificial lighting. It happens when marijuana grow lights are hung too close to your plants, overexposing your pot to light and heat.

When light burn in cannabis happens during the flowering stage, it isn’t just the leaves that are affected. Buds turn white, which is a clear indication of severe damage.

The all-important cannabinoids, resins, and terpenes are also destroyed. The bud’s fragrance and flavor become non-existent, and they’re rendered ineffective for recreational or medicinal use. 

 Cannabis light burn
Marijuana plants at outdoor cannabis farm field

Cannabis light burn symptoms 

The symptoms of light burn on weed don’t appear overnight. In some cases, the lights are just a little too low, meaning that stress and burns happen gradually. 

It’s vital for the health of your marijuana that you don’t waste any time diagnosing cannabis light burn. Use our guide to symptoms below to get a clear understanding of what to look out for. 

Bleached buds and leaves

An obvious sign that your cannabis has too much light is bleaching of the flowers and leaves. The frosty ‘albino’ look is visually striking but is bad news for your bud. 

Bleaching typically occurs from LED light burn on weed.

Yellow leaves

Yellowing leaves are always a clear sign of ill health in marijuana. The tricky part is identifying if the discoloration is from too much light on the cannabis or nitrogen deficiency. 

Plants will show distress from the bottom, while cannabis leaf burn occurs at the top of the plant. 

Leaves pointing upwards

One of the earliest signs of cannabis light burn is upward-pointing leaves. The utmost set of foliage closest to the light source will curl to try and shade themselves.

Brown spots

In severe cases of marijuana light burn, leaves will turn from yellow to brown and feel crispy.

How to prevent light burn on weed plants?

The most effective way to avoid cannabis light stress is to properly position your lights from the get-go and be prepared to adjust them as your plant matures. The easiest way to do this is to install drop lights on a pulley system.

You can purchase grow lights with different light spectrums, wattage, intensity, and types of light. 

The best LED grow lights, and HPS setups will come with instructions for distancing, but if they don’t, use our charts below. 

LED 

Wattage Closest distance (inches) Farthest distance (inches) 
150 15 25
300 16 27
600 18 29
1200 22 31
2000 26 33

HPS

Wattage  Closest distance (inches) Farthest distance (inches) 
150 8 12
250 10 14
400 12 19
600 14 25
1000 16 31
1200 18 33

Other methods to prevent cannabis light burn include topping and tying down your weed using the Screen of Green (ScrOG) training technique.

Can you fix burns on marijuana plants?

Prevention is always better than the cure when it comes to cannabis light burn.

As soon as you recognize the sign of leaf burn, you must act fast. Move the grow lights further away from your plants and lower their intensity. 

You should then give your weed a deep watering to replace any moisture lost. A seaweed tonic will also help your plants retain the water. 

Pluck the damaged leaves off to stop them from further stressing the plant and consider installing a cooling system. 

If marijuana light burn occurs during the vegetative stage, the easiest way to bring your plants back to life is by topping them. 

 Cannabis light burn

Does light burn cause reproductive changes?

Marijuana plants are prone to switching genders as a survival tactic when subjected to poor environmental parameters. 

High levels of heat and cannabis light stress can trigger this change, making them hermaphrodites. 

They’ll produce seeds rather than flowers in this state, ruining your chances of a bountiful harvest of buds. 

How much light does a weed plant need? During the vegetative stage, your weed will need 18 to 24 hours of light; then, they’ll need much more balance throughout the flowering phase. Provide your crop with 12 hours of light and 12 hours of dark. 

Do not disturb this cycle, as doing so can significantly impact potential yield size, and your plants can even flip back into being vegetative. 

The difference between nitrogen deficiency and light burn

The easiest way to tell marijuana leaf burn from a nitrogen deficiency is by paying attention to where the leaves are affected. 

As nitrogen comes up through the roots, leaves at the bottom of the plant will yellow first, become limp, and fall off. 

Burnt weed shows symptoms on the upper leaves, which are closest to the light source. 

Foliage turns yellow or has a purple/red hue before becoming brown at the edges. To the touch, they’ll feel crunchy and are hard to pull off the plant. 

Pay close attention to the leaves’ veins as well. Burnt weed keeps its green veins while nitrogen-deficient plants don’t.

Take note that a nutrient-deficient plant will be more susceptible to leaf burn. Healthy marijuana is much more tolerant of their environments like heat and light. 

Heat stress and light stress

Often heat and light stress in cannabis come hand in hand. An infrared grow light system, for example, is notorious for emitting high levels of heat.

When lamps are hung too close, plants suffer from overexposure to light and heat simultaneously. 

In this scenario, typical cannabis light burn symptoms will arise alongside signs of stress, including wilting, discoloring, and eventually no nugs. 

You can check if your lights are beaming too much heat by placing your hand at crop level. If you can comfortably keep it there, then your plants will be safe. 

 Cannabis light burn

FAQ related to cannabis light burn

Check out our answers to the most commonly asked questions surrounding cannabis light burn below.

Is too much light bad for cannabis plants? 

It’s true cannabis craves light and needs it to develop healthily, but too much can cause serious problems.

Light stress in cannabis caused by high intensity, low hung lights, or a poor cycle can trigger ill health and reproductive changes. Terpenes and cannabinoids will also deteriorate in potency and flavor.

What do you do for light burn?

As soon as you spot signs of stress or light burn on weed, raise your lights

Give your weed a good watering to help it regain moisture and pluck off any severely damaged leaves. Consider adding a seaweed tonic into your feeding schedule to encourage your plants to retain water better. 

Can you burn plants with LED lights?

It’s a common misconception that LED light burn on cannabis doesn’t occur.

Although they run cooler than most other lighting systems, LED light burn is still possible when the lights are too close to your plants. Instead of burning the leaves and browning buds, they ‘bleach out.’

Can grow lights burn seedlings?

Seedling light burn is a very common beginner’s mistake. Young plants need plenty of light to grow strong, but their fragile leaves are sensitive. 

Make sure there’s plenty of distance between them and the lights to avoid burning. 

How to fix a burnt plant? 

Once you’ve spotted signs of burnt weed, work fast to move your lights to a better distance. Thoroughly water your plants, prune dead leaves, and start a schedule of seaweed tonic feeding. 

The final word

Light burn on weed typically occurs when your grow lights are too close to your plants.

It damages the leaves and destroys buds. It also causes cannabis light stress which can lead to reproductive changes. 

Prevent it from wreaking havoc on your crop by hanging them for efficient but safe light distribution and adjust the height when necessary. 

You can also apply training techniques as prevention, and an appropriate light cycle for weed will reduce the chances of stress. Follow our guide to overcoming cannabis light burn, and in return, you’ll have happy weed rewarding your efforts with premium-quality buds.