Light burn is a common problem for cannabis growers, but luckily it can be prevented if you know what to look out for. You’ll want to make sure that your light is at the right height and intensity level. This article will cover all of the symptoms, solutions, and prevention methods when it comes to light burn and help you grow healthy plants.
What is light burn?
Light is the most important factor in cannabis cultivation as it’s what drives photosynthesis and it’s how the plants make their food. The light can, however, also be a problem for your plants if you’re not careful. Light burn on cannabis is an issue that many growers run into at some point or another, but there are ways to prevent and fix it.
Light burn is exactly what it sounds like. It means that the plant has been exposed to too much light and is actually getting burned. The leaves will appear dry, brown, crispy, or wilted. Some parts of the leaf may even turn completely white as well. What happens to the plant when it gets light burn is that the photosynthesis process has been disrupted by too much light. Think of it like a person with a sunburn who’s trying to study for an exam or just go about their daily business, they can’t because they’re in pain and need time to heal. Naturally, taller plants are more likely to suffer from this as they grow towards the light source and it sometimes can not be moved higher which will eventually cause burn in cannabis plants. Don’t worry, we’ll show you how to fix your plant below so it’ll be back to normal in no time.
What are the symptoms of light burn?
There are several symptoms to monitor to determine if your plant has light burn. The most common signs of light burn being:
- yellow leaves or yellowing leaves with it starting at the tips of the leaves closest to the light
- Dry, brown, or crispy leaves on your cannabis plant and they will be most prevalent at the top of the plant closest to your light source if it’s an issue with overexposure
- White spots can appear where damage has been done to tissue by too much light white cannabis
- Some of the leaves may wilt and curl down toward the stem, though this is more common for heat burn than light burn (more on that below)
- Leaves will appear healthy at first but then start to lose color over time after being exposed to too much light because the photosynthesis has been disrupted so the leaves are starving
- Leaves will start to fall off of the plant when it has been exposed to too much light, though this is less common for cannabis plants
Usually, the tips of the leaves closest to the light will start to yellow and burn first if it is light burn.
How do I fix light burn?
There are several things that you can try to save your plant in case of an issue with too much exposure to the grow lights. Here is a list of solutions for fixing cannabis light burn:
First, if possible reduce the light intensity to give them a break from source of light. Some lights have dimmers for this. If you have a fan, use it as an exhaust by pointing it at your plants and turning it on high. This will help cool down your plant from heat stress which can be confused for light burn. If the temperature is too hot then this could also cause issues with light exposure so keep that in mind. If you don’t have a fan, invest in one. They are relatively inexpensive and make a huge difference with temperature control, which can prevent issues like this, as well as humidity levels which will lead to healthier plants overall.
You could also try moving the light further away from your plant because too much light exposure is usually what causes light burn. If you’ve tried all of the above and your plant is still getting light burned then it’s time to pick up some nutrients and figure out which nutrient deficiency, and sometimes nutrient excess, your plant is suffering from at the moment.
What height should I keep my light at different stages of growth?
The best answer as to what height you want your grow lights at depends on a few factors, but mostly it comes down to the strain and type of light you’re using.
An LED light should be kept around 18″ above the top set of leaves when it’s in early growth stage, while a metal halide (MH) or high-pressure sodium (HPS) bulb should be about 24-30 inches above the plant during early to middle stage of growth for cannabis. Adjust your light to approximately 24-30 inches away from the top of your plants when they’re in their flowering stage. NOTE: Keep in mind that these are just general guidelines for cannabis so if you have a smaller or larger cannabis plant, adjust accordingly.
What’s the difference between heat and light burn?
Heat stress is usually indicated by dry or brown spots on your leaves (similar to what happens if you get too close to a campfire) but it will also make them feel soft. If you touch your cannabis plant lightly with your fingers and everything feels fine, but the leaves are crispy, then it’s probably light burn. If you have a hard time distinguishing between heat stress vs light burn, it’s best not to risk exposing them more as that could end up burning them even worse if they’re already getting too much light or heat.
Can I prevent light burn?
The most effective way to prevent this issue is by using grow lights that can be adjusted in height so you don’t have to worry about whether or not your plant will get burned. By adjusting them as needed and making sure they’re at a safe distance from your plants, you’ll be able to prevent it.
Even if the grow light is adjustable and there’s no risk of them getting burned, you should still avoid having lights too close to your plant because this will also damage your cannabis in other ways such as causing heat or humidity stress that can hurt growth and resin production.
What is low-stress training?
Another method of prevention is low-stress training (LST). Many cannabis growers practice low-stress training to help avoid light burn and also increase yield. Low-stress training uses the natural response of plants to bend and thus train them with little damage. By bending branches, they are trained to grow away from light sources which increase yields in small spaces by allowing more even light distribution. LST can be used on your both indoor plants and outdoor plants which receive direct sunlight.
Low-stress training is a great way to decrease light exposure and increase yield in small grow spaces without the use of additional equipment such as fans or air conditioning units, making it an easy method for beginners with limited funds.
Summary
Light burn occurs when a plant is exposed to too much light, causing damage on the leaves of the cannabis plant and eventually killing them if not fixed immediately. Yellowing starts on the leaves closest to the light and that is where you typically see light burn on cannabis plants. Taller plants are naturally more prone to light burn. Light burn can be distinguished from heat stress by touching the affected leaves with your fingers because they will feel crispy or burnt while heated leaves will feel soft. Low-stress training is a method of preventing light burn by bending branches to expose them away from the grow lights. Light burn can be prevented using adjustable lighting or low-stress training methods on your cannabis plants without any additional equipment such as fans and air conditioning units, making it an easy option for beginners with limited funds. The easiest way to fix light burn during an indoor grow is to adjust your lights. You can either dim them or move them further away, how far will depend on which light you are using. How far away you move your lights also depends on whether you are in the vegetative stage or flowering stage of the growing process.
Thanks for reading our articles about light burn. Should you have any other questions please see our other articles about LST, light height, and heat stress
To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.
We strive to help your plants thrive.
Recent Comments