Cannabis Light Stress And Light Burn
Dealing with cannabis light stress and cannabis light burn can be very stressful – especially if it’s your first time going through it. However, with the right precautions and growing know-how, it’s possible to identify light stress and bounce back even from the worst cases! Let’s learn how to do it.
What Is Cannabis Light Burn And Light Stress?
Cannabis light burn is the extreme case of cannabis light stress, which occurs when your plant gets more light than it needs for healthy growth. This can lead to bleaching of certain parts of the plant such as the leaves and flowers. However, light stress/burn can manifest itself in many ways, including the browning and drying out of leaves, giving them a dry, crispy texture.
Depending on your light source, there are different levels of associated danger from light and/or heat stress. Depending on how much heat your lights emit, the safe distance to hang them depends partly on the former factor as well as others such as plant maturity, level of airflow and type of light (HPS, CFL, LED, etc.). Before starting any grow, it’s therefore important to ensure you’ll be in a position to provide your plants with exactly the right conditions in which to properly grow.
Dangers Of Cannabis Light Burn At Various Stages Of Lifecycle
Simply put, the dangers of cannabis light burn are loss of potency, a worse appearance due to burning, and loss in quality and depth of terpene profile. Of course, the biggest danger would be a significant reduction in final yield.
The impact of light burn varies depending on the maturity of the plant, but this is the biggest issue for seedlings that can be easily burned by the high intensity of high-power growing lights. Next are plants in the vegetative stage which have established their ground and are self-supporting but are still susceptible to the dangers of powerful lighting. With respect to recovery, the greatest danger is for plants in the flowering stage, where it’s easy to overlook the impact of light stress as your plants change into their fall colors.
Symptoms Of Cannabis Light Stress And Light Burn
The following are symptoms of cannabis light stress and light burn:
- Bleaching of buds
- Browning of leaves
- Leaves curling upward (“taco”-ing)
- Discoloration of leaves but veins are still green
- Irregular growth pattern
If your plants are receiving too much light and are under stress, they will exhibit some or all of the symptoms listed above.
Are There Ways To Fix Light Burn?
Unfortunately, if parts of your plant have experienced light stress, especially to the point of light burn, then no amount of TLC will be able to bring them back. However, it’s possible to take remedial action by making changes to the amount of light your plant receives to a safe level and not inducing any further unnecessary stress.
Avoiding Light Stress And Light Burn – Learn How Much Light Is Too Much For Cannabis
If you have the resource to invest in a lux meter, it is highly recommended you do so! Not only is this useful in assessing whether your plants are getting too much light, but it can also identify areas receiving insufficient light. This is particularly important for commercial growers, as it maximizes bud production. Lux meter readings are given in lux/m 2 and should fall in the following ranges based on plant maturity:
- Vegetative: 30,000 – 70,000 lux/m 2
- Flowering: 50,000 – 90,000 lux/m 2
Set The Correct Height For Your Lights
Also, if you don’t have a lux meter, but still want to avoid light stress, it’s important to set the correct hanging height for your lights, especially as modern growing lamps tend to have high power ratings that can easily cause damage to cannabis plants irrespective of maturity. To check if your lights are hanging correctly:
1) Test the level of heat on the back of your hand at canopy level.
2) If it’s irritating at all, lift the source of light higher, and repeat the same test.
3) Do it again until the temperature feels comfortable and not irritating.
While this may seem basic, it’s a tried and tested way of making sure your plants get the light they need without overdosing them!
Ran Out Of Height? No Problem!
Ideally, one should never encounter this problem. With the right amount of planning, it’s possible to ensure your plants never grow too large for your space. However, things don’t always go to plan – especially when growing a plant from seed. If you’re limited for height, use low-stress training from 3-4 weeks into plant growth.
If your plants are growing too close to your lights and you don’t have any vertical space left to raise them, you can supercrop the plants to stunt their growth and keep them intentionally small. While supercropping is useful for this, it can also be used strategically to boost THC levels! This occurs when cannabis plants ramp up production of THC as a defense mechanism whenever they feel under attack.
Small Cannabis Plants
Here are some frequently asked questions that may help you better understand light burn.
How long does it take cannabis to recover from light burn?
While the damage brought on by light burn is permanent, your plant can still recover. Depending on its maturity, a plant may have enough remaining time in its lifecycle to recover from damage, whereas for plants that experience light damage toward the end of their life, there is very little that can be done. As long as you catch the problem while it’s not too late, cannabis plants can recover from light stress in as little as 5-7 days, although most plants take around 10 days to show physical changes.
Can light stress cause cannabis plants to change sex?
Cannabis plants can change sex as a result of environmental factors, and light stress is no exception. Plants that experience light/heat stress therefore have a far greater likelihood of turning into hermaphrodites than those that don’t, so it’s entire possible for this to occur as a result of light stress.
The following symptoms can cause cannabis plants to change sex:
- Changes in photoperiod
- Changes in temperature
Light burn or nutrient deficiency – how do I know?
When something goes wrong during a grow, most growers think about water or nutrient-related issues. If you think your plants are experiencing light burn, how do you know it’s not a nutrient deficiency? Well, while the symptoms of the two can appear to be very similar, it’s possible to easily tell between the two by considering the symptoms your plants are showing. It’s unlikely you’ll experience light burn-like symptoms due to excess of any of the nutrients described below, but it’s a possibility nonetheless (particularly with phosphorus).
This Is Not Light Stress But Nitrogen Deficiency, If…
- You notice discoloration of leaves (starting from the bottom of plant and moving upward)
- Leaves have droopy appearance without luster
- Leaves falling off (coming off without much resistance)
This Is Not Light Stress But Calcium Deficiency, If…
- You see irregular, yellow-brown spots on leaves
- Lower leaves start curling
This Is Not Light Stress But Phosphorous Deficiency, If…
- Leaves have blue/green tinge
- There are dark, copper-colored patches on leaves
- Leaves wither and curl at the tips
This Is Not Light Stress But Magnesium Deficiency, If…
- You notice the loss of older leaves (withering and dropping)
- Leaf veins turn yellow
- There are irregular rust spots
If you’re concerned about nutrient deficiencies causing changes in the appearance of your plant, flush the rootzone with 15-20 liters of plain, pH’d water to remove any build-up at the bottom of your growing medium.
Marijuana Light Burn And Stress: The Bottom Line
Let’s consolidate what we’ve learned. After reading about light stress and the dangers of light burn to cannabis plants, you should know what to look out for when assessing whether your plants might be receiving too much light. If you want to harvest large, dense buds with a beautiful appearance and fragrant terpene profile, ensure your plants are free of any signs of light burn by checking them frequently. This should not only help avoid light burn, but also highlight any other problems through the extra attention!
Cannabis light stress & burn may seem innocent, but it can be deadly to your harvest. Read on to learn about dangers of light stress in weed and how to avoid and fix it.
How To Spot And Treat A Light Burn On Your Cannabis Plants
Although not fixable with a nutrient solution boost, this is a problem that your plant can survive easily. As long as it’s not too late, after this article, you’ll know how to fix it.
This is a problem faced with indoor plants only. If you have an outdoor grow operation and feel your cannabis plants are suffering from light burn, forget it! You’ll probably want to look into other conditions that can show similar symptoms. The sun is too far out to damage your outdoor plants. Cannabis has existed for longer than the human race. It has developed well enough to handle the sun’s heat and light.
Light burn will only happen to an outdoor plant in a specific situation. It might happen if you grew it in the shade and just now transferred it into the light. In cases like this, the plant won’t be used to the heat and light and will eventually die.
WHAT IT IS AND HOW TO IDENTIFY IT
• Bleached Buds
One surefire symptom of light burn is bleaching of the flowers. This phenomenon occurs when flowers are located too close to high-powered lights. You may have seen images online of pure white “albino” cannabis flowers. This might look like the intentional development of rare genetics, but the fact is, most of the time this is simply bleaching. Luckily, it’s very hard to miss your flowers turning bright white.
Although white buds may look interesting, most of the time they have been rendered useless. The heat degrades cannabinoids present in the resin, which causes buds to lose potency. The scent and taste of these buds will also be less than desirable. The terpenes responsible for these traits are highly volatile aromatic hydrocarbons, and excess heat will also cause them to degrade.
• Yellow Leaves
Yellow leaves are another sign that your plant is being subject to light burn. However, yellow leaves can also signify nitrogen deficiency. The difference is that yellow leaves caused by this nutritional deficiency start from the bottom of the plant, display significant wilting, and will either fall off or are extremely easy to remove. On the other hand, yellowing caused by light burn will occur at the top of the plant, and these leaves will be much sturdier and harder to remove.
HOW TO SOLVE IT
The first thing you should do is move your plants a bit further away from the lights. This can either be done by moving the plants or by moving the lights, if you have the space. Take into consideration the most affected areas of each plant when choosing a new location for them. You can also remove some of your lights. If you have these well organized, it shouldn’t hurt your plants to remove a few bulbs.
If reducing the light or moving the plant isn’t an option, you can always low stress train your plants. This is a technique for obtaining more yields, where you try to keep the plant’s branches all at the same height. As the stem gets taller, it should be bent sideways and kept in that position with an external aid.
Try decreasing the temperature of the room too. Do this very slowly and always keep the temperature consistent. The plant will need time to adjust. Any change you’ll need to make to a plant’s environment or medium needs to be done carefully and patiently. It won’t matter how well you water and feed your plants, if you don’t take proper care of the environment, the plant will die.
HOW TO PREVENT IT
Growers can also utilise a lux meter to measure how much light different parts of their plants are being exposed to. These devices are used to measure lux, the unit of illuminance, per metre squared. They are handy as they offer readings regarding the intensity of light beaming down on any given area. Lux meters are ideal for hobby and small-scale growers as they are leagues cheaper than other light-measuring devices on the market. Growers can use them to determine if their plants aren’t getting enough light to produce an optimal yield, or if they are getting too much and are at risk of light burn.
A general healthy range for cannabis plants is between 35,000–70,000 lux during the vegetative phase and 55,000–85,000 during the flowering phase. If you notice any of the symptoms above and your lux meter is giving readings above these values, move your light source further away from your plants to reduce the intensity.
This can be a very hard problem to fix if not done in a timely manner. Be sure that you're informed about it if a light burn ever happens to you!