Sunburn on a cannabis plant is a severe form of light and heat stress, occurring when the plant receives too much light intensity, often compounded by high temperatures. This stress significantly impairs the plant’s ability to photosynthesize and grow, negatively impacting its overall health and potential yield. It is a common challenge for growers, particularly those cultivating plants outdoors or with powerful indoor lighting systems.
Recognizing Sunburn Symptoms
Identifying sunburn on cannabis plants involves observing specific visual cues, particularly on the upper leaves closest to the light source.
Affected leaves often display yellowing or a pale, bleached white appearance, especially at the tips and edges. This discoloration is distinct from nutrient deficiencies, as it typically begins at the top of the plant rather than the bottom. In severe cases, the affected areas may become crispy, brown, or even develop scorched spots.
Leaves might also exhibit “tacoing,” where the edges curl upwards, resembling a taco shell, or curl downwards in a claw-like fashion. This is an adaptive response by the plant to reduce the surface area exposed to intense light. Beyond discoloration and curling, stunted growth can occur as the plant redirects energy from development to survival.
Factors Causing Sunburn
Cannabis plants primarily experience sunburn due to an imbalance between light exposure and their environmental conditions. The most common cause is excessive light intensity, especially when plants are suddenly exposed to much brighter conditions. This often happens when grow lights are positioned too close to the plant canopy, overwhelming the plant’s photosynthetic capacity. Different types of grow lights, such as LEDs or HPS bulbs, can deliver intense light that, if not managed correctly, leads to damage.
High ambient temperatures significantly exacerbate light stress, as the combination of intense light and heat places immense strain on the plant. Inadequate air circulation around the plant canopy can further contribute to heat buildup, creating hot pockets where leaves are more susceptible to damage.
Preventing Sunburn Damage
Preventing sunburn damage requires careful management of light intensity, temperature, and environmental acclimation. For indoor growers, maintaining the correct distance between the light source and the plant canopy is important. Manufacturers often provide recommended hanging heights for their specific grow lights, which serve as a valuable starting point. Utilizing a light meter, such as a PAR (Photosynthetically Active Radiation) meter, can help accurately measure the light intensity reaching the plants, ensuring optimal levels for each growth stage.
Gradually increasing light intensity, especially when upgrading lighting systems or moving plants, allows them to adapt without shock. Many modern LED grow lights offer dimmer functions, enabling growers to fine-tune light output. Beyond light, temperature control is important; adequate ventilation, exhaust fans, and proper air circulation prevent heat from accumulating around the plant canopy. Maintaining a comfortable grow room temperature, ideally between 68-77°F (20-25°C), reduces overall plant stress.
For outdoor plants, acclimation is important when moving them from a less intense environment to direct sunlight. Providing partial shade during the hottest parts of the day, typically between 10 AM and 4 PM, can protect plants from peak sun intensity. Shade cloths are effective tools for outdoor cultivation, reducing the amount of direct sunlight without significantly impacting growth. Consistent monitoring of both indoor and outdoor conditions allows growers to make timely adjustments, proactively safeguarding their plants from potential sunburn.
Helping Plants Recover From Sunburn
Once a cannabis plant shows signs of sunburn, immediate action is necessary to facilitate recovery. The first step involves reducing the light intensity or increasing the distance between the light source and the plant canopy. For indoor setups, this might mean dimming the lights or raising them by several inches; for outdoor plants, providing temporary shade is beneficial. Simultaneously, lowering the ambient temperature around the plant helps alleviate additional stress.
Ensuring good air circulation through fans or improved ventilation helps dissipate localized heat pockets around the leaves. While damaged leaves may not fully recover their original appearance, new, healthy growth should emerge with proper care. It is important to provide adequate water to the plant without overwatering, as stressed plants can be more susceptible to root issues. Patience is also important, as plants typically require one to two weeks to show significant signs of recovery after adjustments are made.