In this growshopweb.com blog article, we will discuss a very common issue: marijuana leaves that develop yellow or brown spots.
Our content is purely informational: we do not sell marijuana containing THC nor do we encourage its consumption.
In our store, you will find only fertilizers, nutrients, substrates, measuring instruments, pest control products, and everything needed for responsible home cultivation.
What are the yellow/brown spots on marijuana leaves?
When yellow marijuana spots appear or when certain areas darken into brown cannabis leaves, the plant is signaling a problem.
These marks may be caused by a cannabis nutrient deficiency, irrigation issues, improper pH, excessive light exposure, fungal marijuana spots, or pest attacks.
A proper diagnosis of damaged marijuana leaves is essential to restore the plant’s health.
This blog provides general guidance for growers. Each cultivation environment is different, so it’s important to observe carefully, adjust parameters gradually, and avoid panic.
The role of calcium in the cannabis plant
Calcium is present throughout the plant and is essential for many processes, especially growth.
It acts as a cellular regulator and contributes to the plant’s overall stability.
The plant has two internal transport systems: xylem and phloem. Calcium circulates almost exclusively through the xylem, which makes it a low-mobility element within the plant tissues.
For this reason, it is crucial to ensure a constant supply of calcium in the root zone.
When calcium is lacking, yellow marijuana spots with brown edges may appear, along with leaf deformities or necrosis.
This type of cannabis nutrient deficiency often begins on new or intermediate leaves and can spread quickly if not corrected.
What are the visible symptoms of calcium deficiency?
- Yellow/brown spots surrounded by a dark brown edge.
- Leaf tips that are burned or dry.
- Slow growth and weak structure.
What to do in case of calcium deficiency?
The most common solution is to add calcium using a calcium nitrate fertilizer or a CalMag supplement.
At growshopweb.com, you will find fertilizer lines and calcium/magnesium additives designed to correct this type of cannabis nutrient deficiency.
Other causes of yellow and brown spots on leaves
Chlorosis and NPK deficiencies
Chlorosis in marijuana plants is the yellowing of leaves due to a lack of chlorophyll.
It is often related to cannabis NPK deficiencies (nitrogen, phosphorus, potassium) or micronutrient shortages.
If the leaves start to yellow from the tips or intermediate areas and then develop small brown spots, the fertilization program needs adjustment.
To prevent this, we recommend using fertilizers specifically formulated for cannabis and following a watering schedule appropriate for each growth phase.
In our online store, you will find growth and bloom fertilizers, boosters, and deficiency correctors.
Improper pH and overwatering
Even with a good fertilizer, if the pH is outside the ideal range, the plant cannot properly absorb nutrients.
This may cause symptoms similar to a cannabis nutrient deficiency, including leaf spots or burns.
Overwatering marijuana is also very common: roots become deprived of oxygen, leaves turn soft and droopy, then yellow, and eventually brown.
On the other hand, underwatering results in dry, brittle leaves.
- Use pH and EC meters to monitor the nutrient solution.
- Use pH- or pH+ products to keep water within the correct range (6.0–7.0 in soil, 5.5–6.5 in hydroponics).
- Choose an airy substrate and allow it to dry slightly between waterings.
Pests and fungi
Cannabis leaf pests (mites, thrips, aphids…) typically leave small white dots, bites, or discoloration that can evolve into brown cannabis leaves.
Fungal spots on marijuana commonly appear in humid, poorly ventilated environments.
To detect pests, examine the underside of the leaves with a magnifying glass: eggs, moving specks, or fine webs indicate their presence.
For fungi, look for irregular, moist, or powdery spots.
- Neem oil and potassium soap for organic pest control.
- Suitable fungicides (always follow manufacturer instructions).
- Fans and extractors to improve air circulation.
- Hygrometers to monitor humidity and temperature.
Light burn and excessive heat
Cannabis light burn occurs when the lamp is too close to the canopy or too intense.
Upper leaves may bleach, then turn yellow, and eventually develop dry brown “toasted” spots.
If you suspect this issue, raise the lamp, reduce power, or adjust the photoperiod depending on the lighting type (LED, HPS…).
A thermometer with a probe and a climate controller are excellent tools for preventing heat-related damage.
How to correctly diagnose damaged leaves
- Visual inspection: check where the spots appear and examine both sides of the leaves.
- Irrigation control: too much water = soft leaves; too little water = dry leaves.
- pH and EC measurement: ensure the plant can absorb nutrients properly.
- Nutritional adjustment: correct cannabis NPK deficiencies or calcium/magnesium shortages.
- Treat pests and fungi: apply the appropriate product when needed.
At growshopweb.com, we do not sell marijuana containing THC, but we offer all the materials needed for healthy home cultivation: fertilizers, CalMag supplements, pH/EC meters, pest control products, organic fungicides, and accessories to optimize your grow space.
Conclusion
Yellow or brown spots on cannabis leaves do not necessarily mean your cultivation is lost, but they are a warning sign.
By learning to identify whether the problem is due to chlorosis in marijuana plants, irrigation mistakes, pests on cannabis leaves, fungal marijuana spots, cannabis NPK deficiencies, or light burn on cannabis, you can act in time and save your harvest.
This blog is purely informational and aimed at home growers who want to improve their techniques.
In our online store, you will find everything you need to keep your plants healthy and prevent the appearance of brown cannabis leaves or yellow marijuana spots.