How to treat yellow cannabis leaves

These crops may experience some unexpected events for both expert growers and beginners. Regardless of if you’re growing your plants in coco coir, soil or hydroponics, there are multiple stains manifested on cannabis leaves. One of the most common problems that we may face while growing cannabis are the yellow stains on the leaves. Here you’ll find all the information to know their origin and how to prevent them from appearing

Why do cannabis leaves turn yellow?

To find out how to treat yellow leaves on our marijuana plants, we must know first the reasons that may cause them. Moreover, once the first signs of stress are noticed, Revive from Advanced Nutrients can be used. Some of them are:

PH levels

Soil pH is one of the most important factors affecting the health of your marijuana plants. An imbalanced pH can seriously hinder the plant’s ability to absorb essential nutrients, potentially leading to nutrient deficiencies and yellowing leaves in marijuana. It’s crucial to understand how pH impacts nutrient availability in the substrate.

Optimal pH range for growing marijuana

The ideal pH range for growing marijuana depends on the growing medium you’re using:

• In soil: The optimal pH is between 6.0 and 7.0. This range ensures that most nutrients are efficiently absorbed by the plant’s roots.
• In coco coir: The pH should be kept between 5.5 and 6.5. While coco is slightly more acidic than soil, this range allows plants to access nutrients without the risk of nutrient lockout.
• In hydroponics: The ideal pH falls between 5.5 and 6.2. Since hydroponic plants rely entirely on nutrient solutions, keeping the pH within this range is essential to prevent nutrient deficiencies and support healthy growth.

Effects of an Unbalanced pH

• Low pH (Acidic): When soil pH drops below 6.0, nutrients like calcium, magnesium, and phosphorus become less available to the plant. This can lead to deficiency symptoms such as yellowing of older leaves. If you detect overly acidic conditions, you can gradually raise the pH by adding agricultural lime or dolomite to the substrate.
• High pH (Alkaline): When pH rises above 7.0, nutrients such as iron, manganese, zinc, and copper become insoluble, often resulting in micronutrient deficiencies and interveinal yellowing—especially a classic sign of iron deficiency. To lower a high pH, you can add elemental sulfur to the substrate or use acidic fertilizers to rebalance the soil environment.

How to measure and adjust soil pH

Accurate pH measurement is key to maintaining a healthy growing environment. You can use a digital pH meter or pH test strips to check the soil’s pH level. If you’re using a digital meter, make sure to calibrate it regularly to ensure accurate readings.

When adjusting pH, it’s important to do so gradually, as sudden changes can stress your plants. Apply corrective products like lime or sulfur in small amounts, and check the pH every few days until you reach the desired level.

Temperature stress

Temperature stress, whether from excessive heat or extreme cold, can cause marijuana leaves to turn yellow.

• Excessive heat: High temperatures can stress the plant and reduce its ability to absorb nutrients effectively.
• Low temperatures: Cold conditions can slow plant growth and lead to nutrient deficiencies, which often show up as yellowing leaves.

Solution: Keep your plants in a stable environment with temperatures between 68–86°F (20–30°C), depending on the strain. If growing outdoors, provide shade during the hottest parts of the day to prevent overheating.

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Improper watering

Both overwatering and underwatering can cause marijuana leaves to turn yellow.

• Overwatering: When roots can’t get enough oxygen due to excessive watering, the plant becomes stressed and leaves start to yellow. Constantly waterlogged soil drowns the roots, leading to root rot. This prevents the plant from properly transporting nutrients, causing the leaves to yellow and wilt.
• Underwatering: On the other hand, if the plant doesn’t receive enough water, it won’t be able to perform photosynthesis efficiently. This leads to dehydration and yellowing leaves, ultimately affecting the plant’s overall health.

Solution: Make sure the growing medium has good drainage, and only water when the top few inches of soil feel dry. Adjust your watering frequency based on the climate conditions and the plant’s growth stage.

Fertilizer management

A lack of nutrients may produce nutritional deficiencies and interrupt the cannabis growth as this prevents the plants from performing their vital functions. Over fertilizing your plants may cause nutrients to be burnt and, consequently, leaf yellowing. Thus, it is important to remember that nitrogen, phosphorus and potassium (NPK) are essential nutrients for plants.

The most common nutrient problems are:

• A symptom of a lack of nitrogen that can be seen as it starts yellowing the edges of the leaves and then spreading this color all over them. However, if you see bright leaves during the growing stage, it may be due to over fertilization.

• The lack of potassium, the essential mineral to carry out photosynthesis and stoma function, causes your leaves to start turning yellow when there’s a deficiency of this compound. 

To avoid these problems, it is crucial to manage the nutrient levels, as well as knowing all the benefits that nutrients provide to every plant.

Nutrient deficiency

Plants need a variety of nutrients to stay healthy. A deficiency in any of them can show up as yellowing leaves:

• Nitrogen deficiency: Older leaves turn yellow as the plant redirects available nitrogen to the new growth.
• Iron deficiency: New leaves turn yellow, but the veins remain green (interveinal chlorosis).
• Magnesium deficiency: Yellow spots appear between the veins of the leaves.

Solution: Use a balanced fertilizer and make sure the substrate’s pH allows for proper nutrient absorption. For more details, check out our post on nutrient deficiencies and excesses in marijuana plants.

Pests and fungal diseases

Both pests and fungal infections can cause marijuana leaves to turn yellow. These issues often damage leaf cells by feeding on the plant’s sap or interfering with photosynthesis.

• Pests: Mites and other insects suck the sap from the leaves, leading to yellowing and overall weakening of the plant. A common culprit is the whitefly, which often causes chlorosis (yellow leaves). Check out our handy guide to the best insecticides for whiteflies.
• Fungal diseases: Conditions like powdery mildew interfere with photosynthesis and contribute to leaf discoloration.

Solution: Inspect your plants regularly and use treatments like neem oil or insecticidal soap to control pests. If you notice signs of fungal infection, apply natural fungicides to stop the spread and protect your crop.

Natural aging

As marijuana plants grow, older leaves may turn yellow and fall off. This is a normal part of the plant’s life cycle and isn’t a cause for concern.

Solution: Remove yellow leaves so the plant can focus its energy on new growth.

Inadequate substrate

A poor-quality substrate that lacks proper drainage or nutrients can harm your plants. Compacted soil prevents roots from breathing and absorbing nutrients, leading to yellowing leaves.

In this case, it’s best to use a high-quality substrate that is well-aerated and drains properly.

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Use of chemicals

Overusing fertilizers or pesticides can burn the roots and leaves, causing an unsightly case of yellowing in both indoor and outdoor marijuana plants. This issue is known as nutrient toxicity.

It’s strongly recommended to follow the manufacturer’s instructions carefully when using chemical products and avoid overapplication.

What to do if your marijuana plant’s leaves turn yellow

When your marijuana plant’s leaves start turning yellow, it’s important to stay calm and methodically identify the cause to apply the right solution.

As we’ve seen, chlorosis (leaf yellowing) can be triggered by a wide range of factors. To make an accurate diagnosis, you’ll need to thoroughly inspect the plant and its environment to pinpoint what might be going wrong. Follow these steps to identify the potential cause:

Step 1: Observe the yellowing pattern

Start by analyzing how and where the yellowing is happening. This can give you clues about the underlying issue:

• Lower (older) leaves turning yellow: Usually a sign of nitrogen deficiency or the natural aging process.
• Upper (newer) leaves turning yellow: Could point to a deficiency in iron, zinc, or calcium.
• General yellowing across the plant: May result from overwatering or underwatering, pH imbalance, or inadequate lighting.
• Yellow spots between leaf veins: Often indicates a magnesium deficiency.

If you suspect a specific deficiency, consider using a targeted supplement or a complete cannabis fertilizer to correct the issue.

Step 2: Check your watering practices

Watering issues are among the most common causes of yellow leaves. Here’s how to determine if it’s the problem:

• Feel the substrate by sticking your finger 1–1.5 inches (2–3 cm) into the soil. If it feels soaked, you’re likely overwatering. If it’s dry and dusty, the plant is underwatered.
• Check for proper drainage. Make sure your pot has drainage holes and that water isn’t pooling at the bottom.

Step 3: Check the pH of the substrate and water

An incorrect pH can prevent nutrient absorption, leading to yellow leaves.

• Test the substrate pH using a digital pH meter. It should be in the optimal range of 6.0 to 7.0 for cannabis.
  • If the pH is too high (alkaline), lower it using an acidifier like vinegar, citric acid, or a dedicated product such as pH- Boom.
• Test the pH of your irrigation water and make sure it’s also between 6.0 and 7.0.
  • If the pH is too low (acidic), raise it using baking soda or a product like pH+ Boom to adjust the acidity level.

Step 4: Inspect the plant for pests or diseases

Pests and diseases can also affect indoor plants, so it’s important to check them carefully and frequently.

• Inspect the leaves for signs of insects such as spider mites, whiteflies, or aphids.
• Check the substrate for the presence of larvae or fungal growth.
• Look for spots or deformities on the leaves, which may indicate a fungal or bacterial infection.

If you spot pests, use an organic insecticide like neem oil, or a chemical one if necessary. In case of fungus, apply a fungicide and improve air circulation in your grow space.

Step 5: Check environmental conditions

Poor environmental conditions can also cause yellow leaves. Make sure to evaluate the following factors:

• Temperature: Extreme heat or cold stresses the plant.
  Keep daytime temperatures between 68–82°F (20–28°C) and nighttime between 59–72°F (15–22°C).
• Humidity: Both too much and too little humidity can impact plant health. Maintain relative humidity at 40–60% during the vegetative stage, and 40–50% during flowering.
• Lighting: Too much or too little light can lead to yellowing.
  Ensure your plant gets the right amount: 18 hours of light during the vegetative phase, and 12 hours during flowering.

Here’s a helpful table summarizing the most common symptoms and causes of yellow leaves in indoor marijuana plants:

	Possible Cause	Recommended Solution
Yellow leaves with dry brown tips	Underwatering or low humidity	Increase watering frequency and use a humidifier if the environment is dry.
Yellow and soft leaves	Overwatering or root rot	Reduce watering and improve substrate drainage. If rot is present, prune affected roots.
Yellow leaves with green veins (chlorosis)	Iron or zinc deficiency	Apply iron chelates or micronutrient-rich fertilizers.
Lower leaves turning yellow and dropping early	Nitrogen deficiency	Use a fertilizer with a higher nitrogen (N) concentration.
Leaves with scattered yellow spots	Pest attack (mites, thrips, aphids)	Inspect and treat with potassium soap or neem oil.
Yellow leaves with curled edges	Temperature stress or drafts	Keep the plant within a range of 64–77°F (18–25°C) and avoid sudden changes.
Yellow leaves with brown spots	Excess sunlight or burns	Move the plant to a spot with indirect light or use a curtain to filter sunlight.
Yellow leaves with weak growth	Lack of light	Place the plant in a brighter area or use a grow LED light.
Yellow leaves with a sticky appearance	Honeydew from insects (aphids, mealybugs)	Wash the leaves with water and potassium soap, and manually remove the pests.

Trends in solutions and products to combat yellow leaves in marijuana plants

The marijuana cultivation market is constantly evolving, with new products and technologies emerging to help growers keep their plants healthy.

• Smart irrigation systems: Automated watering systems regulate the amount of water plants receive, preventing issues related to overwatering or underwatering.
• Biological nutrient supplements: Products like worm castings and biochar enhance soil quality and ensure plants get all the essential nutrients they need.
• Biological insecticides: The use of organic pest control solutions, such as neem oil, is becoming increasingly popular as growers look to avoid harsh chemicals and protect the ecosystem’s health.

How to prevent yellow leaves in marijuana plants

Keeping your marijuana plants healthy and free of yellow leaves is much easier when you follow proper preventive practices:

• Proper watering: Striking the right balance prevents both underwatering and overwatering—two of the main causes of yellowing. Use a soil moisture meter for better accuracy.
• Balanced nutrition: Too much or too little of certain nutrients can lead to yellow leaves and other problems. Use cannabis-specific fertilizers and adjust dosages according to the plant’s growth stage. (In this post, we explain how to choose the best fertilizer for indoor plants.)
• pH control: An incorrect pH level can block nutrient absorption. Regularly check the pH of both the substrate and irrigation water, and adjust it if needed.
• Correct lighting: Light is the engine of photosynthesis, but too much or too little can be harmful. The right balance is key to avoiding yellow leaves. Use proper grow lights (LED, HPS) and adjust their distance to the canopy.
• High-quality substrate: Poor-quality substrates can cause serious issues. Choose cannabis-specific growing mediums, like Light Mix Boom Nutrients, which are airy and nutrient-rich.
• Pest and disease prevention: Apply preventive treatments like neem meal or insecticidal soap, and maintain a clean grow area to prevent the spread of pests.
• Temperature and humidity control: Keep daytime temps between 68–82°F (20–28°C) and nighttime between 59–72°F (15–22°C). Use fans and extractors to ensure a stable, well-ventilated environment.
• Regular pruning: Pruning improves plant appearance, encourages healthy growth, and helps prevent disease. Remove yellow, dead, or diseased leaves using sterilized scissors.

Here’s a quick summary of all the preventive measures to keep your plants thriving.

	Specific Action
Proper watering	Only water when the substrate is dry.
Balanced nutrition	Follow the recommended fertilizer dosages.
pH control	Measure and adjust pH regularly.
Proper lighting	Provide the right amount of light.
High-quality substrate	Use cannabis-specific growing mediums.
Pest prevention	Inspect your plants regularly.
Temperature control	Maintain a stable and well-ventilated environment.
Regular pruning	Prune with clean tools and remove debris.
Stage-based adjustments	Adapt care according to the growth phase.

In conclusion, yellow leaves on indoor plants like marijuana are a clear sign that something isn’t right in your grow. Whether it’s due to overwatering, nutrient deficiencies, lighting issues, or pests, the key is to identify the problem early and take the appropriate steps to fix it—ensuring healthy growth and a successful harvest.

If you want to keep improving your cannabis cultivation skills and solve any issues that arise along the way, don’t miss our upcoming posts.

Yellowing leaves in marijuana are a common symptom that something’s off in your grow. But by pinpointing the cause and applying the right solutions, you can restore your plants’ health and ensure they grow strong and productive. Stay up to date with the latest trends and products to refine your growing techniques and get the most out of your crop.