Brown Spots on Weed Leaves

Brown spots on weed leaves are a common issue in the cannabis growing community. While they may not be attractive, they can wreak havoc on your crop if left unchecked.

This blog post will discuss the causes of brown spots on weed leaves and how to prevent or fix them. First of all, it’s important to understand what these spots are and why they occur.

Brown spots are typically caused by nutrient deficiencies in the soil, light stress from too much or too little light, pests and other environmental factors.

We’ll cover each of these potential causes in greater detail below and provide solutions for tackling them head-on.

There are several potential causes of brown spots on weed leaves. These include:

  1. Nutrient deficiency – If your plant is lacking in key nutrients, this can cause the leaves to turn brown. Common nutrient deficiencies that can cause this problem include nitrogen, phosphorus, and potassium.
  2. Light stress – Too much or too little light can both cause the leaves of your plant to turn brown. Make sure you are providing your plant with the right amount of light for its needs.
  3. Temperature stress – Extreme temperatures, either hot or cold, can also cause brown spots on weed leaves. Make sure you are maintaining a stable temperature range for your plants.
  4. Herbicide damage – If you have sprayed your plants with an herbicide that contains glyphosphate, this can cause the leaves to turn brown and eventually die. If this is the case, you will need to remove all affected leaves and stems and dispose of them properly.
  5. Pest infestation – Various pests can also cause brown spots on weed leaves. Common culprits include spider mites, aphids, and whiteflies. If you suspect that your plant has a pest problem, you will need to take steps to control the infestation immediately

Brown Spots on Marijuana Leaves: Causes and Solutions

There are a few different reasons why brown spots might appear on your weed leaves. If the spots are small and circular, they could be caused by spider mites.

These pests are very small, but they can do a lot of damage to your plants. If you think spider mites might be the problem, you can try treating your plants with an insecticide.

Another possible cause of brown spots is a fungal disease called powdery mildew. This disease is often caused by overwatering or humid conditions. To treat powdery mildew, you can use a fungicide.

If the brown spots on your weed leaves are large and irregularly shaped, they could be caused by herbicides. Herbicides can drift onto your plants from neighboring properties, so if you live in an area where there is a lot of agricultural activity, this could be the problem. The best solution is to try to avoid using herbicides on your own property, and to encourage your neighbors to do the same.

a graph showing herbicide application trend per million acres in 2001

Nutrient deficiencies

When it comes to cannabis plants, nutrient deficiencies are often to blame for brown spots on the leaves. This is because nutrients are essential for proper plant growth and health. When a plant is lacking in nutrients, its leaves will often turn brown or yellow as a result.

There are a number of different nutrient deficiencies that can cause brown spots on weed leaves. Some of the most common include:

Nitrogen Deficiency: This is one of the most common nutrient deficiencies in cannabis plants. Nitrogen is essential for healthy growth and development, and when it’s lacking, leaves will often turn yellow or brown.

A simple way to correct a nitrogen deficiency is by adding more nitrogen-rich fertilizer to the soil.

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Phosphorus Deficiency

Phosphorus is another key nutrient for healthy plant growth. It helps with root development and promotes flowering. When phosphorus is deficient, leaves may turn purple or red. Adding phosphate-rich fertilizer to the soil can help correct this deficiency.

Potassium Deficiency: Potassium is important for overall plant health and plays a role in water uptake and photosynthesis. Leaves may turn yellow or brown when potassium levels are low. Adding potassium-rich fertilizer to the soil can help alleviate this problem.

Marijuana with Phosphorus Deficiency
Marijuana with Phosphorus Deficiency

Magnesium Deficiency: Magnesium helps with chlorophyll production and plays a role in photosynthesis. When magnesium levels are low, leaves may turn yellow or brown around the edges. Applying magnesium sulfate (Epsom salt

Calcium deficiency

Calcium is a vital macronutrient for cannabis plant health, playing a role in cell wall strength and water uptake. A lack of calcium can lead to various problems in plants, such as brown spots on the leaves.

There are several possible causes of calcium deficiency in plants, including poor soil quality, incorrect watering, and inadequate nutrition. Luckily, there are also several solutions to fix the problem.

Marijuana with Calcium Deficiency
Marijuana with Calcium Deficiency

To start, you need to identify the cause of the calcium deficiency. Once you know the cause, you can implement the appropriate solution.

If the problem is due to poor soil quality, you need to improve the drainage and add more organic matter to the soil. If incorrect watering is to blame, make sure you’re watering deeply and evenly. And if inadequate nutrition is the issue, fertilize your plants with a calcium-rich fertilizer or simply add some limestone to your garden beds.

With a little effort, you can quickly correct a calcium deficiency in your plants and enjoy healthy, green foliage once again.

Nitrogen deficiency

Nitrogen is one of the three primary nutrients that plants need to thrive, and it plays a critical role in photosynthesis, the process by which plants convert sunlight into energy. Nitrogen deficiency is one of the most common problems that gardeners face, and it can manifest itself in a number of ways, including yellowing leaves, stunted growth, and brown spots on weed leaves.

Marijuana with Nitrogen Deficiency
Marijuana with Nitrogen Deficiency

While nitrogen is readily available in the atmosphere, it must be converted into a usable form by bacteria in the soil before plants can take it up.

This process is called nitrogen fixation, and it can be inhibited by a number of factors, including cold weather, drought, and compacted soils. If your plants are showing signs of nitrogen deficiency, there are a few things you can do to correct the problem.

The first step is to test your soil to see if it is deficient in nitrogen. You can do this yourself with a simple soil test kit, or you can send a sample of your soil to a professional testing lab. Once you know for sure that your soil is lacking in nitrogen, you can take steps to amend it.

Adding compost or manure to your garden beds is a good way to add organic matter and improve the ability of your soil to hold onto nitrogen. You can also apply commercial fertilizers that contain nitrogen.

Be sure to follow the instructions on the package carefully so that you don’t over-fertilize and damage your plants.

Potassium deficiency

Potassium is one of the three essential macronutrients that plants need for proper growth and development. It is involved in numerous plant processes, including photosynthesis, water uptake, and enzyme activity. Potassium deficiency is a common problem that can cause brown spots on weed leaves.

Marijuana with Potassium Deficiency
Marijuana with Potassium Deficiency

Symptoms of potassium deficiency include brown or yellow spots on leaves, stunted growth, and leaf tissue death. Potassium-deficient plants are often more susceptible to disease and pests.

There are several ways to correct potassium deficiency. One is to add potassium-rich fertilizer to the soil. Another is to spray the leaves of the affected plant with a potassium solution.

If you suspect that your plant has a potassium deficiency, it is important to take action immediately. Addressing the problem early will help ensure that your plant remains healthy and vigorous.

Boron deficiency

Boron is an essential micronutrient for weed plant growth and development. It plays a role in cell division, cell wall formation, and photosynthesis. Boron is also involved in nitrogen fixation, uptake of phosphorus, and the synthesis of certain enzymes.

Boron deficiency can cause a number of problems in cannabis plants, including stunted growth, reduced flowering, and brown spots on leaves.

Brown spots on leaves are caused by boron deficiency can be distinguished from other types of leaf spot diseases by their irregular shape and light brown color. Boron-deficient plants may also have yellow or chlorotic leaves.

Marijuana with Boron Deficiency
Marijuana with Boron Deficiency

Boron deficiency is often caused by low levels of boron in the soil. This can be due to leaching from sandy soils or to the use of water with a high pH (which decreases the availability of boron). Boron can also be lost from the soil through crop removal. Some crops, such as potatoes and alfalfa, are particularly prone to boron deficiency because they take up large amounts of the element from the soil.

To correct boron deficiency, add 2-4 pounds of actual borate (not elemental boron) per acre to the soil. Apply this material in 20-40 gallons of water per acre using ground equipment only when conditions are favorable for plant growth (i.e., when soils are not too wet or cold). If conditions are not favorable for applying amendments to

Low pH levels

Weed leaves usually have a pH level between 6.0 and 7.0.

However, if the pH level drops below 6.0, the leaves will start to turn brown. This is because the plant can’t absorb nutrients from the soil properly when the pH is too low.

Low pH levels in marijuana leaf
Low pH levels in marijuana leaf

There are a few things that can cause low pH levels in the soil, such as using too much fertilizer or not enough aeration. If you think that your soil might be too acidic, you can test it with a pH meter or strips.

If the pH level is indeed low, there are a few things you can do to raise it back up.

You can add limestone or other calcium-rich materials to the soil to help neutralize it. You can also try watering your cannabis plants with diluted vinegar, which will help raise the pH over time.

Light burn

If you notice brown spots on your weed leaves, it’s likely due to light burn. Light burn occurs when your plant is exposed to too much light, which can cause the leaves to turn brown and dry out.

cannabis light burn on cannabis leaf
cannabis light burn on cannabis leaf

The best way to prevent light burn is to give your plant plenty of ventilation and make sure it’s not getting too much direct sunlight. If you think your plant is suffering from light burn, try moving it to a shadier spot and see if the problem improves.

Problems with heat and poor air circulation

If you notice brown spots on your weed leaves, it could be a sign of a problem with the heat or air circulation in your grow room. If the temperature is too hot, the leaves will start to turn brown and dry out. If the humidity is too high, the leaves will also start to turn brown and rot.

To fix these problems, you need to increase the ventilation in your grow room and make sure that the temperature and humidity are well-regulated. You can do this by adding more fans or opening up windows. If you live in a humid climate, you might need to invest in a dehumidifier to keep the air in your grow room dry.

Watering conditions: Overwatering or underwatering

If your weed plants have brown spots on their leaves, it could be a sign that they are either overwatered or underwater.

Overwatering can cause the leaves to turn brown and drop off, while under-watering can cause them to wilt and eventually die. If you’re not sure which it is, try letting the soil dry out for a day or two before watering again. If the brown spots return, then you know it’s an issue with too much water.

Bugs or pests

Weed leaves with brown spots can be caused by a variety of bugs or pests. Aphids, mites, and whiteflies are all common culprits. These pests can cause damage to the leaves of your weed plants, which can lead to brown spots.

There are a few things you can do to get rid of these pests. You can use insecticidal soap or neem oil to kill them. You can also try using ladybugs or lacewings, which are natural predators of these pests.

If you have brown spots on your weed leaves, it’s important to identify the cause so that you can find the best solution.

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How to prevent brown spots on weed leaves: Basic tips

As any gardener knows, brown spots on leaves are unsightly and can indicate a serious problem. Here are some basic tips on how to prevent brown spots on weed leaves:

  • Water early in the day so that the leaves have time to dry before nightfall.
  • Avoid overhead watering, which can promote fungal growth and lead to leaf spot problems.
  • Mulch around plants to help retain moisture and prevent soil splashing onto leaves.
  • Inspect plants regularly for signs of pests or disease, and take action immediately if problems are found.

By following these simple tips, you can help prevent brown spots on your weed leaves and keep your garden looking its best.


Brown spots on weed leaves can be caused by a variety of factors, from too much nitrogen to the wrong light cycle.

It is important to identify the cause before taking any corrective action in order to ensure that you are able to successfully get rid of the problem and restore your plants back to optimal health.

Thankfully, there are plenty of solutions available depending on what is causing the brown spots, so take some time to do your research and find out which one best suits your need!

Frequently asked questions about brown spots on marijuana leaves

What do brown spots on pot leaves mean?

Brown spots on weed leaves can be unsightly and may even reduce the quality of your crop. But what exactly are they? Brown spots on weed leaves are typically caused by one of three things: nutrient deficiency, pests, or disease.

Nutrient deficiency is by far the most common cause of brown spots on weed leaves. When a plant doesn’t have enough of certain nutrients, it will start to show signs of stress. This includes yellowing or pale leaves, as well as brown spotting. The most common nutrient deficiencies that cause brown spotting are nitrogen and magnesium deficiencies.

Pests can also cause brown spots on weed leaves. Common culprits include spider mites, aphids, and thrips. These pests suck the sap out of plants, causing them to become stressed and weak. This can lead to all sorts of problems, including brown spotting.

Disease is another possible cause of brown spotting on weed leaves. The most common diseases that affect cannabis plants are powdery mildew and botrytis (gray mold). Both of these diseases can cause the formation of Brown Spots On Weed Leaves.

Are brown spots harmful to cannabis plant’s leaves?

No, brown spots are not harmful to leaves and are actually quite common. There are a few different reasons why your weed leaves may have brown spots, but the most likely cause is simply due to age or stress. If your plant is healthy and receiving enough light, water, and nutrients, then the brown spots should not be a cause for concern. However, if the spots are accompanied by other signs of distress (such as wilting or yellowing leaves), then it could be indication of a more serious problem.

Does infection cause brown spots?

There are many potential causes of brown spots on weed leaves, and it can be difficult to determine the exact cause without further investigation. However, one potential cause of brown spots is infection from a fungi or bacteria. These infections can occur when leaves are wounded, allowing fungi or bacteria to enter the plant and causing the leaves to turn brown. In some cases, these infections can be controlled with fungicides or bactericides. However, it is important to properly identify the cause of the infection before treating, as some treatments may do more harm than good.

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Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

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