When you’re growing any plant, you take pride in it. You’ve grown it from seed, watched it sprout, and are trying to help it grow into a healthy, mature plant. So when you start seeing issues with the plant, you tend to get concerned. 

When you’re growing cannabis, one of the most common problems you may see is yellowing leaves. After all of the work you’ve put in growing your plant, this is the last thing you want to see. Don’t worry too much, though. Yellowing leaves are fairly common. 

Even if you’re following a comprehensive growing guide, you might run into your cannabis plant’s leaves turning yellow. If that’s the case, you’ve come to the right place. There are a number of different causes for yellowing cannabis leaves. In this article we’re going to cover the most common reasons behind yellow leaves, and how to get your plant back on the right track. Keep reading to learn everything you need to know about yellow cannabis leaves.

Common Causes of Yellow Marijuana Leaves

The thing that’s so shocking about seeing yellow leaves is what it signifies. Most of the time, people relate yellow leaves to the changing of seasons, when trees shed all of their foliage. This scares most people, since trees seem to die when the seasons change. If that happens to trees, it can’t be good for a smaller plant, right?

yellow leave scaled

You’d be right, there. Cannabis isn’t a perennial plant. It’s annual, meaning that when it dies off, it doesn’t regrow. If it starts dying before it’s harvestable, then you’re running the risk of being unable to harvest any of the plant’s desirable parts. Yellow leaves are the sign of an unhealthy annual plant, cannabis included. If it’s too early in the year for your cannabis to begin dying, then there may be a health issue you’re unaware of. Here are some of the most common reasons that cannabis plants will have yellowing leaves, and how to fix the issue.

Underwatering and Overwatering

Watering any plant is essential to its health. However, with cannabis, watering seems to be a balancing act. It’s easy for any new grower to underwater or overwater their plants. Yellowing leaves can be a sign that a cannabis plant is receiving too much or too little water. It’s important to understand the water needs of your plant, as it’s going to rely on water for growth over time.

Underwatering Cannabis Plants

When you’re underwatering your cannabis plant, the leaves begin to turn yellow due to a loss of nutrients. Plants are naturally green due to the chlorophyll that they produce. When you deprive your plants of water, the production of chlorophyll ceases, as the plant is doing everything it can to survive. It focuses its energy on keeping roots and stems alive since these are essential to staying alive. 

When your cannabis is underwatered, yellow leaves are one of a few warning signs. Others include drooping leaves and leaves that have thin, crisp tips.

How does underwatering happen, though? It can be the result of a number of different things. Sometimes, the substrate you’re growing your cannabis in doesn’t retain water well, or the watering schedule isn’t consistent enough. Thankfully, underwatering is one of the easiest problems to fix for your cannabis plant.

To fix yellow leaves due to underwatering, repot your cannabis plants in a substrate that retains moisture better. Additionally, be sure to schedule watering on a consistent basis. If your schedule doesn’t permit watering on a regular basis, consider getting a drip irrigation system, or a timed watering system.

Overwatering Cannabis Plants

Overwatering is a common problem for new cannabis growers. The perception is that more water will cause cannabis to grow more, so we want to give them as much water as we can. However, this isn’t always a good thing. Too much water results in yellowing leaves due to suffocation. Roots can’t get the oxygen they need to keep the plant’s vigor and resilience up. The result is cellular death in the leaves themselves.

When your cannabis is overwatered, you may notice heavy leaves that droop in addition to their color turning yellow. Your soil may also look like it’s underwater at all times.

overwatered plant scaled

For the most part, overwatering happens because we’re overzealous while growing our cannabis. If you combine that with feeding at night, pots that are too small, and low temperatures, overwatering is bound to happen.

Correcting overwatering is easy. First, if you suspect that you’ve overwatered your plants, let their potting medium dry entirely. This might take a few days. Then, create a better watering schedule for your plants. Only water when the first two inches of potting soil is dry. Make sure that the soil isn’t too packed, too, because a packed soil leads to higher water retention, increasing the chances of overwatering.

Over Fertilization and Under Fertilization

Like watering, fertilizer is an essential part of growing a healthy cannabis plant. Also like watering, fertilizing cannabis plants is a balancing act. It takes practice to learn how much fertilizer is appropriate to use, and how to tell when your cannabis plants aren’t getting the right amount of fertilizer.

With over-fertilization, leaves turn yellow due to what’s known as a nutrient burn. When they’re given their nutrients in excess, they begin to build up. As they build up. The plant has nowhere to put them. As the nutrients dissipate, they actually cause your plant’s leaves to burn and turn yellow. Before this, though, the leaves may seem more abundantly green. Dark, shiny green leaves occur during overfeeding before the yellowing from nutrient burn occurs. Leaves end up being vibrant yellow, and almost crunchy in some cases.

Under fertilization leads to its own set of issues. Rather than being afflicted by a nutrient burn, leaves are harmed by nutrient deficiencies. First, the edges of the leaves will begin to yellow. The yellowing will then continue onwards, reaching the center of the leaves. At a certain point, the leaves collapse, causing leaves to droop. They have a soft feel and are somewhat limp.

Over and under fertilization are easy issues to combat. For over fertilization, flush the plant’s soil with clean, pure water. Do this for the next few feedings. Then, resume feeding as it is instructed according to the product that you’re using. For under fertilization, up your feeding regimen until the yellowing, limp leaves appear to be healthier. Be careful not to over fertilize, though.

over fertilizing marijuanna plants

Nutrients and pH Lockout

When you grow cannabis, one of the most important and often overlooked aspects of growing is pH. The pH scale measures how acidic or basic something is. The scale ranges from 1 to 14. The lower end of the spectrum is acidic, while the higher end is basic. A completely neutral substance has a pH of 7. This is nearly impossible to achieve, so pH ranges are a bit more common to see when you’re delving into growing. 

When growing cannabis, the ideal pH medium it’s being grown in is 6.0 to 7.0. This is considered to be fairly neutral. Many substrates are hard to grow cannabis in for this reason. A pH that’s lower than this is common, with some growing mediums like coco being susceptible to ranges lower than 6.0. Generally, while 6.0 to 7.0 is ideal, 5.5 to 6.5 is considered acceptable pH for growing cannabis.

What happens when the pH level is off, though? Your plant experiences what is known as pH lockout. This is a condition where the plant cannot absorb the nutrients it’s being fed, thanks to the incorrect pH levels. This causes the plant to stop going through ideal growth, causing leaves to yellow. Often, yellowing leaves are the first sign of nutrient imbalances and pH lockout.

To fix pH lockout, there are tools that can be purchased to help monitor pH levels. These tools are called pH pens, and they give quick readings of the pH of the substances they’re put into. If you find that your pH is off, flush your plant’s substrate with pure water, like you would with over fertilizing. Then, invest in a pH-perfect fertilizer to help with pH issues. If all else fails, begin to provide the necessary micronutrients that your plant may be missing, after reading the fertilizer packaging that they’re missing, of course.

Light Deficiencies and Light Burns

Unless you’re growing your cannabis outdoors, a lighting solution is a big part of your growing setup. With artificial lighting, there are a number of challenges. In addition to having the right amount of light per day, you also have to have your lights at specific distances and have reflectors for when light is hard to come by in certain parts of your growing space.

With lighting, you have two sets of issues that cause yellowing leaves. The first of them is a light deficiency. Light deficiencies aren’t the most obvious issue, especially when you’re working with plants that are close to full maturation. When a cannabis plant isn’t getting enough light, yellowing leaves start at the bottom of the plant. This is the area in which light doesn’t make it. Shade from the other leaves at the top of the canopy can be an issue. The distance between the light and those leaves may be an issue as well since artificial light isn’t always going to be as effective as natural lighting in its delivery of nutrients.

light on marijuana plant scaled

The next issue to be concerned about has to do with too much light. When cannabis plants are given too much light or light that’s too intense, light burns are a result. This problem is much more noticeable than a light deficiency. The noticeable parts of the plants, the buds and the leaves at the top, will start to yellow. From time to time, the light will be so intense that leaves and buds will brown, becoming very burnt. This is rarer than yellowing, but it is still an issue to be aware of.

Lighting is the hardest part of building an efficient growing setup. It’s crucial to follow the manufacturer’s specifications when it comes to the distance between the light fixture and your plants. Correcting this may solve your light deficiencies and light burns. In the case that light deficiencies are still occurring at the bottom of larger plants, reflectors can be purchased. Consider looking into full setup specs for growing under artificial light conditions, as well.

Other Causes of Yellow Pot Leaves

While the four areas above are major areas of concern, there are other issues to be aware of, as well. These problems are less common than the ones listed above, but they still happen from time to time, causing your leaves to turn yellow. If your cannabis plants aren’t experiencing any of the issues listed above, you may find your problem listed below.

Plagues and Pests

If you’ve done any gardening whatsoever, you know that disease and pests are major issues for most plants. For tomatoes, you’ve got the massive hornworms. For squash, you have to worry about aphids and mites. Cannabis isn’t only desired by people, it’s got its own set of pests to worry about, too. While many of these pests only affect outdoor growers, they may find their way indoors, as well. Aphids, scale, and caterpillars are common.

Moving on from pests, you also have to be concerned about plant diseases that may affect your cannabis plants. Leaf spots, mildew, blight, wilt, and canker are all potential diseases that may affect your cannabis plants. These can be the result of floating spores or other plants that may be infected, passing them along through the roots. All of them pose a serious threat to your entire crop once they’ve started.

Any and all of these issues compromise the health of your cannabis plants. As the plants try to repair damaged systems, they divert their energy from growing to healing. This causes the leaves to turn yellow, as chlorophyll production is reduced.

If you’re experiencing problems with pests, there are a number of remedies available on the market. Having neem oil on hand is an excellent way to deal with any pests on the leaves of your plants. Additionally, companion planting can help, too. Companion plants can be plants that naturally drive pests away. To prevent diseases, mycorrhizal fungi can be added to your soil to defend against fungal diseases and other ailments. If you find that you have plants that are dying rapidly, they need to be removed from the population of other plants to prevent disease from spreading. Losing one plant is better than losing all of them.

Temperature Issues

Temperature issues have to do with both highs and lows. Occasionally, temperatures will rise or fall in an uncontrollable manner. This has an effect on your cannabis plants, and yellow leaves can be the result of the thermometer tipping in either direction.

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Cold Temperatures

When temperatures start to fall, the leaves of most plants change. Cannabis is no exception. As temperatures dip to 10°C or 50°F, the leaves of most strains of cannabis will turn yellow. Some will take on other colors, like blues and purples. Some strains actually get their names from these color changes. However, this change isn’t very desirable early on in a grow. If you planted too early in the year, your plants may see cold snaps that can kill their leaves early on.

If you’re growing indoors, increasing the temperature is an easy way to avoid yellowing as a result of lower temperatures. If you’re growing outside, plants may need to be brought in for colder overnight temperatures. If this isn’t possible, a DIY greenhouse or plant covering can prevent the pain of losing leaves due to cold snaps.

Hot Temperatures

Similar to cold snaps, heat waves and high temperatures will create yellow leaves, as well. The reason behind leaves turning yellow in the heat is mostly due to dry conditions. When temperatures rise, water evaporates too rapidly for the plant to absorb. This starts to occur at temperatures of 28°C or 82°F. Temperatures this high also prevent the plant from being able to photosynthesize correctly. This yellow leaves and causes buds to dry out.

When growing indoors, both air conditioning and adequate air movement are necessary. Without one, the process breaks down, resulting in dried out plants that are entirely yellow. If you’re growing outdoors, the best you can do is shade the plants and hope that the heat passes quickly.

Leaf Disease

While we already covered plagues and pests, there is a condition that’s deserving of its own section. Leaf septoria, more commonly known as leaf disease, is a fungal disease/infection that turns cannabis leaves yellow. It doesn’t just affect cannabis, though. It can be seen in plants like tomatoes and parsley as well.

The disease doesn’t start with yellowed leaves. Instead, the leaves of your cannabis plant will develop small black spots. These spots spread quickly from leaf to leaf, and soon your plant is entirely covered in them. Quickly, the spots turn brown, and the leaves begin to yellow and wilt. It’s a process that happens fairly rapidly, and entire plants will be covered in spotted or yellowing leaves.

Leaf Disease canabis

This pathogen starts to affect plants during the early flowering phase. If the fungus is allowed to spread, it destroys the foliage of entire plants, which causes growth issues. Without leaves, cannabis plants cannot create energy, leading to stunted plants and lackluster harvests.

While leaf disease can become rampant, it’s easy to get under control if noticed early. Any infected leaves need to be pruned from your cannabis plants. Then, any plants that were affected by the septoria need to be coated in neem oil. This helps destroy smaller patches of the disease that may have gone unnoticed. To prevent the leaf septoria from returning, increase air circulation in your growing space. For a greenhouse or a grow room, this can be done with fans. Outdoor growing may take more tweaking. Additionally, cleaning up the bases of plants and removing leaf litter prevents leaf disease from returning, as well.

Root Rot

Root rot is largely a product of overwatering your plants. When you overwater your plants, you give microbial pathogens the ability to grow in the plant’s soil. When this happens, they attack and feed on the roots of the plants, inhibiting the ability to absorb nutrients from fertilizers. When plants cannot get the nutrients they need, leaves begin to wilt and yellow. If the conditions that lead to root rot exist for too long, the roots actually begin to rot away, killing the plant slowly.

Once root rot has started, there are a few ways to fix it. First, mycorrhizal fungi can be introduced to the soil to help fight the detrimental microbes. Following this, you’ll need to take a look at your watering schedule. Root rot is likely happening due to overwatering. Allow the soil to dry out, and begin a more conservative watering schedule. If the root rot is severe, transplant the cannabis plant into fresh substrate. This helps remove any residual microbes contributing to the rot.

When Are Yellow Leaves Okay?

While you want to avoid yellow leaves, for the most part, they aren’t always a bad thing. Yellow leaves are a natural part of the growing cycle. Like any other living thing, cannabis plants have a life expectancy. At maturation, many of the older, original fan leaves are going to yellow and fall off of the plant. This is because the plant’s energy is being diverted to the flowering phase. To produce large buds, the plant stops growing its leaves and starts growing its flowers.

Additionally, leaves are going to turn yellow when you change parts of the growing process. It’s part of the plant adjusting to its new conditions and is entirely natural. You should only really worry when yellowing continues to happen, or when it happens before maturation is reached.

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