8 Reasons Cannabis Leaves Turn Yellow
Cannabis can be a sensitive and challenging plant to grow. Many growers struggle with knowing how to keep a plant healthy. One of the most common signs a plant is in need of some extra love is when you see yellowing leaves. In addition to being a common problem, there are also many reasons why a plant may not be able to maintain a nice green color.
Yellowing leaves often occur when a plant is trying to tell you something needs attention or correcting in order to achieve medicinal-grade flower
It’s important to know that providing ideal environmental conditions will be key to achieving peak plant health and performance. It’s also good to know that a plant will not keep all of its leaves for its entire life. Some leaves will turn yellow and some leaves will need to be removed throughout the life of the plant. It’s completely normal. Yellowing leaves are also normal in many varieties of cannabis as they near the end of bloom.
Some common problems that cause leaves to yellow and need to be corrected in order to achieve medicinal-grade flower include:
Problem 1: Too Much Water
Giving a plant too much water is one of the most common mistakes growers make. It can quickly kill a cannabis plant. This is a plant that needs containers that drain well and a soil mixture that promotes drainage. Too much water can cause root rot and prevents a plant from being able to properly uptake nutrients. Putting a plant in the proper container will help dramatically decrease the likelihood that a plant will get overwatered.
Another important growing tip is to make sure you don’t water too often, only when the soil is in need of hydration. It’s helpful to pick up a pot each time you water it to learn the watering needs of each strain. Pick it up when it’s light and dry and after you water it. Water needs will be strain dependent. Many strains actually prefer less water than others. Crippy, Animal Cookies, and Forum Cookies, for example, are some strains that need less water. Gorilla Glue #4 and GMO are plants that prefer more water. The goal is to water before a plant wilts, but after the soil has dried up enough.
Problem 2: Not Enough Light
Cannabis plants love light! Make sure your plants receive at least 7-8 hours of direct light every day for the best results. It’s also important to properly train and maintain a plant to ensure the entire plant gets enough light exposure. Using stakes or a trellis net and lollipopping each plant will really help a plant get the light it needs. In addition to yellowing leaves, a plant can become stressed from not receiving enough light and can herm.
If you are growing indoors, make sure you have the right light fixture for your space as well as the correct number of lights, which will determine the number of plants you can successfully grow in a room. Many lights, like LEDs, have different settings as well. It’s important to figure out what setting your plants want. Sometimes when switching to a new light fixture, or introducing certain strains to a fixture, you want to start on a lower setting and then increase it as a plant acclimates to the intensity.
Problem 3: Not Enough Nutrients
Yellowing leaves may also be a sign that you aren’t providing your plants with enough nutrients. Nutritional content is found in both the soil and food source (liquid or granular). The pH and parts per million (PPM) of the soil and nutrients are also important when caring for cannabis plants. If a cannabis plant is lacking or receives too much of a certain nutrient, it can affect the availability of other nutrients, thus causing deficiencies and yellowing leaves.
Plants perform well when nutrients are mixed into the soil, which will slowly release over time as they break down from microbial life and water. Top dressing, teas, and bottled nutrients are quick release forms of nutrients and are available for a plant to use right away. By providing both slow and quick release nutrients, a plant will have a constant supply of nutrients, and if given in the correct amounts at the correct times, will allow a plant to maintain good health, lessening the likelihood of acquiring issues like yellowing leaves.
Problem 4: Overcrowded Plants
It’s not uncommon for growers to run out of gardening space, especially if they are growing indoors and have limited space to begin with. It’s important not to have too many plants in a space, or plant health and the health of your entire garden can suffer. Crowded conditions make it easy for pests and pathogens to settle and go unnoticed in addition to making it difficult for a gardener to properly inspect each plant.
Plants also need enough space to ensure proper light exposure and air circulation. When plants are too close together, tall ones shade the smaller ones, which can cause deficiencies, typically showing up as yellow leaves. Plants will compete for light, and if in the same container, will also compete for moisture and nutrients. Ideally plants would be placed at a distance of 2-4 feet apart, but if space is an issue, should be placed far enough away from each other that their leaves don’t touch.
Problem 5: Pest Pressure
If you grow cannabis, you will encounter pests from time to time, if not constantly. Pests love cannabis plants. Summer is the most challenging time of the year when it comes to pests as the warm weather attracts them and is a time when they mate and lay eggs.
It cannot be stated enough, if you notice the presence of pests, immediate action is needed to successfully control and eliminate them before an infestation occurs. In large numbers, pests can quickly lower plant health. Some pests, like aphids, lace bugs, and mites can cause leaves to quickly yellow; appearing pretty much anywhere on a plant.
Prevention is key when it comes to keeping genetics around for a long time, but if pests do show up, having the proper tools on hand will help make things easier. It’s always good to have a pump sprayer or atomizer in addition to organic sprays like Kangen 2.5 Acid Water and Grow Safe or Spinosad.
Problem 6: Plant Pathogens
Pathogens like Powdery Mildew can also cause leaves to change from green to yellow especially if it’s allowed to progress. To avoid an outbreak, again, prevention is recommended. Spray plants 2x a week to eliminate any spores from settling and taking over a plant and garden. Keep areas like the floor as dry as possible. It’s also important to have adequate air circulation in a garden, indoors or outdoors. Multiple fans will likely be needed. It’s a simple thing to incorporate, however, will dramatically lower the likelihood that a plant will suffer from PM or mold issues.
Problem 7: Spraying With Light
Part of caring for a cannabis plant involves spraying it with a foliar spray or pest and pathogen preventative/treatment sprays. If a plant is sprayed and then exposed to light, it will burn, causing its leaves to turn yellow and possibly have brown tips. Yellowing can occur the next day, or even several days after being exposed to a spray. It’s important to apply sprays after lights out indoors, or right before sunset if plants are outdoors. Because plants aren’t as affected by green light, you can use a green light to see in a grow room while you spray the plants and then turn it off when you’re done. A spray needs a solid 4+ hours to dry on a plant before light can touch it again.
Problem 8: The VPD Is Off
Cannabis is sensitive to temperatures that are too hot or too cold and shouldn’t be exposed to dramatic fluctuations between night and day. Humidity also plays a role in a plant’s ability to effectively transpire, or move water and nutrients throughout its leaves and branches. VPD will change slightly between a vegging and flowering plant, however, should be closely monitored to help a plant perform necessary functions, discourage pathogens, and maintain good health.
Make sure to not put plants outside if you live in an area that experiences freezing temperatures. It’s best to wait for summer months or when the temperature is above 60-65 degrees F. If the weather is not ideal, the plant will let you know with yellowing leaves.
Green Is The Goal
Plants will often first show signs of distress by exhibiting yellow leaves, so be sure to pay attention if you see them appear. Yellowing leaves don't always indicate a major issue, so be sure to inspect a plant to determine what might be causing its leaves to change color. The more time you spend in your garden, the more likely you'll catch things early on, and the faster you'll be able to learn the art of correctly reading a plant.
