Yellowing Leaves?
Common Causes and Solutions for Cannabis Growers
As a cannabis grower, one of the most common issues you may encounter is yellowing leaves. Yellowing leaves can be a sign of various problems, ranging from nutrient deficiencies to watering issues. In this quick guide, we’ll briefly discuss the main causes of yellowing leaves that will help you diagnose and solve the problem.
Most Common Causes:
1. Nutrient Imbalances:
One of the most common causes of yellowing leaves is nutrient imbalances or deficiencies. To learn more about identifying and correcting nutrient issues, check out our in-depth article on Soil, Nutrients, and Deficiencies Here
2. Improper Watering:
Both overwatering and underwatering can lead to yellowing leaves. To ensure you’re watering your cannabis plants correctly, read our comprehensive guide on Watering Cannabis Plants Here
3. Incorrect Pot Size:
Plants in pots that are too small may show signs of nutrient deficiencies, yellowing leaves, and stunted growth due to limited soil volume, root lock and nutrient availability. Plants in oversized pots may suffer from overwatering and root rot, leading to yellowing leaves. Choose an appropriate pot size for your cannabis plant’s current growth stage and size. Read more Here
4. Pests:
Pests like fungus gnats who feed on your roots or thrips and mites that suck out the nutrients can lead to yellowing leaves so make sure to checkout our comprehensive guide on cannabis pests and remedies Here
Know Your Terminology
Types of Yellowing Leaves and Their Causes
1. Nitrogen Deficiency:
This is one of the most common reasons for yellow leaves and can start to appear early on. Older and lower leaves turn pale green or yellow. This starts from the bottom of the plant on the tips of the leaves and moves up and inwards. The leaves may also drop or die prematurely.
Solution: Increase nitrogen levels in your nutrient watering solution. Top dress your soil with organic nitrogen sources such as worm castings,blood meal or bat guano.
2. Phosphorus Deficiency:
This is a rarer problem by comparison and more common in flowering plants. It can be identified with yellow and brown spots on older growth. The leaf will start to die and change in colour first either by turning yellow or brown all along the leaf edges.
Solution: Increase the phosphorus levels in your nutrient or top dress your soil with organic phosphorus sources such as rock phosphate or bone meal
3. Potassium Deficiency:
This deficiency is most commonly associated with the flowering phase. The lower leaves start turning a yellow or brown unevenly around the edges while the center of the leaf remains healthy green. Older leaves develop yellow or brown spots along the margins, which may progress and start to curl or twist from all sides.
Solution: Increase potassium levels in your nutrient solution or make a banana peel compost tea.
4. Magnesium Deficiency:
With this deficiency the older leaves and old growth develop interveinal chlorosis (yellowing around the leaf veins), while the veins themselves remain green. This is usually easy to spot and to fix.
Solution: Supplement with magnesium, such as Epsom salts (1 teaspoon for every 2 liters of water), or use a cal-mag supplement.
5. Calcium Deficiency::
Calcium and magnesium deficiencies normally go side by side but in this case the young leaves and growing tips exhibit distorted growth with curled or cupped leaves, and brown or yellow blotches coupled with stunted growth.
Solution: Use a calcium supplement, such as cal-mag, and maintain a proper pH range for calcium availability.
6. Iron Deficiency:
As opposed to a magnesium deficiency, the younger leaves and new growth turn pale or yellow this time, while the veins still remain green.
Solution: Lower the pH of your growing medium or nutrient solution. Iron becomes less available at higher pH levels and should generally be present.
7. Sulfur Deficiency:
Younger leaves turn pale yellow or yellow-green, similar to nitrogen deficiency but affecting new growth first.
Solution: Ensure your nutrient solution contains adequate sulfur by adding some epson salts and maintain a proper pH range.
8. Zinc Deficiency:
Younger leaves exhibit interveinal chlorosis, similar to iron deficiency, but with a more pronounced yellowing between the veins. The leaf margins may also appear distorted or wrinkled.
Solution: Ensure your nutrient solution contains adequate zinc and maintain a proper pH range, as zinc becomes less available at higher pH levels. Foliar feeding with a zinc supplement can also be effective.
9. Manganese Deficiency:
Younger leaves develop interveinal chlorosis, similar to magnesium deficiency, but with a more mottled appearance. Brown, necrotic spots may also appear.
Solution: Lower the pH of your growing medium or nutrient solution, as manganese becomes less available at higher pH levels. Foliar feeding with a manganese supplement can also be effective.
10. Overwatering:
This is probably the most common reason for yellowing leaves. The leaves on a water soaked plant will turn pale yellow or yellow-green, and will feel soft and limp. If the soil remains wet and the pot stays heavy for extended periods your plant may be water locked and is slowly drowning. Overwatering is far more difficult to fix and the damage can be felt long term. Always water on a side of caution. Read more about proper watering techniques Here
Solution: Reduce watering frequency and ensure proper drainage.
11. Underwatering:
Although underwatering is generally easier to fix and recover from, regularly under watering your plant can also lead to yellow leaves and some serious problems. The stressed leaves will turn yellow and become crispy or brittle. They will not recover. This could leave your plant seriously defoliated even if you manage to save it. If the soil feels dry to the touch in the first 2-3 cm of the top soil and the pot is considerably lighter should water. Aim for a schedule of around every 3 -4 days or more frequent as the plant matures.
Solution: Increase watering frequency and water slowly to ensure the soil gets evenly moist.
Conclusion:
Yellowing leaves can be a frustrating problem for cannabis growers, but by understanding the common causes and solutions, you can quickly address the issue and get your plants back on track. If you’re unsure about the specific problem your plants are facing, refer to our detailed articles on nutrient deficiencies and watering for more information.
Remember, the key to healthy cannabis plants is providing the right balance of nutrients, water, and growing conditions. By staying attentive to your plants’ needs and addressing issues promptly, you’ll be well on your way to a successful harvest.
Sub Topics
Featured Products
Featured Guides
Sign up to our Promotion List
