Why Are My Cannabis Leaves Turning Yellow? 9 Common Causes

Seeing your cannabis leaves turn yellow can feel like a panic moment - but don’t grab the scissors just yet. Yellowing leaves, or chlorosis, is your plant’s way of waving a big leafy flag that something’s off. The good news? Most yellowing can be reversed if caught early. Let’s break down the nine most common causes and how to handle each one like a pro grower.

1. Overwatering

🚩 What to Look For:

• Droopy leaves with a yellow tint
• Soil that’s consistently wet or soggy
• Slow growth

🛠 How to Fix It:

Let the soil dry out completely before watering again. Then adopt a "lift the pot" method: only water when the container feels light. Improve drainage with fabric pots or by mixing in perlite or coco coir.

2. Underwatering

🚩 What to Look For:

• Crispy, dry yellow leaves
• Soil pulling away from the sides of the pot
• Drooping leaves with upward curling edges

🛠 How to Fix It:

Give your plant a slow, deep watering. Stick to a consistent schedule and keep an eye on the top inch of soil - if it’s dry, it’s time to water.

3. Nitrogen Deficiency

🚩 What to Look For:

• Lower leaves turning pale yellow, then falling off
• New growth stays green, but older leaves yellow fast
• Slower overall growth

🛠 How to Fix It:

Use a nitrogen-rich fertilizer. For organic options, try worm castings, compost tea, or a fish emulsion feed. Make sure your pH is dialed in (around 6.0–6.5 in soil) so nutrients are actually absorbed.

4. pH Imbalance

🚩 What to Look For:

• Random yellowing, even when feeding correctly
• Nutrient lockout symptoms like brown spots or twisted growth
• Stunted plants despite good lighting and airflow

🛠 How to Fix It:

Test your water and soil pH. Cannabis prefers 6.0–6.5 in soil and 5.8–6.2 in hydroponics. Adjust with pH Up or Down solutions as needed, and flush the plant if it’s severely out of range.

5. Root Bound Plants

🚩 What to Look For:

• Yellowing despite regular feeding and watering
• Roots poking out of drainage holes
• Slowed or stunted growth

🛠 How to Fix It:

If you're growing in a pot that’s too small, it's time to transplant. Gently move the plant into a container that's 1–2 sizes bigger. Add fresh soil and water lightly to help it settle.

6. Light Burn

🚩 What to Look For:

• Yellowing or bleaching on upper leaves
• Leaf tips curling upwards or becoming brittle
• Symptoms only on leaves closest to the light

🛠 How to Fix It:

Raise your grow lights or dial back the intensity. Use the hand test: if your hand feels hot after holding it under the light for 30 seconds, your plant is too close.

7. Magnesium Deficiency

🚩 What to Look For:

• Yellowing between the veins of older leaves
• Red or purple stems
• Slow bud development

🛠 How to Fix It:

Add a cal-mag supplement or Epsom salts (1 tsp per gallon of water). Foliar feeding can also provide a fast magnesium boost.

8. Pests

🚩 What to Look For:

• Tiny white or yellow spots before overall yellowing
• Webbing, holes, or sticky residue
• Small bugs under the leaves (use a magnifying glass)

🛠 How to Fix It:

Inspect plants regularly. Use neem oil, insecticidal soap, or introduce beneficial predators like ladybugs. If infestation is severe, isolate the plant and treat aggressively.

9. Natural Leaf Aging

🚩 What to Look For:

Lower fan leaves turning yellow near the end of flowering
No other signs of stress
Plant otherwise healthy

🛠 How to Fix It:

No need to panic - this is normal! Your plant is redirecting energy to the buds. Simply pluck off the yellowing leaves to improve airflow and light exposure.

Yellow leaves aren’t the end of your grow - they’re the start of a diagnosis. Once you pinpoint the issue, your plant can bounce back fast. Whether it’s watering, pH, lighting, or pests, each yellow leaf is a clue. Pay attention, adjust accordingly, and you’ll be back to green in no time.

We’re not just another cannabis blog - we’re real growers who’ve made the mistakes, tested the methods, and tracked the results. HomeGrow Helpline is dedicated to breaking down complex grow topics into easy, honest, and actionable advice.