Why Are My Cannabis Leaves Turning Yellow in July? Common Mid-Season Fixes

It's mid-summer, your cannabis plants are stretching tall, the buds are on the way… and then suddenly - you notice yellow leaves. Panic sets in. Did you overwater? Is it bugs? Is your whole harvest doomed? Don’t worry just yet - yellowing leaves in July is common, and in most cases, fixable. Let’s walk through the most likely causes and how to get your grow back on track before flowering kicks in.

1. It Might Just Be Natural Aging (But Check Where It’s Happening)

Before you break out the pH meter or neem oil, take a breath. If only the lowest, oldest fan leaves are yellowing, and the rest of the plant looks healthy, this could just be part of the plant’s life cycle. Cannabis sheds its lower leaves as it matures.

Quick fix:

Remove the yellowing leaves with clean snips to prevent mold and improve airflow. No need to panic unless the yellowing spreads upward.

2. Overwatering (Yes, Even in the Heat)

It's hot out. You want to baby your plants. But watering too often - even in July - can suffocate roots, causing yellowing, droopy leaves. Many growers mistake this for underwatering and make it worse.

What to check:

• Soil stays wet for more than 2 days
• Leaves are soft, limp, and yellow
• Roots smell swampy (if you’re in containers)

Quick fix:

Let the soil dry out before watering again. Lift pots to feel weight, and water only when the top inch is dry. Improve drainage with perlite or fabric pots if needed.

3. Heat Stress and Sunburn

In direct July sun, leaves can literally cook, especially in areas with heat indexes over 90°F. You’ll see yellowing on the top leaves, sometimes with crispy brown edges.

What to check:

• Yellowing on upper canopy
• Leaf edges curling upward
• Plants exposed to full sun all day

Quick fix:

Use shade cloth or place taller companion plants nearby to offer partial shade during the hottest part of the day (2–6 p.m.). Also, water early in the morning to help with internal cooling.

4. Pests Like Aphids or Spider Mites

Pests suck - literally. Aphids, spider mites, and leafhoppers can drain the sap out of your plants, causing yellowing and speckled damage. July is peak season for these pests to explode.

What to check:

• Undersides of leaves for bugs or webbing
• Yellow spots or pinprick damage
• Sticky residue (honeydew) on leaves

Quick fix:

Spray neem oil or insecticidal soap early in the morning or late evening (never in direct sun). For serious infestations, consider introducing beneficial insects like ladybugs.

5. Nutrient Imbalances (Especially Nitrogen or Magnesium)

By July, your plants are working hard and may burn through nutrients. A nitrogen deficiency causes even yellowing on older leaves, while magnesium issues show up as yellowing between leaf veins.

What to check:

• Older leaves yellowing from the tip inward (nitrogen)
• Green veins with yellow leaf tissue (magnesium)
• Your feeding schedule - did you skip a dose?

Quick fix:

• For nitrogen: Use a grow fertilizer high in N (like fish emulsion or a balanced veg nutrient).
• For magnesium: Add a Cal-Mag supplement or a diluted Epsom salt foliar spray.

6. pH Imbalance Locking Out Nutrients

Even if you’re feeding your plants, they won’t absorb nutrients if your soil pH is too high or low. This is a common “stealth” cause of yellowing in mid-season.

What to check:

• pH of runoff water (ideal range: 6.0–7.0 in soil)
• Random yellowing, stunted growth despite feeding
• Signs of multiple deficiencies

Quick fix:

Test your soil or runoff with a pH meter. Use pH up/down products to correct if needed. Flush the soil with properly pH’d water to reset if issues persist.

Fix It Fast Before Flowering Starts

July is a crucial time - your plants are getting ready to flower, and any stress now can reduce your yields later. The key is to observe the pattern of yellowing, act quickly, and correct the issue before it spreads. In many cases, a simple adjustment to watering, nutrients, or shade is all it takes to turn things around.

Need Help Diagnosing Your Plants?

Take a photo and compare it to common yellow-leaf issues or text the picture to HomeGrow Helpline at (937) 476-1669 & we can help you troubleshoot too. Yellow leaves in July don’t mean failure - they just mean it’s time for a little mid-season tune-up.

At Homegrow Helpline, we provide straightforward advice, troubleshooting tips, and product recommendations to support every stage of your grow - season after season.