Why Are My Cannabis Plants Not Growing? – 5 Common Mistakes

Reading time: approx. 7 min.

Growth stopped, weak leaves, or no new shoots? In over 80% of cases, it's due to these five common mistakes. Learn how to identify the cause – and fix it fast. Based on years of hands-on experience from the Cannoptikum grow team.

1. Incorrect Lighting

Too little or the wrong type of light is one of the main reasons for stalled growth. Cannabis needs specific light intensity and spectrum depending on the growth stage.

• Seedling stage: 5,000–10,000 lux – See Light Stress in Seedlings and Stretching Cannabis Seedlings
• Vegetative stage: 20,000–40,000 lux
• Flowering stage: 40,000–60,000 lux

Fix: Adjust lamp distance, set the right spectrum, and use a lux meter. Even though we don't currently sell one, it’s an essential tool for consistent results.

2. pH Outside Ideal Range

The wrong pH locks out nutrients – no matter how good your soil or fertilizer is. Ideal pH values are:

• Soil: 6.0–7.0
• Hydro/Coco: 5.5–6.5

Litmus paper for pH testing lets you quickly and easily check your nutrient solution or runoff water.

• Affordable & easy to use
• Instant results in seconds

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3. Poor Climate Conditions

Temperature and humidity heavily influence growth. Too cold, too hot, or too humid – and your plant will stall. Also see Most Common Grow Problems for more climate pitfalls.

• Optimal daytime temp: 22–26 °C (72–79 °F)
• Night: 18–21 °C (64–69 °F)
• Humidity: 50–70% in veg, 40–50% in flower

The Thermo-Hygrometer with external probe gives you accurate readings of climate and humidity – for full control of your grow environment.

• Precise temperature & humidity measurement
• Alarm function for extreme values

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4. Nutrient Deficiency or Overfertilization

Too little fertilizer leads to deficiencies, too much can burn roots. Keep nutrients balanced and check EC regularly.

➡ Learn more: Nutrient Deficiencies in Cannabis Plants

5. Watering Mistakes

Too much or too little water affects root health and growth. Overwatering limits oxygen, dryness hinders nutrient uptake.

➡ Also see: Cannabis Overwatering vs. Underwatering

“In over 80% of cases, growth problems are due to pH or climate. Check these two factors first before thinking about nutrients or lights.”

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