A successful grow starts with healthy, rapid germination – and the key to that is the right temperature.

If you're just starting to germinate cannabis seeds or simply want to improve your germination rate, this article will help you understand why temperature is so important, what the ideal values are, which mistakes to avoid and how to optimize your germination environment.

Why is temperature so important during germination?

Germination is a biological process during which the seed shell cracks and the first root tip (radicle) emerges. For this to happen, the enzymes inside the seed must be activated – and this requires a certain temperature.

At too low a temperature, the process slows down or stops entirely; at too high a temperature, the cells may be damaged or even destroyed. The ideal temperature activates metabolism and allows the seed to swell, followed by root emergence.

What is the ideal germination temperature for cannabis seeds?

Cannabis is a heat-loving plant – this applies from the very first stage, germination. The optimal germination temperature is between 22 and 25 °C, kept stable.

Temperature Range	Expected Germination Effect
< 18 °C	Very slow or failed germination
18–21 °C	Slow, uncertain germination, increased mold risk
22–25 °C (ideal)	Fast, healthy germination within 1–3 days
26–28 °C	Still viable, but higher risk of drying out
> 28 °C	Stress, halted germination, risk of fungal growth

Tip: It's not only the air temperature that matters – it's the temperature at the germination site (where the seed rests, e.g. on paper towel or in a peat pellet). It's worth measuring this separately!

How to ensure the ideal temperature during germination?

1. Choose the right location

• Place the unit containing the seeds (e.g. moist paper towel, Root Riot cube, etc.) in a warm, draft-free, dark place – such as a cupboard, shelf or mini greenhouse.
• The ambient temperature should never drop below 20 °C, as this may hinder germination.

2. Use a heating mat with a thermostat

• It is best to use a heating mat with temperature control that maintains a steady temperature around 24 °C.
• Place it under the germination container; if needed, place a towel in between to avoid overheating.

3. Use a thermometer (and hygrometer)

• Check the temperature near the seeds daily – not just the general room temperature.
• A combined temperature and humidity meter helps keep the environment stable.

 

Common mistakes to avoid

• Germinating on a windowsill in winter
  At night, temperatures can drop drastically – the seed may "freeze" and fail to germinate.

• Placing seeds directly on a radiator or in direct sunlight
  Excessive heat can damage the inside of the seed – the medium dries out and the sprout may die.

• Fluctuating temperatures
  Alternating warm and cold conditions (e.g. a heating mat without a thermostat in a cold room) disrupt the germination process. Cannabis seeds need a stable environment!

 

What about humidity?

Although this post focuses on temperature, humidity is just as important. The ideal humidity for germination is between 70–90%.

In too dry air, the medium dries out and the seed cannot swell – it will die. Use a sealed container, mini greenhouse or resealable bag and ventilate once daily to prevent mold.

How long does it take for a cannabis seed to germinate at the ideal temperature?

 

• Within 24–72 hours: the first root tip appears
• Within 3–5 days: ready for planting
• After 7 days: something is likely wrong (incorrect temperature, old seed, too wet or too dry medium)

And what happens after germination?

Once the root tip emerges and the seed is planted, you should continue to maintain the temperature between 22–25 °C. At this stage, light is also essential – without it, the sprout will stretch excessively.

• Many growers slightly lower the temperature to 21–23 °C at this point to encourage more compact and stronger plant development.

 

Summary – The key to successful germination is temperature

• Keep the temperature between 22–25 °C,
• use a heating mat with a thermostat,
• and regularly monitor the environment.

Further recommended reading:
Are you just starting to grow or about to germinate seeds? Don’t miss this essential beginner’s guide:
How to germinate cannabis seeds successfully – even as a beginner

This article walks you through the most reliable germination methods step by step, so your plants get off to a strong start from the very beginning.

Written by: Bartholomew Alen