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ideal temps & humidity to germinate cannabis seeds

Placing an exhaust fan in the ceiling vent of your grow tent is also highly effective at reducing heat. After all, heat always rises to the top.

Reducing heat levels in a grow tent can be much harder to control than the reverse. We recommend using electric fans to circulate the air as much as possible to disperse the heat and thus cool the young cannabis plants.

The optimal conditions for cannabis seedlings are a sunny, warm (20-25ºC) and humid environment with well-circulated air. Their underdeveloped root systems mean that seedlings need to be exposed to lots of light and heat. Problems arise as their immaturity means that they cannot withstand high temperatures. Therefore, we recommend that growers maintain 20ºC to 25ºC indoor environments when the lights are on.

Temperatures that are too cold

It is also a good idea to lower humidity levels to about 40 percent to 50 percent, especially during the late flowering phase. This encourages the production of highly-prized resin and a higher terpene content leading to a more aromatic and flavourful crop.

When deciding the correct temperature for your plants, therefore, it is also sensible to assess the humidity levels as the two go hand-in-hand. To do this, you should invest in a good-quality thermometer and a hygrometer, ideally digital models with the ability to store historical maximum and minimum levels.

Temperatures that are too cold will slow down a cannabis plant’s metabolism and its roots system will become increasingly ineffective. If temperatures drop below 12 degrees, the plant is even at risk of death.

However, the temperature must not fall to less than 20 degrees Celsius nor rise to more than 30. If you are using a greenhouse for the germination phase, be warned that it can get sweltering so you must regularly monitor the temperature. Humidity must also be continuously monitored. If the seed trays dry up, germination will not take place or recently sprouted shoots will wither and die. You must not forget to add water when necessary – a spray dispenser is gentle for this, but you should not give them too much water. The seeds should only be soaking wet during the first two days.

Three fundamental principles will trigger that first small taproot to appear: warmth, moisture, and darkness. With the promise of moisture, a single root will take shape before slowly developing into the cannabis plant we know and love. In the right conditions, seeds will begin to develop within 12–36 hours of moisture being introduced to them.

Start by filling pots with a premium-quality soil that has been soaked in water. Many growers also choose to lace the water with a root stimulator. Make a hole roughly 10–15mm deep. This will be your seed’s new home. Remove the seeds from their packet and place them into the pre-dug holes. Loosely cover the seeds, but be careful not to compress the soil above the seed too much. The root will struggle to penetrate solid soil, slowing plant growth. Lightly spray the top of where you placed the seed so that your growing medium stays moist.

WHAT IS AN EXPECTED GERMINATION TIME?

Your growing pots will need to be placed in a damp climate that is within the temperature range listed under our golden rules. After 4–10 days, you should see a young seedling sprout, while the roots will have begun to develop underneath the soil. The entire plant and its soil can now be transferred to a larger pot, where normal growing routines should start.

To avoid disappointment, seeds that have a darker colouration stand a better chance of germinating, while pale green or white seeds are likely to fail. Even if dark seeds look slightly damaged, they should be planted anyway. There is a good chance they will still germinate, even if the outer shell is somewhat crushed.

Probably one of the most common methods of germination. The kitchen towel method comes in several iterations. Some growers use cotton wool pads or absorbent pieces of paper. For this guide, we will be using kitchen towel as it is readily available and holds moisture relatively well.

This Indoor Grow Garden includes reusable trays that can grow the plants for a week until transplanting into a bigger pot. The trays sit beneath 2x2ft 24W fluorescent bulbs for healthy growth. This setup provides light & warmth, it also ensures that fresh air & average humidity levels prevent negative factors from disturbing germination. The lights are housed in the canopy of a sturdy aluminium stand that has an adjustable height (up to 38cm H from base) and a reflective hood to maximize usable light. There are many different models of fluorescent or CFL fixtures on the market to suit every taste and budget. Give seedlings maximum light to prevent stretching and support fast development. Use additional light from a window if available. For best results we recommend HPS lamps from the start. A 70-150W HPS lamp does not use more electricity than standard CFL lamps but provides much more lumens (light intensity). If you are growing with 250-600W HPS then you should germinate or put your seedlings under the lamp as soon as possible to ensure quick and vigorous growth.

Within 3-7 days the seedlings should appear out of the soil/rockwool cubes.

IMPORTANT: Don’t cover pots with plastic wrap, don’t use a humidity dome to seal off the pots, or place pots/rockwool cubes in a propagator that’s completely covered! This prevents fresh air exchange, raises humidity to excess levels, and easily facilitates the spread of fungus. The seeds will rot before they can germinate. Excess humidity combines with lack of oxygen is the #1 cause for poor germination results!

What happens if one uses pre-germination methods?

As soon as the first pair of leaves grow on the seedlings transplant them into 14-16 cm/5,5-6,5” pots, so that they have sufficient space for their root development and nutrients. You can also choose larger containers if you are confident that you will not over-water. We recommend a 4-5L/1 gallon container for the first 4 weeks of growth and subsequent period of sexing under 12/12. Repot females into larger containers after sexing. See our SOIL GUIDE for info on container sizes.

Cannabis is not an orchid or swamp plant! The seeds need a well aerated growing medium to germinate well. Seedlings also cannot tolerate high humidity and can easily be attacked by fungus such as fusarium and pythium. Only the soil or growing medium should be moist for optimal germination and seedling growth. Ambient humidity is best at or below 50%.

Please note: Cannabis seeds are a biological product. We therefore do not carry responsibility for germination rates once the seeds are dispatched to the resellers or customer. The reseller and customer is responsible for proper storage and handling of seeds.

Humidity domes are only required for rooting cuttings.