If you were going to maintain a hydroponic nutrient solution at a steady temperature for the entire life cycle of the plant, from germination to harvest, 70-72°F/21-22°C is a good choice.
But depending on conditions, altering the temperature might be more beneficial. For germinating, as well as seedlings and clones that haven't rooted, warmer temperatures are preferred.
Aim for hydroponic nutrient solution maintained at temperatures between 70-75°F/21-24°C for faster growth while germinating and with seedlings or clones, until you can see new root growth.
Some growers say they obtain better results at temperatures as high as 78°F/25°C for water or nutrient solution temperatures during these, the earliest stages of the life cycle.
As you raise the temperature of the hydroponic nutrient solution, you provide an environment more favorable to bacteria, germs, mold, other things that can have a negative impact. It also reduces the amount of oxygen the nutrient solution can absorb.
Warmer nutrient temperatures are generally better for germinating, seedlings, clones. But these early stages of growth are when the plants are most vulnerable to organisms that will attack them.
If you are having any kind of infectious problems related to the water or if you want to prevent them, sterilize the water with small amounts of hydrogen peroxide. Instructions can be found on the germinating seeds page.
As the plant matures it will prefer cooler nutrient solution temperatures. Besides being less hospitable to things that can have a negative impact, cooler temperatures allow the solution to absorb more oxygen, which is beneficial to the plants.
For vegetative and flowering stages, aim for lower nutrient temperatures around 65-70°F/18-21°C. If the air temperature is high, lower nutrient temps help plants cool off from the heat being produced by lighting or other factors, .
Depending on the strain and growing conditions, nutrient temperatures between 60-65°F/15-18°C during vegetative and flowering stages can help the plant grow faster and keep the roots healthy white.
When the hydroponic nutrient temperature starts to get too low (or when it becomes too high) for the good of the plant, it reaches a point where it will begin to slow the development rate.
In a nutshell, initiate growth with warmer nutrient temperatures when starting hydroponic plants, until the point where you see new root and leaf growth. As the plant matures from there, you can decrease the temperature for more optimal results.
Part 01) See the full hydroponic marijuana nutrient article here.
Part 02) Nutrients and hydroponic marijuana introduction here.
Part 03) Water and hydroponic nutrients here.
Part 04) Preparing hydroponic nutrients here.
Part 05) Measuring hydroponic nutrient solution - EC, TDS, PPM here.
Part 06) Hydroponic nutrient strength here.
Part 07) Hydroponic nutrient solution temperature here.
Part 08) Flushing or leeching hydroponic nutrient here.
Part 09) Amount of water for hydroponic marijuana plants here.
Part 10) Hydroponic nutrient list of materials here.