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Localised Heating To Aid Root Formation During Winter

Localised Heating To Aid Root Formation During Winter

Hytec Horticulture |

It’s a challenge keeping your leafy friends warm in winter when cold air finds its way through every nook and cranny. Winter is in full swing, and you may be noticing that your grow room is just a tad too cold for your plants. It may be time to look into adding a heating source. No matter if your grow room is set up in an outdoor hoop house, greenhouse, or your basement, there are heating solutions that will work to keep your plants at a pleasant temperature that will keep you growing all season long.

The optimal temperature for hydroponic cultivation is between 20°C and 25°C, ideally at 24°C. Through extraction and ventilation, the temperature of the grow tent is controlled to a certain extent; maintaining a good temperature is difficult in summer when the ambient heat is added to that of the propagation lighting or during winter when increasingly changeable weather affects external conditions. Good substrate warming conditions are essential for smooth root formation at all stages of plant development.

Two solutions: use an air conditioner or trigger the lighting phase at dusk for summer or make a smart move and install one of our Oil-Filled grow room heaters to help maintain stable grow room temperatures throughout the cold, dark months of autumn and winter. In fact, there’s no guarantee that you won’t need the precious heat output from these units at times during the spring and summer too always try to maintain your grow room temperature around 24°C.

Maintaining root temperature is the basis of a beautiful and vigorous plant; therefore, for an ideal root formation, we will retain these 2 rules:

  • High temperatures will have a negative impact on the aeration of the nutrient solution. The plant will be more susceptible to root pathogen attacks.
  • A substrate that is too cold will not favour the removal of minerals and water needed by plants and increases the risk of developing pythium, also known as "damping-off".

Species grown in hydroponic systems are mostly plants that require heat during germination (tomatoes, cucumber). The emergence will be rapid with a substrate temperature between 20 and 25 ° C.

The cuttings (un-rooted) will easily acquire a root system with a temperature of 21 to 25°C and a hygrometry close to 100%. With these conditions, the cuttings quickly develop roots to collect water and nutrients in the substrate.

Localized Heating During Long Periods Of Cold

Localised heating to the root system, from a heated carpet or cord, will promote an optimal heating of the substrate, and consequently, high-quality root formation. When growing in Rockwool, the heating allows a rapid warming of the substrate, especially in winter.

These electrical resistors are insulated by a layer of silicone, and consume about 10W per meter of heating cable (in 220V). In professional horticulture, even if this type of heating is limited to small areas (in multiplication), they are supplied with a low voltage (24V). The heat is directly emitted to the substrate and the plant in the form of radiation conduction or convection.


The cable can be placed under the culture tray to warm the substrate and the nutrient solution (in the case of closed circuit culture), or directly under the substrate if the cable is insulated. In this case, it is preferable to use a thermostat that allows an adjustment of the electrical resistance at a temperature below 30°C so as not to burn the roots.

The main disadvantage with this localized heating to the roots is that it increases the evaporation of the substrate; therefore, the horticulturist must ensure the regular supply of nutrient solution. An excessive temperature in the substrate can lead to salt precipitation problems. In this case, it is necessary to decrease the temperature of the heating and to reduce the concentration of salts (decrease of the EC).


The temperature that you need in your grow room is going to depend on what you’re growing and your current set-up. Once you determine what temperature you need to try to reach, you’ll be able to personalize your heating plan based on your needs. You may find that you need to mix and match some of these options to get the right level of heat in your grow room.