Tips and Tricks

Dehumidifier – Slightly raises temperature, dramatically lowers humidity
Space Heater – Raises temperature, lowers humidity
Reverse cycle air conditioner – Lowers temperature, lowers humidity
Evaporative Cooler – Lowers temperature, dramatically raises humidity
Humidifier – Raises temperature (somewhat), raises humidity

Plants growing in the vegetative stage like it warmer (28-32°C), they love heat as long as they have a humidity of approximately 60 to 70%. When plants are small they don’t produce much humidity within a grow room or greenhouse, to offset this until plants get larger an evaporative air conditioner or humidifier is recommended and/ or reduced outlet fan strength. As plants get larger they produce a lot more humidity, increasing outlet fan strength is recommended to be able to lower the humidity.

Plants In the flowering stage love a cooler climate (25-27°C), this ensures that the plants can perform at their optimum, heat will stress your plants out, they start just trying to survive instead of thriving. Heat can open the flowers up and cause regrowth of leaf, this is definitely something to avoid, cooler temperatures in the flowering stage helps to produce tighter compacted bunching of flowers and the highest oil production.

All ways keep in mind micro-climates e.g. The temperature at the wall where your temperature gauge is may have a different temperature compared to a foot below a globe that’s on, or the side of a room compared to the middle of a room. An (8°C) cooler dark period is optimal in the grow and flowering stage, a 40-50% humidity is recommended as bud rot in large flowers is a common and an expensive problem to experience along with the accompanying emotional and financial turmoil.

Colder temps will slow and stunt growth, temps lower than (15°C) can disrupt plant metabolism and growth, freezing temperatures will shock or possibly kill plants. Some plants continue growing in the cold without obvious signs of stress, but they often don’t yield as well, purple stems and slow growth are primary signs.

High temperatures will cause plants to suffer and become stressed, firstly too hot can cause burning of the foliage as the plant can’t keep up with respiration and there’s a risk of under watering, in this case plants will use more water from the medium and leave behind extra salt which will build up adding to the burn. Too hot in the grow period can be advantages for genetically bushier strains as it causes the plant to stretch (60-70% humidity), this can be done on purpose along with raising the lights as the plants stretch for the light. In the flowering stage heat is disastrous and must be avoided.

Please note temps above (27°C) in the flowering stage will harm flower growth and may cause them to become airy and loose with regrowth of leaf, this must be avoided, tightly compacted flowers are the desired outcome, a simple way to remember is that heat expands and cold contracts. The heat can also reduce the quality of the crop as oil production is lowered.

Maintaining climate control for your grow room is one of the most crucial aspects of growing and is essential to maximise your ISN nutrient system.

Too much heat can lead to many problems, including spider mites, white powdery mildew (especially if it gets humid, too), root rot, nutrient burn (from increased water transpiration), reduced nutrient uptake, wilting due to root oxygen deprivation.

In heat waves without adequate environmental controls; it is better to turn the lights off for a night or two (only in flower) or reduce light wattage and/or raise lights (reduce feeding to match), babying your plants at this time can pay dividends, the leaves may get darker during this resting period as chlorophyll production increases as plants try to absorb more light.

Water Chiller

Best way to cool a reservoir: A Water Chiller.

While this method is the most effective and reliable, its also the most expensive. Depending on your growing location and climate, this may be your only option if you wish to grow through the summer months with any real significant reservoirs.

Insulating your Reservoir

Simple and cheap adjustments, such as painting or wrapping your reservoir in Mylar or white reflective surface covers can drop your temperatures down for very little cost.

Increase your Reservoir Size

A smaller reservoir will heat up significantly faster than a larger reservoir, as more water will take longer to heat. With good insulation and a large reservoir, it should buy you some more time to get through a hot day without as much of an increase in temperature.

Remote Reservoir Location

Storing the reservoirs away from the area with much greater environmental control, pumping to the room.

This is a problem in colder climates, winter. One of the first visible symptoms are purple stems very dark leaves, which is probably caused by a deficiency of phosphorous (this element is poorly assimilated at 15ºC, and won’t be assimilated at 10ºC). The growth of the plant is stopped and soon deficiencies of other elements will be observed, like magnesium or nitrogen.
During bloom, this problem usually results in poor flower development, although oil production is normal in many occasions , the size of the flowers will be much smaller and they’ll develop much more small leaves. To avoid it, we just have to use a simple water heater, which allows us to raise the water temperature

Dehumidifier – Raises Temperature (somewhat), Lowers Humidity
Space Heater – Raises Temperature, Lowers Humidity
Air Conditioner – Lowers Temperature, Lowers Humidity
Evaporative Cooler – Lowers Temperature, Raises Humidity
Humidifier – Raises Temperature (somewhat), Raises Humidity

Temperature and relative humidity are closely related to each other.

Relative humidity is measuring how much water is “being held” in the air compared to the maximum amount of water that can be held at that temperature.
Warm air can “hold onto” more water than cool air. Plants will tend to thrive at different relative humidities depending on the temperature of the air. Once the air becomes too saturated with water, it will tend to form dew or films of water over leaves, which leads to mold.

If the air is too hot and dry (high VPD), plants will tend to have curled up leaves and stretched growth.
If the air is too cool and humid (low VPD), plants are more prone to problems with mold or fungus disease.

Grow Phase
40-60% RH if you see wet spots forming on the leaves, humidity is too high or you need to increase air circulation and air exhaust out take.

Bloom Phase
40-50% RH less humidity helps protect plants from mold – during the last few weeks of flowering, a lower RH and colder temperatures can possibly increase oil production.