Late flowering
In the second part of the flowering phase the humidity level must be reduced to 40-50%. In the two to three final weeks it's preferable for this figure to be closer to 40%. This is absolutely essential, particularly if you're growing strains that are sensitive to mould or that produce dense flowers.
The Flowering Stage: Best Grow Room Temperature
The best grow room temperature during the flowering stage of growth is 68-75 degrees during the day and no more than 10-15 degrees cooler at night. If you're supplementing with CO2, daytime temps can be as high as 75-82 or so.
The ideal daytime range in flower should be between 72 and 85°F, while the room can drop to as low as 55 to 70°F at night.
Having temps above 80°F in the “bloom rooms” can reduce the potency and smell of your buds. Excessive temps also make the plants more susceptible to spider mites, powdery mildew, root rot and nutrient burn. This is especially true if the humidity is too high as well.
Best grow room temperature for the flowering stage
At night, it should not be more than 5-10 degrees cooler than 82-86 degrees during the flowering stage. You can have daytime temps of 72-81 if you supplement with CO2.
Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation. Severe or hard freeze - 25° Fahrenheit and colder causes heavy damage to most plants.
Generally, pot plants in their vegetative stage prefer a temperature in a range from about 68 to about 77 degrees Fahrenheit. When they are flowering, cannabis plants like a range of about 65 to 85 degrees Fahrenheit.
Plants can tolerate lower humidity as they move through the flowering period. We like to keep our RH at 65% for the first week of flower. This minimizes plant stress during a naturally stressful part of their life cycle. Between weeks three and eight, we gradually lower the RH.
The greater the difference between the day and night temperatures, the more elongated the plant's cells become, and some plants also produce more nodes when the temperature fluctuates dramatically. The number of elongated nodes in the stems make the plant taller.
Generally, you want to water every 2 or 3 days during Flowering and you want to water enough that 10-20% of water comes out from the pot as runoff. You can check your soil moisture by sticking a finger in the pot: if the soil is dry a couple inches down, then it is time to water again.
The Final 2 Weeks Of Flowering. If you grow strains with an average flowering time, the majority of bud development will occur by the 6th week of bloom. In the last two weeks, the buds will mostly be ripening and not really growing much more in size.
If you live in a warm climate, late summer temperatures can reduce flowering, as most traditional summer annuals do not like temperatures above 90F during the day or night temperatures much above 60-65F.
Ideal indoor relative humidity levels can range from 70% in the seedling stage to as low as 30% during the flowering stages. That's why it's important to deliver a wide range of indoor humidity throughout the growing process.
The ideal humidity level during the flowering stage is between 40 and 50%. This is because the flowers need to be able to absorb water through their petals, and if the humidity is too high, the flowers will be too wet and won't be able to absorb the water.
60 humidity is not necessarily too high for flowering, but it is on the higher end of the recommended range. Nearly three-fourths (73%) of respondents said the optimal humidity level in flowering rooms is 40% to 55%.
Too little humidity in the grow room isn't good for plants either: Growth will become stagnant- If your plant feels it will become dehydrated, it can also result in the closing of the stomata, which means the plants won't be able to take in much (if any) water.
When conditions are too humid, it may promote the growth of mold and bacteria that cause plants to die and crops to fail, as well as conditions like root or crown rot. Humid conditions also invite the presence of pests, such as fungus gnats, whose larva feed on plant roots and thrive in moist soil.
Data from published works concluded that the plant growth improved with increasing humidity, as higher humidity conditions help to keep the stomata open to maintain the photosynthesis process and minimize evaporation process of the plants.
In these cases the low temperature at the end of flowering has affected the plants, provoking a very notable color change and an increased trichome concentration on the buds.
Signs Your Plants May Be Too Cold
The leaves brown and fall off. If your plant is too cold, it may begin to die, and its leaves will brown and fall off. The leaves turn yellow.
Flowers are happiest in temperatures of 40-50 degrees. Most of my flower coolers are about 36 degrees.
With that in mind, experts generally recommend flowers and other houseplants be brought inside or otherwise protected before the thermometer dips below 45 degrees Fahrenheit. For warmer-weather and tropical plants, that threshold is a bit higher, at around the 50-degree mark.
A tender plant is one that will not survive the winter unprotected because it's sensitive to frost. Some will cope with cold, but not when combined with wet - for example, agaves (below) - and others dislike cold winds. Tender plants generally won't survive the winter without some form of human intervention.
Managing grow tent heat is one of the more difficult, frustrating aspects of indoor growing. Not too hot and not too cold; many of the plants we grow are just like us and prefer similar temperatures - between 65 to 85 degrees Fahrenheit.