Temperature Control

 

From planting your first seed to harvesting your first crop of buds, getting the temperature right is paramount and it is a topic that warrants special attention. As previously discussed, there are several factors within your grow structure that can result in a change in temperature. (We could put a link here to this) Equally important is understanding the changes in temperature necessary at each stage of the growth cycle.

 

Seedlings and Vegetative Stage

 

Both seedlings and younger plants in the vegetative stage do best in the range of 20-30°C (70- 85°F) during the day when lights are on. Seedlings in particular have a tendency toward more rapid growth with slightly higher humidity levels and warmer temperatures, but both prefer slightly cooler temperatures at night (when lights are turned off). Even though you should be increasing and lowering the temperatures during the day and night cycles, you still need to keep them within the specified range recommended for seedlings and younger plants.

 

Flowering Stage

 

When plants begin to bud (flowering stage), it is recommended that you keep the temperature slightly lower at 18-26°C (65-80°F). This will produce the best smell, colour, and trichome.

TRICHOME TIP

 

When speaking about cannabis, trichome does not refer to the tiny hairs on the plant stem or leaves. In the case of cannabis, trichome are those tiny crystals that cover the buds and leaves of some cannabis strains. They actually carry the wonderful smells you have come to know and are typically sticky and shiny. This trichome are responsible for producing the multitude of cannabinoids, flavonoids, and terpenes that make the cannabis strains unique and potent.

The colder the temperature, the slower the plant growth is. Take care when lowering temperatures as anything lower than 15°C (60°F) can shock plants and freezing temperatures can kill the plants. Cooler temperatures also invite the possibility of mold especially if your grow space is also too humid. Cannabis plants do not take well to large fluctuations in temperature as it can reduce photosynthesis and an ‘over-purpling’ of its leaves. Also keep in mind that plants grown indoors are more sensitive to the cold than those grown outdoors.

Although temperatures that are kept too high will not typically cause plants to die but their growth will be considerably slower. Anything above 26°C (80°F) during the flowering stage will reduce the smell and potency of the buds as well as slow down growth. The flowering stage is probably the most important time to keep a watch on temperatures and keep them as consistent as possible.

Temperatures that are kept too high are also vulnerable to a number of problems such as:

  • Root rot
  • Spider mites
  • Nutrient burn (due to an increase in water transpiration)
  • Wilting
  • Mildew (white and powdery, especially when combined with excess humidity)
  • Reduction in proper smell (Terpenes often burn away due to higher temperatures)

Cannabis plants can thrive quite well with grow lights that are 600W HPS or slightly more as long as temperatures do not exceed 30°C (80°F) even without added C02 enrichment. Just remember to keep an adequate air flow and consistent low humidity.

 

CO2 Enrichment

 

If you supplement your grow room with CO2, you will want to increase the temperature but remember these important tips if you decide to do this:

  • Ensure that your grow room is completely sealed
  • Maintain at least 1500 PPM of CO2 in the air
  • Temperatures must be between 30°C (85°F)

 

TIP

 

Although temperatures that are slightly warmer at night will decrease your plant growth, it can be a good tool if your plants are growing too tall since higher temperatures at night affects upward growth.

 

Some Effects of Temperature

 

  • Correct temperatures are most critical during the drying and curing process. It plays a key role in producing top-shelf bud.
  • Increasing night time temperatures will decrease ‘upward growth’ of plants. Slightly cooler night time temperatures will result in faster growth.
  • Temperature has a direct effect on your grow rooms relative humidity.
  • Certain changes in temperature will alter the smell and taste of your buds.

Relative humidity (RH) and temperature directly affect each other and, in some cases, altering one can correct a problem with the other. It is important to understand what ‘humidity’ and ‘relative humidity’ mean and the difference between them.

Humidity – relates to exactly how much water is contained within the air.

Relative humidity – is the comparison between the amount of water in the air and the maximum amount of water that the air can hold at the current temperature. (i.e. Warmer air can hold more evaporated water than cooler air)

Although plants are able to flourish nicely at various relative humidities, if the air is overly saturated with water, you will see films of water or dew on the leaves which will result in mold.

 

INTERESTING FACT

 

VDP – Vapour Pressure Deficit measures both the temperature and relative humidity. This is a greenhouse term used to determine the ideal VDP range. Most plants prefer VDP’s from 0.8 to 0.95 kPa.

 

DRYING AND CURING STAGE

 

All the time and effort you have put into growing your own cannabis plants are finally paying off and you are now ready to dry and cure those buds. While you should be feeling a sense of accomplishment, keep in mind that about half the quality of the final product will be determined by this last stage!

Maintaining the right balance between temperature and humidity at this stage will ensure you end up with a product that is smoother to smoke, more potent and has that distinctive ‘sticky’ feel. Making sure you keep the right balance between temperature and humidity during this stage also means you need not be concerned with over-drying or problems with mold.

 

GROW LIGHTS AND TEMPERATURE

 

CFLs and other fluorescent Lights – One of the great things about CFL lights is that they produce a very low level of heat and can therefore be placed quite close to your plants. They are also easy to find in any hardware store for relatively low cost. Unfortunately, if you want to increase your yield, you will have to keep adding more of them and the heat they give off will begin to increase. One or two cannabis plants should be the most you grow under CFL’s. If you are planning to have more than a couple plants at one time, you should consider switching to small HPS grow lights

Characteristics of HID GROW LIGHTS – (MH AND HPS) – MH (Metal Halide) and HPS (Hight Pressure Sodium) lights do generate a lot of heat and typically use quite a bit of electricity. On the other hand, the smaller models of HID lights produce considerably less heat. Many growers tend to go with CFLs trying to avoid excess heat in their grow room. However, 250W of HPS light produces approximately the same amount of heat as a 250W CFL. And remember that HID lights will not only give you more light but also better yields. An important advantage of using HIDs instead of CFLs is that the higher-end HID models do come pre-built to allow for cooling via an exhaust system. CFLs are recommended when your grow room does not have a lot of height since HIDs require more height.

So, it is obvious that temperature plays a vital role in all stages of the cannabis plant from seedlings, to vegetative to flowering all the way to drying and curing. In fact, temperature is most often the deciding factor between a successful harvest and one that never quite makes it. We also see that temperature and humidity are inter-related. Issues with temperature are typically the result of improper lighting and inadequate air flow. Make certain that you understand the things that can affect the temperature within your grow room. If this is your first attempt at growing cannabis in an enclosed structure, it’s best to start small and keep things as simple as possible. Once your first crop has been successfully dried and cured, the lessons you have learned will propel you to expand your grow room, if that is your goal. It is always a good idea to make notes of things you have done along with what has worked and where you need to change things up a little. Above all, remember to have fun with this endeavor and ultimately enjoy the fruits of you labor!