Posted on by Alex Russell

Temperatures

Temperature is important in every phase of a plants life cycle.

Most hydroponic gardeners have encountered this topic and generally revisit it as a reference guide, the downside for a lot of us, is budget. Some items like climate control and recirculating chillers are quite expensive and if they are not an option then we have to be resourceful, so this article is solely focusing on the basics and the things we need to do manually.

Things that can be affected due to incorrect temps:

  • Root-zone
  • Dissolved Oxygen (DO)
  • Reservoir
  • Environment
  • Leaf surface
  • Plant health

 

With so many variables to monitor it is key you develop a rough understanding before you start growing, some learn better in real-time situation so, for some the understanding will be formed when they can see the results in front of them. Either way, go for it.

 

RESERVOIR, ROOT-ZONE & DISSOLVED OXYGEN 

A majority of hydroponic systems contain a root-zone suspended in a nutrient solution. One of the reasons the temperature of the solution is important is because the roots are reliant on oxygen in conjunction with moisture to help develop a strong anchor, the more oxygen in the presence of an adequate food supply will result in fast healthy root growth, which in turn impacts plant growth. The higher the temperature of a nutrient solution, the less dissolved oxygen that can be held in the water, with lower temperatures being able to hold more DO.

RZ & DO Temps: 17c - 22c (63 F – 72F)

 

ENVIRONMENTAL & PLANT HEALTH 

Environmental temperature indoors can become a fine art of controlling fluctuations, humidity and external forces, while outdoor temperatures you are usually at the mercy of mother nature.

Here is a revision of some of the most optimal environmental temperatures for various stages of commonly grown plants, with there being obvious exceptions to these 'guide' temperatures.

 

Seed Germination: 24-27 °C - 75.2-80.6 °F

Seed Germination is an essential part of the plants life, if temperatures fluctuate and don’t remain consistent temperatures your seedling will struggle and will not have a ‘perfect’ start to life which will affect: Growth rates, Plants overall health and overall end yield. 

 

Clones or Cuttings: 24-26 °C - 75.2-78.8°F 

Clones or cuttings require the same temperature as seedlings.

25 °C - 77°F is perfect for all varieties causing your cutting to root much faster than colder/warmer or unstable fluctuating temperatures.

 

Vegetating/growth: 23-29.5 °C - 73.4- 4°F

Vegetating plants grow very fast in the right conditions, there is a big difference in this phase due to different expressions in characteristics.

If you are after a the ‘colour fade’ harvest pushing the temperatures lower will help your specific outcome (Keep in mind not every variety will change colour)

If you are growing a longer flowering variety then they require slightly more heat due to them originally coming from around the equator where it is much warmer so we would grow these specific varieties at around 27 °C - 80.6°F.

If you are growing a 8 week strain optimum temperatures are closer to 25 °C -27°F due to the strain originating further from the equator

 

Flowering/bloom: 22-28 °C - 71.6- 4°F

As we transition our plants into the flowering/fruiting phase of their life cycle, the temperatures should roughly stay similar to the vegetive period depending on your variety and the outcome you are trying to achieve.

If you are growing a longer flowering variety, starting flower at 25 °C - 77°F and ending closer to 28 °C – 82.4°F is ideal.

 

Drying: 18-21 °C - 64.4- 68°F

This particular phase is very important! 

Too high in temperature and your flowers will be significantly less potent less and much less aromatic.

Consistent temperature stability in the drying phase is what we call a ‘slow dry’ and is much better in my opinion for holding all the essential oils inside the flower. 

Too fast of a dry and your flowers will be more crispy/crumbly much less potent and less aromatic. Dry at these temperatures for 4-14 days depending on flower structure and size.

 

Curing/storing: 18 °C - 64.4°F

Once you are this stage, make sure your flowers are dry and the stems snap or rapture when bent, because if you start curing with dampish bud you will have mould in no time. Keep at a consistent temperature with burping your jars (opening removing old air) for the first 2 weeks after this time the flowers will be much browner and from here your smell and taste of your flowering will majorly increase. 

 

LEAF SURFACE TEMPERATURE (LST)

Unfortunately this is not an easy question to answer, as there is too many additional variables that play a part in this. Many factors, such as: plant type, concentrations of CO2, strains variations, etc. all factor in determining the exact optimal LST.

For many plants, the leaf temperature range for photosynthesis would be between 15c celsius and 30c celsius (59F - 86F) on average with normal atmospheric concentrations of CO2, this range would increase as the levels of CO2 increased within the environment. This temperature range is basically what your plants core temperature should be for healthy, stress-free growth as LST is a good indicator of your plants core temperature, although not always exactly matching.