How to Manage the Humidity in Your Grow Room

How to Manage the Humidity in Your Grow Room

Getting your environment correct is the key to successful growing, and humidity is easily one of the biggest factors. Perfect it and you'll see a huge impact on overall plant health. In this blog, we explain why humidity plays such a big role, and showcase the equipment that you need to get it spot-on.

When water and nutrients are absorbed through the rootzone, they are transported upwards via xylem cells and distributed to the areas that they are needed. Ultimately, though, 97% of the liquid that's taken onboard is lost through stomata – the tiny pores found on leaf surfaces that facilitate the exchange of gasses for the process of photosynthesis. Plants live in a perpetual cycle of acquiring and losing liquids, and for this reason, it is essential that the correct balance is maintained at all times. To complicate things further, this balance isn't just a product of activity within the plant, but it is also dictated by the conditions within the room (or outside area).

  • If the surrounding atmosphere has moisture levels that are too high, then plants will hold onto water more easily.
  • If the surrounding atmosphere is too dry, then plants will transpire (lose water) more quickly.

An upshot of this is that your environment will have a huge impact on the way that your plant uses nutrients. When plants transpire too heavily, you'll notice that the nutrient solution in your tank becomes more concentrated. That's because the plant has used up the water from your nutrient solution and left behind an excess of minerals, increasing EC levels. If left too long, this will inevitably damage roots, stunting growth and causing irreparable damage to the top half of the plant.

Conversely, if your room's humidity is too high, then your plant is going to have trouble uptaking the nutrients that it needs. That's because, if the plant loses less water through stomata, then in turn, less nutrient solution will be absorbed by the roots, leading to deficiencies.

Further to this, high humidity levels massively increase the risk of encountering mould related issues like powdery mildew – a fungal disease that infects plants, slowing growth rates and compromising yields. Botrytis (otherwise known as 'bud rot') is another fungal pathogen that destroys fruits from the inside out, making it a difficult disease to spot. These two issues alone can completely wipe out entire crops and undo months of work!

So it's pretty clear that humidity levels play an enormous role in deciding the fate of your indoor garden. Success or failure will depend on getting your humidity (along with temperature) within optimal regions. Get this sorted and you are well on the way to bigger and better yields!

So what are the right humidity levels to aim for? To truly perfect your environment, you'll need to look at VPD (vapour pressure deficit) levels, but to keep things nice and simple, we'll work with some rough averages, assuming that your daytime temperatures are sitting around 25°C. If you want to skip straight to the more complicated stuff, you'll find more info on VPD here.

  • 80% Clones
  • 65% during vegetative growth
  • 50% flowering

Achieving an 80% humidity level during the cloning stage is actually pretty easy. Keep your unrooted cuttings in a propagator and use the adjustable air vents to allow moisture to escape as needed.

During vegetative growth, plants are still small in size, transpiring little. To get your environment into the 65% sweet-spot, you may well need a little help - and this will come in the form of a humidifier.

For growers operating on a larger scale, the  HR-50 humidifier does the job nicely. It comes with a hygrostat, allowing you to add moisture as and when it's needed, covering an area of 150m2.

The SonicAir Pro is another premium humidifier from G.A.S. It uses ultrasonic technology to output up to 6.5 litres of water into the air per hour!

It's important to note that if you use plain tap water with your humidifier,  it will eventually leave mineral deposits on the surfaces of your equipment.  Using tap water with humidification equipment will eventually damage them. You'll notice that the salt deposits have completely corroded the reflective surface, promoting rust and decay. The issue can be solved relatively easily by running humidifiers with reverse osmosis water, which has an EC reading of zero.

During the flowering phase, plants reach full maturity, roughly doubling in size from the time they are first switched to a 12/12 cycle. To facilitate this growth, they will naturally use more nutrient solution. The overwhelming majority of the water that's added to your reservoir tank is going to be released into the room as vapour. And this all happens at a time when you need to keep humidity levels down... Fortunately, this issue can be negated by using a dehumidifer. Dehumidifiers work best in closed loop systems because they don't have to fight against the effects of your extraction fan(s), but they can still be useful to those growing without air conditioning.

Many customers use dehumidifiers to keep humidity levels in the sweet spot when drying and curing large quantities of plant material. Doing so helps organic compounds, like chlorophyll, break down fully for a superior end-product. If the humidity is too low then plant matter dries out too quickly, affecting consistency and flavour. On the flip side, if humidity levels start to creep above optimal limits, then the likelihood of encountering mould is increased dramatically.

Whatever the application, we stock a range of dehumidifiers that are up to the job!

For those operating on a larger scale, Quest dehumidifiers are ideal. They are built to military-grade specifications and are used in major industries, onboard aircraft carriers and even inside submarines. They are trusted for use in high-intensity environments, and you won't find a better constructed unit out there.

The Quest 70 and Quest 155 Overhead Dehumidifiers pull 26 litres and 75 litres from the air respectively, per day.

There's also version called the Quest portable dehumidifiers that are easier to transport, making it ideal for moving between multiple locations.

Don't forget that our staff are always happy to talk you through it if you need any help or advice. For more info, give us a call on 01782 749955 or drop us an email at 

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