This is a short article for those wondering the relative humidity (RH) requirements for each stage of a plants life cycle.
Let’s start from the beginning of the plant cycle:
Seed Germination: 72-100%
We need the air to be moist so the hard seed shell can soften, this allows the radicle to emerge that will later become the main/primary tap root.
Clones or Cuttings: 68-85%
Clones or cuttings have no way of consuming water as the root zone has not formed therefore capillary action is non-existent, by raising the humidity for this phase the wet air allows the plants to consume the excess water vapor via is leaves.
Vegetating/growth: 58-65%
Vegetating plants grow fast in the right conditions, so having the perfect humidity in the growth phase is very important. As the plants size increases through the consumption of water and nutrients, the humidity will naturally rise as the plant transpires water vapor out of the top of its leaves to cool itself down.
Flowering/bloom: 48-55%
As we transition our plants into the flowering/fruiting phase of their life cycle, our (RH) relative humidity needs to drop, if we do not lower the humidity for this phase your plants resilience would truly be tested. High humidity in flower almost always results in powdery mildew, black spot mould, insect infestations (Spider mites love moist air) and the worst mould of all, botrytis.
Drying: 47-55%
This particular phase is just as important as the rest, and some would say the most important phase. By keeping the air quality dry during this phase, the flowers ‘slow’ dry, which improves flavor, yield and appearance. If the humidity is too high, mould will form on your drying flowers and they will end up in the bin. The drying should always be done in complete darkness as light degrades the essential oils that you have worked so hard in forming.
Curing/storing: 55-62%
Once you are this stage, a majority of the major concerns with things like mould are not an issue as long as we store the flowers properly! There are many ways gardeners do this, using glass jars or stainless steel vaults. There are many innovations in the industry to help with stage, Integra have developed a 2-way humidity patch, that maintains between 55-62%, add these to your cart as they will also rejuvenate old crispy flowers and they are quite inexpensive.
So, there you have it.
Excessive humidity for long periods will create undesirable conditions that are perfect for grey mould. Grey mould, once started, will quickly spread and affect your entire crop.
Using a hygrometer device mounted on the wall inside your hydroponic grow room will let you know at a quick glance what your humidity levels are.
It is important to keep nutrient reservoirs covered at all times so that they do not contribute to higher humidity levels.
Humidity levels can be easily controlled as with temperature by using exhaust fans to rid the room of excess heat or humidity accumulation.
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