I apologize for the confusion CW. The figures I gave are primarily for greenhouse growing which is what’s happening here in California in a big way. In our experience, most greenhouse crops do best between 60-80% RH although ideal is dependent on crop, stage of crop and temperature.

One of the ways we steer plant growth in greenhouses is by controlling transpiration rates. When temps are very high and RH is low, plants transpire more to keep cool which means less growth… by increasing RH, we slow transpiration down to avoid wilt and increase nutrient uptake. Same is true when temps are low, transpiration slows down, we decrease the RH to increase transpiration rates. As a rule, the higher the temp, the higher we want to keep the RH, the lower the temp, the lower the RH. Make sense?

Indoors, if your plants are doing well between 40-60% RH, then by all means keep it there. (curious what your temp is). There are a pocket of veteran indoor growers who swear by 85F, 80% RH. Others with CO2 injection say, 75F, 70% RH. While other veterans say 60-75% during veg and 40-55% for flowering. What works well for one, does not for another.

Ultimately it’s about what works best for your situation. It’s good to know however, how RH and temperature affect transpiration so you can adjust if you determine that transpiration is not optimum.

>With this Humidity parameters plants will be prone to get Powdery Mildew,how do you prevent it?


POSTED BY FRANDITH GIMENZ

Frandith: The Powdery Mildew fungi likes humidity between 40-100%, warm and shady, high humidity is not the only cause of PM. PM can grow on dry dead leaves if the other conditions are right. Best practice is to create a hostile environment for PM fungi colonizing on your plants:
1. Give plants plenty of room for air circulation,
2. Keep a clean room, pull out any dead or dying leaf material,
3. Don’t crowd or overlap plant canopy,
4. Give even exposure to light,
5. Make sure leaves are fluttered gently by oscillating fans,
6. Drop ambient RH at least 10-20% to interrupt their colonization until you get a handle on it.

If it gets out of hand, Sulfur sprays can be used to suppress established PM or spray potent compost teas high in beneficial fungi on the leaf surfaces only in the mornings so they can dry out before night. Use tea to out compete the PM fungi. If there’s no room on the leaves, they can’t colonize. Once you have a handle on it, keep up best grow room practices to prevent it from colonizing again.

example :As a rule, at 75°F (24°C), if RH is below 60% you must add moisture to get to 75% (which is ideal), but stay below 85% to avoid stress and disease. At 85°F (29°C), if RH is below 70% you must add moisture to get to 80% (which is ideal), but stay below 90% to avoid stress and disease. As temperature rises, air holds less moisture. Steer your plants within these parameters for optimum plant performance.

Is this correct?

Like i said , it contradicts everything ive ever read. Its been common knowledge that 40-60% humidity in an enclosed growrooms is the norm, even with co2 suplementation.

Can someone please explain before thousands of indoor growers crank up the humidity and put there plants in jeopardy.

CW

Keep up the good work!