I have used an ultrasonic humidifier (Air Innovations MH-513) in a small tent to increase humidity along with proper VPD ranges.
What I can tell you is:
I was steadfast in keeping near perfect conditions and got the best looking plants in veg I have ever grown.
My humidity runs below 20% often, (usual mid 30%) so I felt the time/effort and expense was warranted to keep the plants in the zone.
I was so wrong- even though my plants looked fantastic in veg- the actual yield and quality showed no change for all my work.
When you grow in low humidity- the pattern/timeline may be different, but I have found once the roots develope the plant will catchup by flowering time and thrive.
Low Humidity should be at the bottom of your improvement list!
Here is a complete grow in low humidity/low lights etc:
https://forum.growweedeasy.com/foru...s-grow-fastbuds-girl-scout-cookies-autoflower
"Low humidity did not seem to effect the overall grow-may have changed/delayed the usual growth pattern.
I suspect the increased transpiration from low humidity helped provide "catch-up" once the root system fully developed."
High Humidity however, is a different story.