First Grow-Humidity...How Low is Too Low?

[Insight]

Greetings all..I've been reading this site for the last month and decided to try my first grow.

My setup: 4x4x80" grow tent..Phresh 6" carbon filter, Can Max 6" inline fan, air cooled reflector, 600 watt MH and HPS bulbs.
I'm growing in coco/perlite 70/30 mix, in three 5 gallon smart pots. I'm using Nebula's guide as my bible.

I've got 3 seedlings going, two feminized northern lights (not auto) and 1 mystery seed, started in Rapid Rooters. I've moved the seedlings into the smart pots
and have been very careful to follow the instructions on GWE for growing in a large pot. They have been in there since this Monday..4 days.

I've got the 600 watt MH on 18/6 about 30" above seedlings. The temperature at the seedlings with the lights and fan on averages between 75-81° F.
The RH varies between 27-35% but can sometimes dips to 21%. I've got 2 buckets of water in the tent and tried a wet towel to up the RH.

My question is...how low a RH is too low? I was wondering if I needed a small humidifier but don't want to create a mold issue. I thought as the plants grew and I started watering, it may rise. Also, I'm in the NE usa and winter is coming to an end, and so is the heating season...it's when the hot air heat comes on that the RH drops low. I have 2 of the 3 tent air intakes closed.

I'd appreciate your thoughts.

 

[OlldDude]

Hey Drbabe, I'm also on my first grow, however I had an low humidity problem early as well. I just used a small humidifier. I only brought the humidity to 40%. The way I understand things, if you start a seed in low humidity conditions, they will adapt. As plant size increases, humidity will also increase. By the time I switched to flower mode, I had to buy an expensive dehumidifier. You really can't go cheap here, they cost about $200 for a good one. You should buy the best one you can afford. I sure didn't want to buy more equipment after getting my room setup the way I wanted. I just keep telling myself that the second grow will cheap!! That's my two cents worth.
Hopefully someone with more experience will chime in cause I'm no expert......yet

 

[Weed Pharma]

Welcome- I have the same environmental growing conditions and humidity is never optimal- it is however great for not having problems!

I did purchase a small humidifier which I can run while the lights are on.
It stablized my humidity in the upper 30% range- and within a week I had white powdery mildew in one corner of the tent.
I defoliated, increased airflow and all is well.

Humidity is very low on the list for me as I have had many successful grows in the range you mention.

One downside to running low humidity is that your plants will drink more to compensate- so you have to be careful with nutrients as this uptake increases nutrient levels.

You may want to consider putting the exhaust fan on a timer and cycle it off/on to increase humidity.

During the summer months the humidity increases and I have decided to just veg during July/August this year with photoperiod plants.

 

[Insight]

Thanks for the info so far.
It only drops to low 20's% when my hot air heat is on. I'll keep an eye on things as we go. In the summer, I run a dehumidifier in the basement (same place as my grow room and tent) and I struggle to keep the RH at 55%, so I think I'll live with the current RH and maybe lower the heat to the house or close off a vent in the basement until I turn on the air conditioner.

Right now I'm at day 4 seedlings...they are about 3" long with only the first two real (serrated) leaves and the coco is looking and feeling dry.

Another question about watering....They are in the 5 gallon coco pots already..I'm watering in a 2" circle per the directions here on GWE..it says to water until 20% runoff....in a 5 gallon smart pot that could take almost 1 gallon. Should I water that much at Seedling stage?