1st grow in Seattle, with tent, 78°, 71 RH (with fan)

Hi - I'm a rank amateur mid-way thru my first grow: one potted (5 gal) Ak-47 inside a 48" x 48"x79" grow tent. One light in the tent, a single Sun System® HPS 150 on a 12/12 timer, and an oscillating fan on "low". The plant is about 6' and in it's 2nd week of flowering and appears quite healthy.

Inside the tent, the native temp is running around 78° with a 98 RH (this is zipped shut, LIGHTS ON). Ouch. To help cut the humidity during the daylight hours (GROW LIGHT ON) , I am currently unzipping the tent flap about a foot wide, which brings the temp down to about 70° and also lowers the humidity, but only to 71 RH (I close the gap when the grow light switches off at 6).

More factoids: The tent is in the 2nd story of my home (which stays warm in the evenings). The grow light turns on @ 6am, then off again @ 6pm. Inside, the tent temp in the evenings stays within acceptable limits (zipped shut, GROW LIGHT OFF). The deal is, without unzipping the tent and venting by hand each day the RH would still be unbearably high. I know this is an issue many growers struggle with and easy answers seem very elusive...

I believe I've covered the basics facts on this little venture - yes?

So, any tips on how I can best control that RH situation (and ideally the temp as well) inside the tent without doing the manual venting everyday? Naturally, a best solution "on the cheap" would also be great.

Thanks everyone!

Wow, that humidity is rather high! The only thing I can recommend is to get a dehumidifier if you can. They are pretty pricey, but here is one for cheap (comparably). It's about $70 at Best Buy...just an example.

Hey man, first if you can't vent the moisture out like make a hole somewhere then you're gonna have to lower it another way. Don't put so much water in.
Water them little and often. High temps is good in some respects but high humidity = risk of bud rot.

Thanks much for both of these tips. I will try the "less-water" approach next and report back.

Q: Should that single HPS 150 enough for a grow tent that size?

Hmmm...you are working with 16 square feet, so an HPS 150 is putting off about 9.75 watts per square feet, if you take into account the square dimensions of the tent.

How close is the light to your plant? It's kind of hard to give any input on if that's enough light, because the light could be getting lost, bouncing around the tent and not hitting your plant; or a decent amount could be hitting the plant. It's hard to tell without seeing a picture. Does the light have a reflector on it?

I typically like to have at least 50 watts per square foot, at LEAST. But that's using CFL grow hoods, not HPS.

Lighting has been a challenge figuring out for me -- I bought a 24" fluorescent T5 for vegging the clones (works great), but the HPS150 in the tent does seem to be too little (I keep it fairly close to the tops and move it higher as it grows. Are there any suitable bulbs or units that you'd judge as being best for this size tent? If so, would they be an Amazon-available item?

thanks so much for the advice. It really is priceless wIth this kind of operation.

I run 1000 watts no problem in a 5x5. If you can air cool it as well should be no problem. At least a 600. 150 is not enough at all

6' tall and 150w, wow, is it really stretchy?

For humidity I've thought about using the things that they use in shipping containers to absorb moisture in the air, they are relatively cheap and can be ordered online, I'm not sure how effective they would be at that high of a level, but worth a try if you don't want to buy a dehumidifier.

Hey thanks! Yes, VERY stretchy -- another anomaly I have no experience with (?). How does one "top" the plant to hold back height?

Here's an alternate lighting deal i found on Amazon: http://www.amazon.com/iPower-GLSETX600DHMWING20-600-Watt-Digital-Dimmable/dp/B005DOS0R8/ref=sr_1_1?ie=UTF8&qid=1399642401&sr=8-1&keywords=iPower+HPS/MH+Digital+Dimmable+Grow+Light+System

Any opinions as to brand and size? Thanks again all!

I haven't seen that brand but looks the same as the grow lush brand we have here in Oz, I would stay away from cheap stuff like that, they have a tendency to fail and warranty is always an issue.

I use Solis Tek ballasts lamps, fantastic quality but a little bit more expensive. 600 watt would be good but your heat would be more of an issue then.

Check out uncle Ben's topping thread in the advanced section.

I am near Seattle and just harvested, growing in a 5x5 with a 600HPS. My RH was 40-50% up to a week ago so there is something else going on with your environment. Try using less water for sure, and if there is runoff when you water clean it up or put a saucer under it. Minimum for that tent would be a 400 HPS imo, My 600 is minimum for my 5x5...

Good Luck

Thanks for the tip on the Solis Tek -- I'd rather hold off and buy an excellent hardware piece like this - excellent.

I just brought a small de-humidifier into the tent before shutting down the lights earlier -- i'll see how it manages the wetness tonight and again tommorrow with the lights on.

Thanks guys!

You wont be disappointed with solis tek, I'm running 23 of their matrix ballasts and they have never missed a beat, with other brands I've had over heating and overloading issues that just cause headaches.

The dehumidifier is a great idea, now space is going to be your biggest concern, your still early in you flowering cycle, you could try topping now to control height or tying the top of plant all the way down, either way, your gonna have to do something or you might be in trouble.

Yes, thanks again for that. Now, when you say " tying the top of plant all the way down", what exactly do you mean by that?

The plant was severely topped about 4 weeks ago (growing past the light source) and appears to be somewhat in check for the time being... so many variables in this game!

Note: The first morning in the tent with the humidifier offered no results - 95 RH! Today I will install a topside duct fan to (hopefully) suck out the hot air. We'll see how that works...

robnarley1111 said:

Hmmm...you are working with 16 square feet, so an HPS 150 is putting off about 9.75 watts per square feet, if you take into account the square dimensions of the tent.

How close is the light to your plant? It's kind of hard to give any input on if that's enough light, because the light could be getting lost, bouncing around the tent and not hitting your plant; or a decent amount could be hitting the plant. It's hard to tell without seeing a picture. Does the light have a reflector on it?

I typically like to have at least 50 watts per square foot, at LEAST. But that's using CFL grow hoods, not HPS.

Click to expand...

Irrelevant.

Hey Green Town Guy, I am also a Seattle grower and have written many posts about humidity while growing and curing. Although an oscillating fan is a must, you also need ventilation fans to suck the moisture out. When your lights are on, the evaporate the water into your enclosed tent.
I know, "on the cheap" is always preferred for a number of reasons, but it never works out. You get out what you put in.
You can pick up two 6" booster fans at Home Depot for $30 a piece. Put one blowing are in, and one blowing are out.
A dehumidifier would be recommended as well.
It's like this, if you don't get your RH down below at least 60%, you WILL HAVE ROTTEN BUDS.
Trust me, it's happened to me.
Saving money isn't going to mean a damn thing if you whole crop is moldy. To me it would be a waste of money not to fix that very serious problem.

I have a big thing about air flow. It is often over looked in growing because it's not sexy like light and nutrients, but AIR IS JUST AS IMPORTANT TO PHOTOSYNTHESIS.

Don't cheap out on 1/3 of what your plant needs.

Also, rinky-dink home dehumidifier aren't worth a shit. You need one with a tank that's at least a couple of gallons.

Get that RH down brother.

Good luck.

Here's pix of my "maiden voyage" were taken earlier today: a single 5-gal potted AK47, raised from a 5" clone purchased 2/23/14, at 11 weeks total age.

Aha! I've installed an topside exhaust fan and it appears to be working A+ as described - after one hour the RH is already below 60! And this is WITHOUT the additional use of a de-humidifier.

This looks like a win so far -- thanks all!