how well do de-humidifiers work?

[yota]

I cant seem to get my humidity down and im thinking humidity is the cause of my powdery mold issue. Does a humidifier really do the trick? If im around 70% Rh atm, how much can i expect a humidifier to reduce the RH by? and what size would i need for a 4X4 grow space. Would i put the dehumidifier outside the grow space so the air is already adjusted before it is sucked in through holes in the space, or would i want to find a way to have it inside the crowded growspace? Thanks in advance for the tips!

[Al B. Fuct]

I run a typical household type DeLonghi dehumidifier in my flowering room, about $400. Runs 24/7 except in very hot weather when it's not needed. I modified my dehumidifier by removing its tiny 2 litre built-in condensate catch tank and ran a length of hose to a 25L plastic jug. I get about 10L/day of distilled water which I can recycle back into the op or use elsewhere.

 

My flowering room airmass is about 450cu ft; even if the exhaust fans don't run at all, as happens occasionally during cool months with lights off, the dehumidifier will hold the RH to 50% max.

 

The thing stopped my bud mould problem and minimised powdery mildew. I'm still getting some PM as I really pack in the plants in my SoG, but I'm trying to compensate with more, gutsier circ fans to move more air around.

 

Whether you get a dehumidifier or a small aircon unit depends on your avg ambient temps. If you often contend with intake air that exceeds 24-26C, an aircon unit could serve you better as it will double as a dehumidifier in cool weather if run on a humidistat.

 

Since my avg temps are not often above 24-26, in fact I'm often dealing with temps cooler than I want, the dehumidifier works well for me. It adds a bit of heat to the room just sitting there running, which bumps up my lights off temp while reducing RH, both which work against PM.

 

You'll have to find a space within the op airmass for it. You want the thing treating your airmass especially when the exhaust/intake is not running.

[Pam]

My dehumidifier is a big honkin box shaped thing it pulls air in the back and sends the dried air out the front. It would probably work best in line with your vent system. I hope that helps with that...

 

Powdery mildew is a fungal disease. It causes a white or grayish powdery coating on the leaf surface. If you look very close you will see that the coating consists of a network of chains of spores that are easily detached and carried away on air currents. New generations are produced every 4 days!

Unlike most Fungi, spores of powdery mildew DO NOT germinate readily in wet conditions!!!

Frequent washing and wiping therefore reduce the amount of mildew, but you need to be careful. Powdery mildew feeds on the surface cells of the plant not inside so it can be cured.

 

I went and got the book out for ya kid! This shit had me stumped so I looked it up. There's lots of chemicals that will wipe it out, but those are for roses and I wouldn't touch 'em for weed.

I would be misting and wiping, The walls too! It might benefit you to pull everything, and clean the box, I would be putting my plants in the shower and rinsing the stuff down the drain...

Let me know how it goes...

Edited July 27, 2007 by Granny

[Al B. Fuct]

My dehumidifier is a big honkin box shaped thing it pulls air in the back and sends the dried air out the front. It would probably work best in line with your vent system.

 

Don't put a dehumidifier in the duct line.

 

If the dehumidifier is inline in the intake duct, it won't dry the air in the room airmass- it will dry the air being brought in. It will not be able to treat the airmass while the exhaust blower is not running, the function you need most, as this is when humidity will spike up.

[Pam]

I thought the exhaust was running all the time... my bad

 

But having looked up powdery mildew it seems that air moving is what's spreading the stuff.

[Al B. Fuct]

I thought the exhaust was running all the time... my bad

 

A dehumidifier isn't very effective if the exhaust runs constantly. Exhaust blowers should be thermostatically controlled so they kick on at 26C and off at about 25. If the exhaust runs all the time, the room airmass will always be at about the same temp and RH as the intake air, provided there's enough airflow to prevent any heat from lighting to accumulate in the box, with or without a dehumidifier.

 

But having looked up powdery mildew it seems that air moving is what's spreading the stuff.

 

Actually, air motion is one thing which suppresses PM. It doesn't like breezy conditions, low humidity or relatively warm temps during lights off; I try to keep my op from dipping below 20C during lights off. My dehumidifier puts out a little bit of heat, warming the room up a little, especially nice during lights-off in cooler months.

 

There should be an oscillating circ fan in every corner of anything bigger than a wardrobe grow. Small grows might get away with one or two small oscillating circ fans. Every leaf in the op should flutter with each pass of the osc fan.

[Pam]

>Powdery mildew is a fungal disease. It causes a white or grayish powdery coating on the leaf surface. If you look very close you will see that the coating consists of a network of chains of spores that are easily detached and carried away on air currents. New generations are produced every 4 days!

Unlike most Fungi, spores of powdery mildew DO NOT germinate readily in wet conditions!!!<And:

 

Powdery mildew

The most common disease affecting pumpkins in

inland areas is powdery mildew (Oidium sp.). Powdery

mildew generally does not require moist conditions to

establish and grow, and normally does well under

warm conditions; thus they are more prevalent than

many other leaf-infecting diseases in the dry summer

conditions of inland NSW.

 

Well I guess the book was wrong....I'm going to have to write a letter to Rodale press about this! Hmmmm.

Edited July 28, 2007 by Granny

[Al B. Fuct]

Of course, air motion will move spores around. Your mission, should you decide to accept it, is to provide conditions which won't let it take hold and grow easily.

 

Lots of air motion, relatively warm 'nights' and low humidity will prevent PM from flourishing. A guaranteed recipe for PM is cool nights, greater than 70% RH and still air.

[Pam]

 

 

 

Maybe..... we're talking about a different powdery mildew...that's gotta be it!

Edited July 28, 2007 by Granny

[Al B. Fuct]

I'm talking about the usual powdery mildew.