Ventilation question for a small greenhouse - Orchid Board

samnkyle · #1 11-29-2011, 06:09 PM

Ok, so I have this 4.5' x 4.5' x 6' plastic greenhouse that I got a month or so ago to house my seedlings (catts, dend, rhyn, vandas, etc.) and some mature phals and catts...
It's underneath my patio cover and it gets only about a couple of hours of direct morning sun. I have a small utility heater/fan so the temperature doesn't go lower than 60 degrees at night.
I also just installed a new misting system so it can water the orchids every (other) day when I'm not home. (I live in Orange County - SoCal and I work Mon-Thu in NoCal).

I think I got the humidity issue taken care of with humidity trays... As well as the temperature at night with the heater.. So my question is, is it sufficient to just leave the plastic door unzip both day and night to allow for ventilation or do I continue to unzip in the morning and zip up at night.. or do I need a fan? The heater I got can function as a fan too but it's a manual knob...

Is there a fan/heater with thermostat that can turn on the fan during the day and the heater at night that won't cost an arm and a leg? How about a cheap thermostat for turning on the mister when it gets too hot during the day instead of the timer which is what I have right now? (Please remember, my greenhouse is rather tiny since I'm just starting out... and I live in Southern California, not much inland but about 12-15miles from the coast.)

I've lost a few seedlings already from over watering.. or too much sun exposure before I moved my greenhouse under the patio cover... whatever's left hasn't grown one bit... so any helpful suggestions would be greatly appreciated!

Muchos thank yous in advance!

Zoi2 · #2 11-30-2011, 01:17 AM

I don't grow in a greenhouse so really can't help but am giving you a bump.
Joann

Ray · #3 11-30-2011, 08:36 AM

Your heater could be wired to have the fan on always, and just have the heat cycle on the thermostat, but even with a small greenhouse, you really need to consider 4 things:

1) Heating - done
2) Air movement internally
3) External ventilation
4) Humidity - done.

Merely moving the air around the greenhouse won't help if it gets really hot, but it's still important for disease prevention, and constant external ventilation could conflict with heating, running your costs up.

I suggest the following: a reciprocating fan internally for constant (24/7) air movement, and a louvered exhaust fan on its own thermostat to draw excessively hot air out.

FIT BMX · #4 11-30-2011, 01:32 PM

What kind of greenhouse is it? And what is the framing made of?
A photo would be great, I know more about greenhouses than I do orchids!

samnkyle · #5 11-30-2011, 01:44 PM

It's just a plastic greenhouse.. It's my starter greenhouse..

Ventilation question for a small greenhouse-clear_plastic_greenhouse-jpg

Figured once I'm successful in growing my seedlings, I'll move to the sturdier, polycarbonate of some sort.

So, sounds like I'll need to have a dedicated fan separate from the heater?.... and still have to zip/unzip regularly to allow blow out hot air and let external air in.

Thanks again!

FIT BMX · #6 11-30-2011, 07:05 PM

A greenhouse that small is very hard to control the temp, and humidity. But with some modifications it will work great. A roof vent is one of the best way to control heat, http://www.amazon.com/Cold-Frame-Aut...2695507&sr=1-2 sells a cheap vent lift.

samnkyle · #7 11-30-2011, 08:26 PM

Wow! A vent that automatically opens and closes based on temp, that's cool. I thought those need solar power of some sort. Good to know... Just not sure it'll work for my flimsy plastic greenhouse... Mb when I get the poly... I'll keep that in mind.

Thanks Fit BMX!

Ray · #8 11-30-2011, 09:38 PM

I have "solar" openers on mine- they expand when warm, opening the vents.

samnkyle · #9 12-01-2011, 01:18 AM

Gosh! There's so much to learn!
I'll take a look at your website, Ray.
Thanks!