Turning on a mister once a day isn't exactly control. On different days you will get different results. One approach can be to determine a time to run your mister daily and add a humidistat to control a vent fan to pull out humidity over a certain target percentage.

Generally, in warm weather, humidity is a detriment to a greenhouse. Plants can't breathe as well. There is not as much heat transfer available.
The exception is in rooting where you want to limit transpiration.

Thanks for the replies, the primary purpous for our greenhouse is for getting plants going by the time it is warm out the plants are under shade cloth or in ground.

Just something I am wondering about. Theoretically if it is cool weather, fine mists could keep the temperature a little lower than if you didn't use them plus sprinkle dew on everything. At lower temperature, the air holds even less water. I'm thinking you are really looking for the warm temperatures which hold more water in the air, water which gets picked up from the whole ground area. So cool + mist if I did it would just give microbes an easier time to get going on my leaves.

In the supermarket, it is cold, but there is an air conditioner going plus a chiller (another air conditioner) in the veggies section. So misters are good in cool supermarkets because the air is getting dehumidified by both airconditioners, and the veggies dry out quickly in the arid air. So they use misters to put the humidity back into the dried conditioned air. That's the only use I can think of for cool misting of plants asid for living in a cold desert.

In the greenhouse is the growing medium getting dried out? That is what I would look at, and if it weren't I'd guess the first paragraph I wrote applies. I have no experience, only bad experiences with unhealthy condensate too long on my leaves in the mornings. If you don't worry about condensate, but do worry about drying drying, then I guess you have the second paragraph.

This post was edited by PupillaCharites on Fri, Mar 14, 14 at 3:01

It is very common in the propagation industry to increase humidity for cuttings. the idea being you keep the humidity so high the plants have zero or minimal transpiration until they set roots. Otherwise drying out will frequently kill the cuttings. cutting the leaves very small on stem cuttings is for the same reason; to limit transpiration.

That make good sense in that there are no roots to absorb and pump up nutrient water through the stem, so doing as grizz describes is a special application: forcing cuttings to put out roots before anything else, easily cannibalizing whatever nutrients are already in their tissue to do it.

I guess I'm still thinking misting could be more detrimental for healthy seedlings since limiting transpiration for them is going to slow their uptake of nutrients as well as their ability to grow from photosynthesis. For seedlings, once the seed is getting spent, balanced growth with new leaves to begin photosynthesis seems like the priority, they have roots already, and limiting transpiration will set that back and give mold an in.

Though if the growing medium is drying out then mist for sure on the timer, since the mist won't stick around. But it would still be safer with a switch that didn't mist on cloudy/rainy days.

Ok. Makes sense.
Leaves more money for greenhouse improvements

Hey Rio, just a quick weekend note, today I was looking for something fun to do LOL I ended up unannounced visiting a small farm I'd heard about within our metro area. They are getting into tilapia aquaponics now and told me if I wanted to give them a hand and learn together (maybe!), and I thought of you and your Dad.

Showed me their high hoop house, exclusively for starts, and packed really full. Nothing fancy, a couple of portable space heaters they picked up at garage sales for cold nights like $10 each, but what caught my eye was their home made overhead "misting" system. I just figured I'd ask them about it since you were thinking along these lines. I was just an irrigation hose (I don't know for sure but it was like 1/2" eyeballing it) with what looked to me like economical EZ mister heads stuck into it a regular intervals. The upshot of it is, they aren't using it at all, because that design simply doesn't water the starting trays uniformly and this causes trouble. I know you were talking about humidity, but I figured it was related enough...

They were also trying out some more expensive real brass misting heads, the kind that probably cost $10 ea and do well around 60 psi, but the problem interestingly still seemed somewhat to be the same difficulty of uneven watering. I don't know what to make of it, but it was worth mentioning to you. I'm sure better systems are out there but this was a nice DIY job Like might have done, trying to save, but you get what you pay for I guess. Anyway it was a pretty exciting day for me to walk around this stuff.

EDIT: Oops, the cheap ones I meant are called EZ-clone, a few cents each, not EZ mister, those are different.

This post was edited by PupillaCharites on Mon, Mar 17, 14 at 1:34

Thanks for thinking about us. Dad is back in hospital this morning for another surgery. He made the comment on the way here we needed to get this thing put together ASAP.

That's a great oppritunity. R&D on an actual system using someone else's money PRICELESS!

I do know the cheaper misters are VERY pressure sensitive. I had to install a pressure regulator as well as reducing the pipe size on the run to keep the pressure up. For our mist system under the shade cloth last year.