To find out your local norms for humidity, you could contact the nearest college, or just check the wx section of the newspaper.

Or
http://www.wunderground.com

The closest I could find was for Penn Yan, New York

http://www.wunderground.com/history/airport/KPEO/2006/1/1/CustomHistory.html?dayend=24&monthend=9&yearend=2006&req_city=NA&req_state=NA&req_statename=NA

Just From a Quick glance, it looks like you average about 75% humidity

Here is a link that might be useful: Pan Yan WX

Canandaigua Lake, Canandaigua, NY
http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KNYCANAN3&day=26&year=2006&month=9&graphspan=year

Bristol Hills, Canandaigua, NY
http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KNYCANAN2&day=26&year=2006&month=9&graphspan=year

Here is a link that might be useful: Bristol Hills, Canandaigua, NY

mollyd - usually when a question is ignored it is because the question is either poorly asked or the answer is unknown. Unanswered is a better than incorrect.

If you need information from a successful greenhouse operator/hybridizer/grower regarding daylilies, try contacting Karol Emmerich, Springwood Garden in Minnesota. Greenhouse operation in her area would be appropriate for your conditions whereas answers from a southern grower/hybridizer would be totally different since their gh issues would be cooling, not heating.

And yes, some daylily growers/hybridizers believe you throw a seed in the ground and wait. To each his own or different strokes for different folks. It's also not nice to belittle people just because they couldn't supply YOU with the answers YOU were seeking when you were seeking them.

Brooke

I don't think Molly is belittling anyone. I think that either GH humidity requirements for daylilies aren't known or that daylilies are humidity insensitive and that it just won't matter that much.

Molly, I would add that humidity is harder to control than light and temperature. My GH relative humidity this summer would swing from 39% to 95%, and the fogger and mister had little effect. In the winter, the humidity is much more steady in 50-70% range, regardless.

The standard advice for optimum humidity for plants is around 1kPa below saturated. Clearly this depends strongly, and non-linearly on temperature, which means that you are best off using a computer to control this.

Brook I have no idea what you are referring to when you say I'm belittling people for not answering me.You are not privy to the private email messages that I received so you can not make a sweeping statement that I am belittling anyone.I have named no one and if you feel the need to defend yourself then you have a problem, not me.
Everyone is entitled to do things as they see fit. They are not entitled to dictate to me how I should do them.
As to a poorly written question I don't think asking if anyone knew where I could find humidity charts constitutes a difficult or vague question. Please keep your opinions to yourself and don't bother reading my post if you find them so offensive.

MollyD

Nathan has made his usual quantum cognitive leap and put understanding of the humidity issue beyond the reach of most of us. The advice is almost certainly technically accurate but not practically useful for most of us. :-)

Nathan, would you mind restating the "standard advice" in another way? Maybe make a suggestion within the reach of a GH hobbyist?

You know, one reason I don't visit this site very often any more is because of the frequently rude and sometimes even hateful people on here! Poor Molly is trying to get some information, and instead of replying with "I'm sorry you have had so much trouble getting your question answered. My experience with humidity levels in the greenhouse for daylilies is...." she gets berated for stating the problems she has encountered in trying to find the answers she needs. You'd think she'd actually accused this site's members of being the ones that "ignored or derided" her (which wouldn't surprise me).

What happened to the nice people that loved to assist people in finding the answers to their gardening questions? Why can't things return to the nice, helpful way in which this site and many others originated?
Gail (who likes sites with nice, helpful people!)

Stressbaby:

Don't worry too much about it; it's not that important.

Basically, the hotter it is, the more moisture the air can soak up. Thus, 90F air at 100% humidity can hold much more moisture in it than 40F air at 100% humidity. What Nathan was saying (which is interesting, by the way) is that plants like to have less humidity (1kPa less; 1kPa is about 0.9% of the air's total pressure at sea level) than how much there would be if the air was holding all of the moisture that it could.

What "percentage" humidity this will be, thus, depends on what temperature the air is, since that maximum amount of moisture that the air can hold is dependent on temperature. This means that the colder it is, the lower the percent humidity you want.

OK, I must have missed something somewhere.
Yes I am a southern Gardener, But I am not Ethnocentric, so I would not assume to give weather info from the south to someone in the North.

So, when MollyD asked;
"I suspect that something that mimics the norm in my area would work but I have no idea what that is or how to find out what it is"

I Provided Links to Data from weather stations in her area for the past year so that she could find out what the Normal HUmidity in her area was...

Jimmydo, I think Gardengail is referring to Brooke/highjack. Don't worry about it, keep posting. Aside from Brooke/highjack, this is just a healthy exchange of ideas and information.

Karenrei, I totally get the temp/humidity/dewpoint thing. My point for Nathan is this: who measures humidity in kPa? Hardly anybody. Maybe nobody. Most of us have a little meter which gives us relative humidity. With temperature swings and the associated swings in moisture capacity of the air, how would you maintain a particular humidity level 1kPa below saturated? Practically speaking, if I wanted to do it (and I really don't until I see a reference), how would I do it?

SB

That's the problem, SB. There's no single percentage that works. You either have to understand the concept of partial pressures of water (kPa), or use a chart.

Here's a table, if that would help:

http://ohioline.osu.edu/aex-fact/0804.html

At 100F, you're looking at about 90% humidity. At 45F, you're looking at 0% humidity.

Karen is spot on in the explanation.

stressbaby: It doesn't matter whether you and the rest of humanity measure humidity in relative terms, plants seem to like humidity measure in absolute terms. How would you do it? Buy a computer than controls the humidity. The term in industry is 'VPD' - vapour pressure deficit. How would you control the humidity in relative terms anyway?

Saturation is fairly easy to obtain, perhaps you then mix 1% dry air in with the saturated air. I'm sure there are ways to approximate it.

Now I am convinced that neither of you understands my points.

I totally get the concepts of VPD, relative humidity, dew points, vapor pressures. The link is great, though, thanks, I've saved it to GH favorites.

I'm making a couple of points. First I'd like Nathan to reference his statement that "the standard advice for optimum humidity for plants is around 1kPa below saturated." This is a VPD of 1kPa. Now, I have been gardening for many years and I cannot recall ever reading such a statement. The link above indicates that it is best to keep the GH above a VPD of 0.2-0.43kPa to prevent disease...and that's a start...but this is not what Nathan said. Educate us, show us data! I'm up for learning something!

Second, we don't measure the vapor pressure directly. We can calculate it from a chart using RH and temp. While the idea of VPD is useful, how can a GH hobbyist make use of the science? I can measure RH and temp, but then I've got to go and calculate the VPD. Is there software that does this? Is it available at a reasonable price to a hobbyist?

Third, Nathan said I can "use a computer to control this." It is easy to say "buy a computer." But that information is just not that helpful to me. Software? Then what? Misters? Foggers? An average summer day this year in my GH had a temp of 95F and afternoon RH of 40%...this gives me a VPD of around 3.3kPa (correct me if I did the calculation wrong). Nathan, practically speaking, how do you propose I get the VPD to 1kPa?

I'm just trying to learn something and to make the science accessible and useful to everybody.

Thanks in advance. Sorry for the threadjack, Molly.

SB

Well... I don't know what pre-made computer controls exist, but it wouldn't be too hard to program such controls. I picture something like this:

1) A temperature/humidity probe with an readout that is sent via radio or other means.
2) A computer that can read the results in a way that a script could extract them.
3) A humidifier
4) An X10 device (or similar) hooked up to the humidifier
5) A computer X10 controller
6) A python script that polls the humidity every 30 seconds or so. It compares the temperature and humidity to a table, and if it's too moist, turns on the humidifier. This would be very easy to write if there's an easy way to get the humidity/temperature data to the script.

the figure of 1 is easy to remember. I think the optimum range is 0.8 to 1.2 or something. I am still thinking there is an easy way involving a thermostat, a vent and a swamp cooler. take air from within the greenhouse, humidify to 100%, mix in outside air proportional to temperature. It will be a first order linear approximation, but it might be enough over a reasonable growing range. You might approximate the values below 15C as 0% RH. This could be done with say temperature controlled vents, fans thermostats and some basic maths.