JB,
I think what is more important is trying to maintain a constant high/low temp no matter what that temp is. This does depend on what you are growing or maintaining of course. Extremes between high and low temps can result in internodal stretching. What I'll bet is most folks with hobby or smaller g/h's don't have any issue maintaining a low temp in the winter but they do have an issue with the g/h getting to hot.

Most folks don't or won't make the investment (including me till next year) on any cooling except for a shade cloth, exhaust and vents. Both of which in most cases will not hold the temp down to a reasonable limit during the height of day time sun. You are correct, even in the winter your G/H is going to get hot. I guess if one was home all day they could run out and put on the shade cloth then take it back off every day. That's only practical if your home and you have a rather small g/h. It would not work in our case. Sure shows the importance of having the correctly sized equipment.
Our solution is evaporated cooling. This will help maintain a much more steady temp between high and lows.

Just for fun here's our numbers:
G/H 1 heat 58 Vents Gravity Exhaust 65
G/H 2 heat 52 Vents 60 Exhaust 65
G/H 3 heat 42 Vents 60 Exhaust 65
Cold frame Vents 35 Exhaust 40

Thanks Mylu. Everyone is going to be a bit different I suppose. What do you grow in those different houses that determines the range you shoot for?

jb

G/H 1 Propagation house and seed starts. Also the smallest house and double wall poly so it's the cheapest to keep warm.

G/H 2 Perennials (growing on after g/h one) We grow to many varieties to keep every plant in it's ideal grow on range so we compromise on temp. They don't seem to mind.

G/H 3 Annuals from March on only (Only heat with kerosene on nights forecasted to go below 40)

Cold Frame Over wintering perennials and trees/shrubs

Heat 54
Ridge vent ~75
Intake shutters ~80
Fan ~84
Mist 90

Exhaust fans at 65F would be running 24/7 at times around here.

SB

Exhasut fan 86*
Heat 58-62*

Exhaust at 65?! Why do you exhaust at such a low temp. Most plants really like it more in the 65-75* range.

exhaust fan is set for 84 degrees.heater set for 50F.

Weebus you answered your own question. We try to maintain a constant temp in the greenhouses. We do not want the temp to swing from 55 at night to 85 or 90 in the day.
Our goal is 55 at night and no more then 70 in the day. 15 degree swing not a 45 degree swing. That kind of swing helps induce internodal stretching. We want compact plants not stretchy one. We do not spray with b-nine. ". 80 degrees and up is way to high for a grow on temp. Even 75 is to high to grow on.

The house will heat up more then 65 degrees with the exhaust running. So by setting the vents to 65 we might hit 75 for a high which is right were you said "most plants like temps between 65 and 75. BTW we don't grow tropical plants.

Are these winter settings? Summer settings? All year round. And what Zone are we talking?

I could see the 65 degree exhaust running most of the day, but in the PNW zone 8, even in summer it wouldn't run all night.

Thanks,
jb

We try to maintain a constant temp in the greenhouses. We do not want the temp to swing from 55 at night to 85 or 90 in the day.
Our goal is 55 at night and no more then 70 in the day. 15 degree swing not a 45 degree swing. Then I would raise my night time temps instead of keeping my daytime temps so low. We keep the GH at work at a 65* minimum because we too realize that we don't want our native (note Non-tropical) plants to stretch. That kind of swing helps induce internodal stretching. We want compact plants not stretchy one. Oh, Really. We do not spray with b-nine. ". 80 degrees and up is way to high for a grow on temp. Even 75 is to high to grow on. Absolutely not true. I have no idea why you would think that since there are mountains of research stating otherwise, well unless your are growing ice cubes, then I defer...To say that 75* is too high to grow on is like stating that plants don't grow in the late spring early summer. If I am not mistaken, that is the most active growth period for plant's foliage.

Do you have some type of documentation about that? I mean, that statement, from a grower just blows me away.

JB theyÂre all year. Well most of the year. We shut down all the houses by June 30th. All the plants are outside at that point. We fire up the propagation house November 1st and the perennial house by mid January.
We're Zone 6a. No the exhaust will not run all night in the spring but come May it might, June for sure.
Yes on some days the exhaust will run all day. Fresh air is good.
This morning it was zero degrees outside at 7am with clear skyÂs. Zero in the perennial house. I called the temp alarm at 9am the perennial house was already 50, outside 9 degrees. 10:30 am 13 outside 67 inside. As you can see weÂll reach 80 to 85 today. The point is G/HÂs heat up fast and will over heat fast too hence the lower start temp on the exhaust.
It all depends on the function of the house. We keep the seed house warmer at night to keep from stunting the seedlings from cold temps. We keep the perennial house cooler to help eliminate stretching. These houses are for production not hobby. Well thereÂs a little hobby in it :)

Mylu, I have a hobby house at home, which is what I usually speak of here, so that I don't confuse people. When they ask questions, I try to answer with information they can use, not what I would do with a commercial house.

When I reply to you, it is on the commercial growers level since I know you grow commercially. Keeping your GH cooler doesn't necessarily keep your plants from stretching, it is the temp swings that make them stretch. I still say, keep your night time temp warmer, put in an exhaust system that can handle your house, and you would see a marked improvement in your perennials.

My two cents. I am, like you, afraid if someone sees on GW keeping a house at 65* for growing, that they will live by it, not knowing any better...

I didn't say keeping the g/h cooler will keep the plants from stretching. I said eliminating large temp swings will help. Which you agreed. I unlike you do not live in the PNW zone 8. If I did then I too would heat more in the winter. I'll move the temp up to 65 at night. Now where did you want me to send the extra heating bill?

Our data comes from our seed supplierÂs cultural guide. My guess is since they have been in business since 1879 it is they're data they use. Most grow on temps do not exceed 75 degrees for our varieties, quite a bit are from 60 to 65. Many from 55 to 60. I'll be happy to mail you a copy.

Here's one example: Notice the grow on temp. Now why would I want my g/h above 75?
Platycodon (balloon flower)

Products:
Miss Tilly NEW ADD!
Unique container or front of garden highlight.

CULTURE:

GERMINATION REQUIREMENTS
Germ Temp: 60-70° F
L/D Req: L
Days to Germ: 8-15

GROWING ON TEMP: 55-60° F
The external environment you grow in is by far different from mine. It can get to 10 or 15 below and well over 100 in the summer. Last year we had high temp of 70 in February and it still frost in May. It was a wacky year.

As I stated we grow about 130 different perennials in one g/h. We can't (although I wish I could) meet the correct grow on temps for every variety. We have to compromise. As you said in the past "when we get bigger" we can address this issue. Any who our plants look great on May 1st (our target date) and that's what our customers like.

These discussion are great for folks that are learning (which I still am) or wanting to get into the business.
I just don't get why folks have such a hard time with my method is different from thereÂs or yours is different from someone elseÂs. They're both right for each situation.

Weebus, Sorry I missed one of your points. You do realize I'm talking "grow on temps" right? the temp you should grow a plant after transplanting (from seed prop tray) to finished product during it's 1st year?
Just making sure were on the same page.

I just don't get why folks have such a hard time with my method is different from thereÂs or yours is different from someone elseÂs. They're both right for each situation.

Science types of discussions are difficult over the internet, because ther isn't any warm and fuzzy to it. Being pushed in an academic sense is good. We all learn from it. I get frustrated when others question my methods, but it makes me stand back and look at what I do and why. Somethines I see that I do things "Because I've always done it that way." Huh?

Don't get frustrated that your way is different and you are being questioned, ask Dax, he learned a TON with us pushing on him the whole way. I learned a lot from him. We (I)just have to remember not to push too hard.

I learned that my 3 foot high Coleus that I am famous for in this area is because I was letting the day time temps get way above 90F so I could store enough heat to get me a 32F at night.

I thought it was the lack of light at high temps that was causing it but after being told it was the difference in temp that caused internodal stretching on here I did some other reading.

An interesting point is that.... as seedlings if a coleus is exposed to that internodal stretching it never recovers.

It continues to grow with the same leaf spacing even when transplanted outdoors, no matter how hard you prune it.

Chris Even heating to 90 doesn't your temps drop below 32 anyway?

Hey Weebus you do tend to get pushy... hehehe. BTW our g/h are designed by Atlas so I kind of think our venting is adequate.

Chris, do you use fertilizers? For eons it was thought that N was the culprit for internodal stretching, but recently it has come to light that phosphates are responsible. If you fertilize and use a low high high (NPK) just tuck that in your cap...

Mylu, how do you control botrytis at such low levels of heat?

Chris, I find your coleus story fascinating (where were you two summers ago?) when I had really bizzare internodal stretching on my coleus (rainbow mix from seed). Okay, let me get this streight....the stretching occuring at the grow on stage(due to temp swings) CANNOT be recovered once planted out? Is this correct for all/some/almost all plants, or just for Coleus???

THIS IS VERY GOOD INFORMATION, if you all would care to elaborate more. For instance, when is the danger of this over with? I mean, once I harden off, my plants are exposed to really fluctuating temps before getting planted in May. When exactly does this stretching problem begin/end due to fluctuating temps? The only plant I have ever had get stretchy on me is Coleus.

The greenhouse installer and the company tried to talk me into smaller exhaust fans, mainly because the larger ones I had ordered wouldn't fit without cutting into the greenhouse frame. I got smaller fans but more of them(3 instead of 2) to get extra airflow. They all said it was overkill. Well it wasn't. I knew how hot it got here and had been in enough commercial greenhouses to know more is better.

Mylu, this is a quote from one of Cactusfreak's postings. I tend to believe her also. It shows that these guys don't always know what they are talking about, or directing you properly. So just because Atlas said so, doesn't make me believe them.

Just food for thought...

Mylu, I was/am just using water as a thermal mass to provide heat at night. The warmer you get your water in the day the lower temps at night you can survive with no additional heating. What is new to me, and explains a lot, is the fact the plants are experiencing a temperature differential of 60+F is causing growth problems.

Weebus, Everything gets water soluble 12-12-12 at the rate of 1/4 tablespoon/gallon every 2 weeks. Maybe I should pay more attention to the individual requirements of my plants next spring.

Ellen, Yep!! Rainbow mix from seed. Do it every year.

Last spring noticed that the ones I planted early and put in the greenhouse were leggy. I also planted some seeds later in spring and they also were in the greenhouse but the north roof had blown off by then so they were just sheltered from rain not at a high temp. I expected the "leggy" coleus to be normal when I planted them out, but no!!! they were skinny 3ft high plants all season. The later ones were much more compacted. More like the seed packet picture.

Weebus "reference link for proper credit"
Botrytis blight or gray mold is a fungus disease which infects a wide array of herbaceous annual and perennial plants. There are several species of the fungus Botrytis which can cause blights; the most common is Botrytis cinerea. Botrytis infections are favored by cool, rainy spring and summer weather usually around 15C (60F). Gray mold can be particularly damaging when rainy, drizzly weather continues over several days.

Although IÂm sure you have this memorized but these conditions above do not exist in the houses. We use Netefim auto-drip system to control watering. The surface stays dry and so does the foliage. But I'm sure your aware of that.

The greenhouse company in your example didn't design the system.

Quote "mainly because the larger ones I had ordered wouldn't fit without cutting into the greenhouse frame."
Cactus ordered the fans not the company.

You know as well as I do airflow is a simple calculation of g/h cubic feet to the amount of airflow required. Big or small fans. Doesn't matter as long as the proper airflow is achieved. Sorry to many wholes in your argument. And IÂll trust a g/h engineer any day.

Hey you never did comment on most grow on temps are between 55 and 70?

Chris,

What's the lowest temp you ever recorder? What about days when you have overcast skies for days on end. I can't see the temp hitting 90 in those conditions. Maybe 70 but does that store enough heat? What's the percentage of floor space is used for storing water compared to plant space?
Just curious.

Here is a link that might be useful: Botrytis

The lowest temps are just a couple of degrees above outside temps when the greenhouse is empty.

At GREAT personal risk I just battled my way through snowdrifts and stuck an electronic thermometer in the greenhouse

Left it in there for 15 mins then heroically fought my way back and checked it. Then for scientific accuracy I used the same thermometer to measure the current ambient air temp. The whole process took two beers to accomplish.

Results!!!

Greenhouse 32.9F

Outside 34.7F

Yep, it is COLDER in the greenhouse at 10PM tonight than it is outside. We just went through days of sub freezing daytime temps (one day high was -4) and night lows of as low as -17. On the thermal curve the greenhouse is now lagging behind the ambient. There is no thermal mass in there at the moment except for the cement floor.

As to when I get all my benches and greenhouse in a greenhouse and water in there if the water at the top of the trashcans was 55F or over I didn't worry if the forcast low was over 25F. I knew the plants would be above 33F

As to area. the 300+ gallons of water were under the benches. They were the bench supports. The greenhouse in the greenhouse was 9ft by 11ft inside a 14ft by 24ft.

Total bench space 64sqft or 32 regular flats with 288 cell plug trays = 9216 seedlings.