Hoop House Issue...How to Solve Please!

I put the cover on the HH today. It was a great day to play with the temps inside the thing. Well, observe is more like it. I wanted to know how hot it might get, and how the sun affected things.

Well, we had a great day of varying sunshine. Sometimes, full and intense sun for half an hour. Other times, a high overcast that really screened out the sunshine, but nothing even close to shady/cloudy. Actually, perfect lighting for outdoor photography of animals and buildings, etc......diffused lighting.

My air temp was in the mid to upper 60's today. When the sun was blazing, it got to 97F in the HH. When the sun was diffused by high clouds, it was around 79F. So, quite the variance in temperature. I don't know that I like that. Question 1....are those normal fluctuations?

I also noticed sun angle means a lot, too. During midday, the HH had no problems heating up. After 4pm, though, the temps dropped rapidly. I was outside about an hour ago, and the sun was shining on the HH directly. The air temp was 70F, but the HH temp was only 73F. Question 2...should I be concerned by how quickly this drops off at night...and it's ability to hold steady temps?

It seems it makes no difference if I get to 500 degrees during the day if I'm still going to drop back to 27F at night....in a matter of hours.

Here are some things that "may" help you help me.

- 3.5mm thickness on the plastic covering. I had choices from .7mm to 6mm. I thought about buying the 6 for any help it may provide, but the 3.5mm was just the right size for the dimensions of my garden.

- We had only a 10-15mph breeze today, if that. So, it's not like it was windy. And, I became concerned about air getting in. I shored up some more spots, but it is making me think this thing has to be completely airtight....and that can't be necessary. After all, warm air comes predominantly out the top, right?

Tomorrow, I will check the temps of the air and inside the HH first thing in the morning and compare. I will also fill and add my gallon jugs of water in hopes I get a better differential Friday morning.

I know it's trial and error, but man.

One other thing I realize that may avert some of the panic.......the cover will only need to trap "some" heat after frost dates. And, it can't stop weeklong stretches of subfreezing weather and cloudy days. The cover will keep most of the frost off after the soil temps heat up. Which could also be part of the problem.....the soil just 3 inches down is still really cold. That may help explain the rapid cool off when the sun ducks behind a cloud.

Please help me discuss. As you can tell, when trying something new, I like to nip any potential issues in the bud.....so to speak....lol.

This time of year, as you know, the hoops are going to extend your season by adding warmth to the bed so you can plant a few weeks earlier and the seedling can get a head start. You are well on your way. I am not an expert; I do have a little experience with cold frames in particular, but I will address a few questions.

If it is getting very hot under the hoop, plan on venting somehow.
To retain heat into the dark, colder hours, you will need mass that will absorb heat during the day and slowly release it at night. The water jugs are good. I painted mine black.

I cannot give you all the details in this brief post, but I will encourage you, and anyone else reading this post,to try an internet search on subjects like hoop house, cold frames, hot beds, passive solar, things like that, you will find a lot of your questions answered and plan how to use your hoop to the greatest advantage.
It is a learning curve. But I think my best advice would be don't forget to open the tent on those days you know it is going to be sunny.

Absolutely. Once I saw 82 this morning, I thought.....Well, even on a day like today I need to plan to roll up the sides. 97 was crazy. But, today, I wanted to see how long it could hold that heat.....and was disappointed.

The water will help no doubt. And, so will warmer soil. And, at 97F, that soil ought to warm up quickly enough to get some ambient heat flowing along with water juggies.

I am wondering if I buy thicker plastic....6mm....and double it over.....effectively making it 12mm....if that will slow down heat loss. It should, but each level of thickness will also cut sunlight allowed in.

I'll search. Thanks for the help.

There may be some benefit to thicker film, but an envelope would be better, me thinks.

What do you mean by an envelope Camp?

I would like to know that, too, Jennie.

At any rate, here is what I found with a quick search. http://www.ehow.com/how_7557713_collect-suns-heat-hoop-greenhouse.html

This statement really helped me understand the drop in temperature was to be expected. "At night, hoop houses lose heat rapidly due to lack of insulation."

So, the best approach is to likely put in the water jugs and paint them black.

I have a 24'x14' HH around Nashville TN. I get about a 7degree differential in the coldest nights and am happy with that. I do have a 6mil covering. I would think that anything less than that would be easily damaged. Depending on how large your HH is you may need alot of water to make a difference. I have three 55 gallon drums in mine plus another 400 gallons in my aquaponics system that I heat. On the coldest nights I cover my plants in the greenhouse with another covering called agribon 15 that I get from Johnny's Seeds. With all of this I haven't lost any plants even when it got down to 11. I didn't even use an air heater this winter.

Hope this helps.
Richard

camprn wrote:There may be some benefit to thicker film, but an envelope would be better, me thinks.

In this case I mean 2 layers of film separated by a space, thus creating an envelope. Kind of like double pane window.
something like this

I got the above image from http://thenauhaus.com/blog/index.php/tag/chapter-5/

I've also heard of people buying a clear solar pool cover (the on that looks like bubble rap) and turning it so the bubbles are down and putting it over the top cover. I do agree that to get any benefit from two layers your going to have to put some space between them. The space acts as the insulation.

Richard, thanks a bunch. I originally thought the same thing about 6mm....durability. However, I was told somewhere that the "thickness" didn't make much difference in heat retention, so I went with the 3.5mm.

Mine only measures 4'x12'. So, I don't have a ton of space to heat. However, I'm sure it's going to require more water than I can fathom. I may have to cut the size down since I won't have all 64 squares going right out of the shoot. I just thought it looked better to have the whole bed covered instead of part of it. And, the added expense was so minimal.

Camprn, I was envisioning something else when you said envelope, but that makes sense. One thing I read last night was stating that you need to "trap" the heat. And, multiple layers help do that. I am thinking of a floating row cover that would provide at least one extra layer. Along with that, it would stay in place once I take the plastic off the house. But, we'll see. As with everything, it's a "work in progress."

Sort of stinks, though, I sure thought the HH was a simple concept. But, once again, I've been shocked by reality...lol.

Don't get discouraged. Though we have a greenhouse we also grow a 4'x20' bed outside all winter here under just a row cover. Also we only have one layer on our greenhouse and it does fine. Like I said we do cover those beds as well on really cold nights. As for the thickness we have walnut trees that rain down walnuts 2 1/2" that almost puncture our 6mil. I have used 3mil for row covers and have some of that left that's 3 years old. We are really into "use what you got".

Good luck

VENTILATION ! ie: open the doors , raise the sides , buy fans you can put on thermostats,, I purchase a vent kit from Intlernational greenhouse supply co it had two vent lovers with motors a tstat and a fan all for under 300 bucks works great! but even on a 75 deg day with vents open fan on, the temps still get in the low 90 range , next step is a shade cloth 50%

Jay birds right about the other end of the seasons. I love my greenhouse, but unless you spend more money than I want to I am always in a battle to moderate temps. I have two fans in mine and it does still get too hot on the hottest days of summer. This next year I might get a sun screen. Last year I trained my tomatoes so they offered everything else in the greenhouse shade. As for my fans I used two old roof fans that my Dad replaced an gave me.

I'm a bit confused. BBG are you talking hoop HOUSE or hoops over your individual SFG beds only? :scratch:

Don't forget you want to measure the temperature of your hoop-house at GROUND LEVEL. The temperatures near the plastic cover will fluctuate dramatically while the temperatures near the ground will be much more stable.

Also you might want to check out Eliot Coleman's book: "Four Season Harvest" which clearly explains the use of double layers in hoop houses. He grows vegetables year round in Harborside, ME using UNHEATED hoop-houses in near SFG conditions. It's true that his farm is HUGE compared to most SFG's - but that doesn't mean his ideas can't be adapted to our smaller areas. It's good reading!

Not to take anything away from BBG, but I'm also going to try this myself. My setup is a bit smaller, the frame work is just going to go over one of my beds and only 2' or so above the soil. I have the insulating cloth cover from Harris seeds and I have 3mil plastic. So on sunny days, if I vent the plastic, do I also vent the white cloth?

I'll post pics after I set it up this weekend but if there is a different way I should set it up please let me know.

I've already started saving some milk bottles, since I'm just trying to warm 2' x 6'. I don't know if this small scale is considered more of a "hoop house" or "cold frame". My goal here is to use it to get tomatos outside a few weeks sooner.

Thank you for explaining envelope...that makes total sense.

Camprn....just over the individual 4x12 bed. However, I have read it as a hoop house, so am calling it accordingly. Nothing elaborate for sure.

gloria...i do measure at ground level. thanks for the reminder...and the book recommendation.

Guys, my lack of ventilation currently is ONLY because I don't have veggies in there yet. I am letting it get super hot in there in hopes it will warm the soil deep enough to also draw ambient heat from underneath. If I had veggies in there, no way I would keep it covered in a 60F sunny day. Probably would roll up the sides on a 40F day with sunshine.

I put the juggies in today. And, I measured the soil temps. I didn't take the time to compare to the actual soil outside the beds, but the soil inside, at 6 inches deep, is 46F. Not bad considering just four days ago I was breaking ice clumps as I was mixing my MM.

I'll let everyone know tomorrow, hopefully, how the water did overnight.

I love Eliot Coleman's books, I have both Winter Harvest Handbook and Four Season Harvest. You can see some pictures of his farm at the Four Seasons Farm website.

First night with the milk jugs, and they may work!

Last night, the temperatures inside and outside the hoops were identical. However, this morning, it was 42 outside, but 46 inside. A 4 degree differential I will take!!

If it stays consistent from here out, I am about a week or two from taking my chances with lettuce and spinach.

This is going to sound like a really stupid question but I gotta know. Do you leave the caps on or caps off? I almost failed science in high school so I'm not sure how these principles really work. I'm setting up my hoops today.

A good query. If I have water filled milk jugs I cap them. If I am using milk jugs as cloches I will leave caps off to allow ventilation, unless it's going to be a cold night.

jerzyjen wrote:This is going to sound like a really stupid question but I gotta know. Do you leave the caps on or caps off? I almost failed science in high school so I'm not sure how these principles really work. I'm setting up my hoops today.

I am no scientist, either. But, I cap them when full of water. I am wanting max retention. Uncapping seems to me that it would allow the water to cool faster, which is not what we want.

Same for uncapping cloches. I don't want any ventilation, do I? I am trying to keep the warmest air possible next to the tender plants. Why would I let the heat out? Camprn, please correct me if I'm wrong....before I do it wrong. Like I said, I'm not an expert and am testing a hoophouse for the first time as we speak.

Jen, I will tell you my plans going forward do not yet include cloches. I have about 17 milk jugs inside my 4x12 hoop house. I have used 6mm plastic on top. But, I have saved my 3.5mm plastic (that I used originally this week) for an additional floating row cover inside. Instead of cloches, I will just put the 3.5mm plastic inside and drape it over the jugs. That should sit about a foot off the soil and give the milk jugs a double layer, which I've read really helps things. The more insulative properties you can give your HH, the better off you are when temps really take a dip.

I plan on testing the row cover tonight, and will tell y'all what I see tomorrow morning. Again, though, we are only aiming for a consistent few degrees over air temps with our covers and HH's. If we can keep things from freezing when night temps fall to 28-ish, we are doing well. However, if things drop to 12*, there isn't much we can do consistently without taking more drastic preventative measures.......from what I've read.

The quick update is that I forgot to put the plastic row cover on last night. However, I did run out to Walmart and grab a $6 max/min thermometer for outdoors. Air temps got to 43 last night, HH stayed at 47. Two nights in a row of a 4 degree difference. Hopefully, I get a little more when I get the row cover on tonight.

BBG,

I can feel your frustration. It is a lot more work trying to "cheat" mother nature than I ever anticipated. Trial and error was a phrase I was getting sick of hearing. I'll share my story last fall of my first SFG season and its successful but tiresome extension. I was a little disappointed in just the few degrees of differential I too was getting using 4mil plastic. Some nights there was no difference and at best I got an average of 4-5 degrees. Not enough to get me past the low 20's. Then I went with a blanket draped OVER the top part of the "wagon" and then another layer of plastic to create a dead air space. This gave me another few degrees on SOME nights but was probably negated by the sides of the hoop house (not a strict hoop house but plastic over my SFG's) not having blankets there. Personally I'm not convinced the SFG process can lend itself as well to how Eliot Coleman achieves his differential. I love the books but seeing as he mainly plants directly into ammended soil, his first layer of floating row cover traps the ambient heat of the earth itself. Raised beds are exposed on all sides and so cannot fully take advantage of that process.

I tried using bubble wrap to create the dead air space in between two layers of plastic but that was a total disaster. Pure frustration and gaps everywhere. Drove me NUTS ! In the end, supplemental heat was the only way I was willing to go to be sure I did not lose my crop AND sleep soundly at night ! My whole SFG garden area is also raised on 3 inches of gravel and so I had more heat loss that way plus a detachment from the earths ambient heat. The old style big bulb christmas lights were cost effective and worked perfectly. I was now easily up in the 10-12 degrees range with one layer of plastic. Here in upstate SC the lowest I measured was 9 with the wind chill and on those few nights of bitterly cold air, I broke out the lights, DOUBLE fleece blankets AND a second layer of plastic. The next morning the max/min thermom read 34 !!! Phew. But that was a real pain in the "you know what" each morning and night to work that into my routine. Then sometimes it was too cold to remove the covers before I left for work and had to come home during my lunch hour to remove them before I cooked everything. I spent more money on gas alone during those two weeks to make any savings from the bulbs worthwhile. My life revolved around the hoops..... AAGGHH......However, it worked.

You will find a solution....everyone has unique circumstances. Hang tough and stay with it. Lots of great ideas and support on this topic