If you need to substitute light anyway, why not go for the best insulation factor? It can make a huge difference when it comes to the amount of space or cover between you and the cold outside. I think that even cloudy days are much better with the best insulation. You can always bring in the light, but you will always have the headache of insufficient insulation if you have too little of it.
Doing it now, is better than stuffing plastic all over the greenhouse later. Just my opinion.
PS Will save a huge amount to heat it too.

Our winters are dark-so much that average foot-candle readings with natural light in the greenhouse would be about 400 - which is barely enough for a spider plant!!

If I use 3 1000W HPS lights-it costs me about $75/mo in the dead of winter when it would be needed the most but in summer, I don't think I'd need it at all except maybe on dreary days.

Is there some kind of sensor that can be set to automatically kick on the lights when light levels drop to a certain point??

Sure, there's yard light gizmos that turn on at night in enough styles to suit your wiring expertise. Put it in a shadier area or put a piece of tape over the eye to dilute the strength of the light entering it till you get it to turn on when it's shady enough to need it.

-Ed

I'm just thinking with the 25mm 5-wall stuff I'd possibly even need to supplement light in the summer on cloudy days! Maybe the thinner stuff will be better overall, I dunno.

But - with regards to the "electric eye" type items, I don't want the lights on all night, just during the day as a supplement. Perhaps if I plug the light sensor into a light timer, that would work - to where the light sensor only recieves power between say the hours of 6a to 8p or whatever.

What part of zone six do you live in that you get such little light. Because of heating cost I would go with the thicker polycarb. you might consider putting a lower ceiling in your greenhouse. Take clear poly sheeting and mount it just above your head. This creates a smaller spaces to be heated lowering your heating cost. under the bench heating is better then overhead heating. I have grown with polycarb for about 10 yrs in zone 6 and never had to use additional lighting. good luck

Northeast Ohio. We get a LOT of lake-effect cloudiness in winter. While you and I are both zone 6, our average winter temps are much colder overall than yours-but-our ultimate winter lows are probably similar. IOW we may have a low winter temp of -8 and an average high and low of 32/18 while your AVERAGE might be 45/20 but you still dip to -8 at times. We don't get quite the extremes.

The only reason I'd be concerned about light in summer is because the 5-wall 25mm only transmits 61% of available light.

Today a half hour before sunset it was overcast-my light meter outdoors registered 235 foot-candles. That doesn't sound right to me!

Also, since I want to grow bananas that can top 8 feet-I need the high ceiling.

Hairmetal, I feel your pain in this decision. A guy at a local nursery told me to go with double-wall and rig a method of pulling over a thermal blanket at night just above your highest plants. Then you are only heating that portion of the greenhouse. It would be cool to have all of this automated! I'm sure it's possible for the electrical engineering types out there.

That's my problem. I'm young, not retired, and work 50 hours or more a week. I can't babysit the GH all day!

I'm trying to get a contact with someone from OSU extension offices. No luck yet. I tell you this, there have been some wild-a$$ ideas about heating this structure pitched to me. Solar heating with thermal mass(water or rock as a storage medium) is just one. My head is swimming over all of this and I am one to two years away from building one!! I swear I'm going to put in a big wind turbine and just run the darn thing all electric! Central Ohio has seen more wind in the last couple of years. This system is not cheap either. So what do you do? Big cash outlay up front or be bled month by month? I keep being told to do a "Forida-room" for my plants instead of a greenhouse. This would have to be one big momma of a room stuck onto the back of your home. Besides, they won't be just plants but fruit trees that are going to outgrow a normal sized room. The biggest problem I'm finding is that there is good and bad to every opinion thrown at you. Like you, I have to have as much light coming in as I can get. Do I want to supplement the light? Absolutely not, but I probably will have to because of our crappy, sunless winters. Oh well, c'mon lotto!

personally in zone 6 i think the extra cost and rvalue would be a waste. It is quite dependant although on what temp your goal is and what plants you are trying to grow or just keep alive. A nightime insulation sytem may be your best bet. A lot of research points to plants light requirements being most likely drasticly over done by amatures, and research wiith limiting factors indicates bright sun is probably several times what is needed by most plants. Many plants benefit from 10 TO 60 percent shade during bright summer days. light is probably too expensive to add unless money is no object.Lack of light usually won't kill anything just prevent fruiting and more rapid growth. heat sorces can vary but if you have the time and desire wood is burned off by the ton in most every state just to dispose of it. I heat with wood in my house and it costs just the time to cut and split as well as the fuel to retrive it. coal is the absolute chepeast form of purchased heat. I subscribe to elliot colemans views forget trying to fruit tomatoes all winter and just grow what you can in unheated or marginally heated lowcost structures with minimul inputs. In zone 6 unheated greenhouses should still make cabbage broadbean carrot radish etc etc as well as keep any plant from 2 zones south alive all winter. In my part of zone 6 i saw about 2 weeks with day temps of 20 or less this year. rather than try to remake nature why not just go with a suttle assist shoot for about 2 weeks of heating and keep temps to about minimum 30F-35 depending on what plants you absolutely want to keep alive. My guess is that in Z6 you will end up fighting overheating and condensation more than cold. If you are looking at smaller buildings with more money per spure foot and less ongoing expense look into solar desighn basicly you build an isulated modified Aframe with glazing only at an angle of 40-65 degrees on the south. Another aproach that was pioneered in ontario is a double layer of plastic over a soap bubble water resivore that gets bubbled up when insulation or light difusion is desired and the bubbles allowed to colapse back into the tank when not needed. read a couple of colemans books he market gardens mache salad greens radicio etc in main in unheated and or minimul heat lowcost hoop houses.It is reaaly a waste of resources to attempt to produce tropical or summer fruit in heated lighted houses in winter but it is still quite possible to make zone 6 a yaer round garden with no aditional light and very little if any additional heat.

My MAIN goals are citrus and bananas. That might not work with your method above. If they spend 4 months with inadequate light I may not get blooms that spring and what fruit does set won't be sweet or large. That's what my concern is.

Of course bright sun is more than needed but when you consider that 80% of winter days here don't see a lick of sunshine then you have an issue.

you can fly in a lot of high grade organic banannas and oranges for the cost of a simple hoop house. I did see a website from a guy in nebraska (Z4?5?) that greehouses oranges. some folks in coastal oregon have grown bananna and i don't think the sun ever shines up there 2 days in a row. the french grew oranges under glass first if what i read was right and most of the usa gets more light than they do just cooler temps. It all depends i guess on what you want to do. one theory is if you are gonna have a hobby it may as well be an expensive one. seems like a waste of time effort and money to compete with nature too drasticly. I buy all the banannas i can eat for about a dollar or 2 a week. we have a local grocer who has 18cent bananna day i am sure a GOOD homegrown would be much better. Before all the expenditure can you find anyone else doing it in your area to find out exactly what would be required? oranges i could understand they last on the tree quite a while but what would i do with 75-100 lbs of bananna that will last a week at best? give it to the food bank i guess they make nasty wine. no real way to stagger or preserve the harvest so you are back to buying imported most of the year. feast or famine like so many fruit crops.I know zone 6 is only about 2-3 zones from production of both those items and it gets rainy and overcast in winter in florida and texas as well as up here. I supose people in florida envision refrigerated greenhouses so they can get apple and pear to produce. maybe we could just all pool our resources and barter with those who can easily grow the differant crops. seems like most areas have lots of fruits and berries that are suited or can be produced with low inputs. i would reconsider excessive heating and lights just to produce food. make it safron or vanilla and find a market first if you are gonna spend all that.Z6 is capable of pecan grape hazelnut walnut currant raspberry apple cherry peach nectarine apricot pear pawpaw medler strawberry blackberry plum hickory blueberry all with no climate control fig almond and some citrus should make with very little climate control. we do have bananna in our local zoo that makes on occasion and the lighting is much more limited than in standard greenhouses.Only the roof is translucent and it is very clouded material.

Growing it myself is the fun part.

Hairmetal...I guess he just doesn't see the point. If I wanted store-bought fruit, I wouldn't be on this website looking for info on greenhouses! We love the challenge of growing things NOT grown in our regions and most of all, we love the challenge of growing things people tell us that we CANNOT grow in our region. What hobby is not usually a waste of time, effort, & money? Hell, if it wasn't, I don't think it could be legally classified as a hobby!! If I can get my stuff to bloom and fruit during the winter in a spare bedroom with a metal halide grow light, I darn sure ought to be able to do the same and more in a greenhouse. Is it going to cost me? Oh yeah. I'm here to find the best methods of keeping those costs down. If the plants I wanted to grow only required minimum light and could survive and thrive at cool to nearly cold temps in the greenhouse, that would be great. However, what I am interested in requires much higher lighting and much warmer temps. Also, can I purchase any of the fruit I'm wanting to grow in the local grocers? Absolutely not. A few of them cannot even be obtained in this country...except Hawaii and they cannot ship. Hopefully those that don't understand our passion can now get a small peek at what drives us. J

I already told you how to keep your costs down forget about lights you don't need them for most fruits to make.

There's no point putting citrus in my GH if the light levels from Nov. thru March (RIGHT when they are ripening fruit) are too low-my problem (which you have NOT addressed) is that this time of year is when citrus fruits ripen and bloom and if light levels are the average of deep forest shade in summer (or worse) I just don't see how well they will do. What I DON'T want to do is spend thousands on a greenhouse and find out I was better off inside the house. Sure, I could then retrofit some HID lights but I'd lose a season or two of fruiting potentially. Bananas would probably do OK since they bloom after reaching a certain number of leaves regardless-as long as they survive and don't die to the ground, they'll eventually bloom-citrus is much different.

Mark-have you grown citrus??? Maybe I'm wrong-but-I have only fruited them indoors with a strong (1000W) HID light-with even a south-facing bay window and natural light indoors they barely survived, dropped their fruits, and lost a lot of leaves (last winter). This year, I have several fruits ripening and blooms setting new fruit. The light had to make the difference.

BTW-does this guy in Nebraska use any supplemental light??? I don't know what city he's in but I went to this site below using Lincoln, Nebraska as an example (doubt the rest of the state is much different) and they get TWICE the winter sunshine that we do!! We get 26% of possible sun in January and they get 55%. I'm sure that makes a huge difference. I'm telling ya-while our winters aren't brutally cold, they are dark. Several days go by in a row on many occasions where drivers leave their headlights on all day during the dead of winter here.

Here is a link that might be useful: Lincoln, Nebraska sunshine

nope the guy in nebraska does not use lights. It sounds more like you are trying to figure out how to manufacture drugs and i don't think anyone here will be able to help you with that.

I am in no way trying to grow pot. Don't be a jerk. I just don't think you have any concept how little sunshine we get in winter. Check this out:

Here is a link that might be useful: Akron, OH sunshine stats

Whoops-wrong link, try again:

OK, so we get 30% of January sunshine. That's still barely half what Lincoln, Nebraska gets. In fact, almost every other place you can think of gets more.

Here is a link that might be useful: Akron, OH

ok so i just compared akron ohio and brownsville texas a citrus producing area and guess what only about a 25% differance in winter. do you really think that is going to be critical i do not. as i said most people oversetimate the need for light and most plants get more than they really need even citrus i have seen recomendation for shading from mid day sun. Untill you try or find a university that has how will you know? Once again you don't need no stinkin lite. Most plants store energy when the sun shines and want to live and fruit so adapt to adverse conditions reasonably well. Some of the best fruits are produced during some stress such as drought temps lite levels etc. why not just move to brownsville or miami and just grow em in the yard? citrus also ships quite well and you can find mail order supplies of very high quality produce most likely much better than you will ever produce even if you spend 20x as much. I still say if england and france can grow oranges under glass with no light ohio should be even easier.

Well, maybe you are right Mark. Keep in mind in Brownsville being at a much more southern latitude would have more intense light even on a cloudy day than we do, so the amount of light reaching the plants will be a good bit more than 25% more than here, plus the days are longer. Here, in June, if the day is cloudy, not dreary, just a typical dry but cloudy day, midday light intensity is 1500 foot-candles. In December, same weather conditions, would be barely 500, which is pretty low. Inside a GH is 50% - 80% that when you figure in glazing and shading from framing. In Brownsville the December sun is as intense as our sunshine in May-so it would be much more than 500 foot-candles under a cloudy sky.

I don't want to move to Brownsville-that isn't the point. My family, job, and friends are here.

Again, the point is to grow it myself. Sure I could buy them, that's not the point.

Hairmetal, it all comes down to logistics. Do you have room to continue growing what you have and want in the future in your current settings? If not, then you are like most of us and want/need a greenhouse. I have my stuff in a spare room and can't stand it. Too small and the light causes the upstairs to be about 15 degrees hotter than the rest of the house. Disease and pests are also a pain and spread too quickly and harder to control. How many times have we spilled something all over the carpet or worried about spraying something in the house? My spare room cannot remain my greenhouse much longer. I agree with you that we will need some light supplementation. I know I will for my plants. Not just for fruit but for rigorous growth. You sound as if you know what you need. A lot of citrus need sun/light to sweeten up. I don't think I would go so drastic as the 5 wall polycarb. It will cut down too much light year round and there's other things you can do inside the greenhouse to help maintain the heat. Another thought on citrus is that they can tolerate the cold much better than a lot of other tropical fruits. A guy in Michigan has a double-wall poly carb greenhouse. He used hot water pipes in the ground to heat up the soil for all his potted plants. He has citrus and bananas and he told me they do fine as long are their roots are warm. He does no other heating besides that. Inside temps are high 30's during cold snaps and no problems with his plants. I don't believe he supplements any light but I have to say it would benefit them. Here is the link to his site.
http://mysite.verizon.net/grabshot/

All this ink wasted about heat and light. I am in zone 6. Dec, Jan and Feb are 3 months where we have more than 50% of the days with no sunshine at all. The stats for last year indicate that we had just 63 sunny days all year, and more than 110 days of measurable precip.

My citrus does fine. We have 2 kinds of lemons, a non-bearing orange that is blooming as I write this, and a grapefruit tree that I wish would die so that I could compost it. (DW's tree, has immunity from trash.) The temps in the greenhouse range from about 75F/24C to 25F/-4C when the heater malfunctionned. More typical are the nights when the thermo. is set at 45F/7C. Lemons are supposed to need more heat than oranges. Limes need more yet. Oranges are not a 'true tropical', so low night temps are not only tolerated, but the tree will like them. The fruit will color better and quicker, and the number of blooms will be increased.

So far as bananas, the only one I have in there at the present is M. basjoo, a plant that is marginally hardy here in Zone 6. Bananas are true tropicals for the most part, and I don't think mid-40's F will do them any good. When I grew them outside in FL, the cool nights in the winter (low 40's usually) didn't hurt them, but they came to a standstill so far as leaf production, etc.

I have a question. How did you figure that it would only cost 1/3 the energy with the thicker stuff? 3X the R value does not translate into 1/3 the fuel, but maybe I am reading your post incorrectly.

Using a BTU calculator I figured that out.

Where in PA are you, Pete?? What kind of glazing do you have on your GH? How big is it? What are your heating costs? Your min temp of 45 is about what I'd want (maybe a tad warmer w/bananas...low 50s).

You made it work with no additional light, maybe I can as well. I guess I just feel better having that available, considering the only way I get citrus to fruit inside is to put them under 3000 foot-candles of HID light and let them summer outdoors.

I am in the south central region of PA, SW of York, PA. The glazing is glass, and I don't use any lights for growing. Size, 12'6" X 26'6" (3.8m X 8.1m). Heat, about 300 gallons of propane/yr. I have a fan that runs 20hrs/day. Most of the plants in there are cactus/succulent. Cool nights preclude many Arums, but the high humidity favors some rainforest cacti, strangely enough.

Whatever you choose, build it as large as you can afford. Mine was a rare find for 500 bucks, and that included most of the glass, all the frame and the aluminum bolts to put it back up. I have friends with double walled jobbers, and they are cheaper to heat, but the esthetics are different. Theirs also produce thousands of dollars of food, mine gives me occasional cactus fruits and lemons for a couple of months.

Each greenhouse also has its own little climate. The materials used, the orientation and the outside climate all combine to make individual little biomes. A for instance: most folks would think that a carpet of moss in the pot of a cactus would mean the cactus would rot. Not so, and I can send you pics of many species of succulents with a solid moss covering on the soil. The air is humid, but the soils are dry, and the moss thrive in the cool damp air. It looks really good too. So the climate in mine favors moss, succulents, tropical epiphytes (jungle cactus, bromeliads)and cool climate citrus, and kills Aglaonemas (leafy Arums in general), Polypodiums and Sansevierias. The point is, while you can get much encouragement, ideas and information from a bulletin board like this, after you set up your greenhouse, it will show you what you can grow. Change the conditions, change the plants. Lots of bucks and cheap fuel? Growing orchids is possible. Shallower wallet and heat costs a consideration? Cacti make good pets despite their prickly reputation.

Nice thing about a light - you can add one anytime you like.

Multi-layed sheets, or add another layer later.

As Pete put it so well, everybody's setup will be different, too many variables to predict what will be needed without doing a trial in your own yard.

I've radically altered mine every year. Started cheap and built it up as I went.

I bought a ph/light/moisture meter for $7.50 a couple days ago. 2000+ outdoors, 1000-1500 in the "translucent" twin-wall poly-paneled gh. I'm happy so far, we'll see if the plants agree!

-Ed

Ooh...well that's disturbing. So my winter OUTDOOR readings of 450 would translate to maybe 250...looks like without lights I'll be growing Pothos and Philos!

There's a local greenhouse here with a citrus area and they told me that their oranges are bitter but they grow lemons OK.

Which means several things but too little light can cause the fruit to not sweeten properly!