I set up a spreadsheet much like the sunnyjohn calculator, and ran some numbers for my climate, Edmonton, Alberta. I came to the conclusion that in this climate I needed to double the depth of the layers. E.g. 6-8 foot deep. This starts getting awkward, as they don't rent ditchwitches that do a narrow trench that deep. Ballpark calcs: The worst case is a 'frozen fog' weather cycle. Cloudy days, so minimum heating, coupled with temps of -20C (-30F). Given an R2 greenhouse (typical for 2 layers of poly with an inflation fan, then every square foot of surface has a 90 degree temperature differential across it. Because of the sides of a hoop house, I am going to make the approximation that there are 2 square feet of outer envelope for each square foot of ground. This is pessimistic. It's somewhere between 1.57 (pi/2) for a very long green house and 2. So each square foot of greenhouse floor has to store heat for 2 square feet of R2. With a 90 degree F temperature differential, it takes 45 BTU/hr x 2 square feet = 90 BTU per hour. Again, being pessimistic 5 day operation = 120 hours. So 90* 120 = 10,800 BTU The heat capacity of dirt is about 1/3 that of water on a volume basis. Call it 20 BTU/cuft/F If we are willing to let the greenhouse temp drop 20 degrees, then each cubic foot can store 400 BTU. That would mean 25 cubic feet of dirt per square feet of floor. Ouch! If we are willing to go 2 days, it's easier. 2/5 as much heat = 10 feet. Saving grace: If we are are going for long term heat storage, the tubes can be further apart. Sunny John estimated on the basis of storing 1 days heat, so his pipes were a foot apart. If you want 5 days heat, you can put them further apart. It starts to make sense to drill vertical holes instead. E.g. Drill a 1 foot diameter hole 20 feet deep every 5 feet. Each one gets a loop of pipe going down and up. This does make for a less efficient heat exchanger, as the air going down will transfer some heat to the air coming. Worst case, the air out will be the average of the ground temperature and the air going in. E.g. With 50 degree ground, and 80 degree air, you will get 65 degree air coming out of the ground. This ignores the latent heat factor. You might be able to get better efficiency with concentric pipes, but this makes the plumbing complicated. A cheaper way to do this may be to dig a pit 3 feet deep over the entire interior space. Put barrels in the space, filled with water, with a bit of space between them. Put in a lightly insulated floor. (R4 should do.) Barrels are about 22 inches. Put in a 2 inch space, and you have 1 barrel for 4 square feet. A barrel has 480 lbs of water. A 20 degree temperature variation is 10,000 BTU, plus whatever heat goes into the ground below the barrels. But that's for 4 square feet, so it's 2500 BTU/sqft Would do for a day and a bit of our worst case. Lets look at a different solution: Natural gas. Winter gas prices are about $6/GJ and a GJ is about a million BTU. So our one day worst case is 2000 BTU/sqft. That .002 GJ will cost us about a cent a day. How much digging are you prepared to do to save 3 bucks a year? That's worst case too. It's not always that cold. Actual greenhouse operations are worse than this. When plants are actively doing their photosynthesis thing, they will use up the CO2 in a greenhouse in about 10 minutes. So you need an air change, or another source of CO2 every 10 minutes. Air has about the same specific heat as water on a weight basis. A cubic yard of air is about 2 lbs. Your square foot of ground with a 15 foot ceiling has about a pound of air to heat. Heating from -30 to +60 takes another 90 BTU. Every 10 minutes. So the air heating load is 6 times the building heating load. However, no sunlight, no photosynthesis. And when there is sun, it's providing even in winter about 600 W/m2 which is 200 BTU/sqft/hr One greenhouse operator near here heats water in the day, pipes the CO2 into the green house to help the plants, does an air exchange every few minutes on top of that, and uses the stored hot water at night. They claim energy costs of $3.50/square foot. Conclusion: It's a cool idea. If you are off grid, it's a great idea, especially if you have sunny winters. Is it practical as a 'best solution' at current energy prices for a cold climate? I don't think so.

Jim Kohut describes Morden 9703 (S16) - A recently introduced (and as of yet unnamed) hybrid from Eastern Europe, this is undoubtedly the hardiest green table grape you'll find. Produces absolutely enormous clusters of large green grapes that are incredible for fresh eating, especially if left to ripen on the vine into fall - these will rival any table grapes you'll find in the store! Hard to find in the trade. Marginally hardy in zone 3 - may need some winter protection." Make it Green garden center lists it, whether it is what they say it is is another matter. The front here would be Prairie Star but I was busy and the vines co mingled together...I did trim a few times but the wet summer created a lot of vigor. The clusters look good but I will have to follow the cordons back as they should not be colouring. If they are they would most likely would be the Frontenac if the clusters continue to change colour. There was no die back anywhere but this was an unusually mild winter. Probably could be described as a zone 4 rating. Frontenac on the left.

Hi M I, Ouch! You dont just live in the middle of Coloradobut in the middle of the mountains! Its definitely cold, but it sure is beautiful out there! I love the overlook just east of Buena Vista that faces the entire Collegiate Range, and I stop for the view whenever Im going by that way. The planter boxes youre talking about would probably be big enough to plant vines in, but doing so would be pretty iffy, and I dont recommend it. The thing that kills plants over winter isnt the cold, its when they freeze and thaw and freeze and thaw over and over. And with ouror yourcold nights and then very warm, sunny days, the planter youre describing would probably be freezing and thawing repeatedly in winter, so you could never be sure they were going to come back the next spring. Watering in an above ground planter over winter would also be harder since it would dry out fairly quickly, but youd need to be sure you werent keeping it too wet either. Things planted in the ground have much more stable moisture conditions. Vines planted in the ground wont take up very much roomthe worst problem would probably be cutting through the existing roots to get them planted in the first place, but after that theyll just grow in around the roots of the other plants, and most of the foliage would be directed up onto the pergola. And I seriously dont recommend planting any of the invasive ones. I think youll regret it later if you do, and if theyre planted in among the lilacs and roses, it would be even harder to try to kill them off without damaging the "good" plants later. I would definitely recommend staying away from the first 4 I mentioned! I didnt think there were any table grapes that were hardy to z4, but if Davids right, I think that would be a wonderfuland deliciousidea! And I completely agree about the "Welchs grapes!" Concord arent especially good for just eatingeven the seedless onesbut they used to be considered the hardiest ones, so I kind of assumed that would be your only choice if you went with grapes. Ill be anxious to hear what varieties you have, David. And I didnt even know you could get shade cloth in pre-cut pieces, but I completely agree with David on using the shade cloth until your vines provide enough cover for you. Thats a much better idea than planting one of the "thugs" just to get fast cover. I can just about guarantee youll be MUCH happier down the road a few years if you do it that way. Regarding the Wisteria, Id be a little bit leery of that one, because back when I was in the green industry we sold quite a few of them, and every single year wed have a bunch of people coming in and asking why their wisterias never bloomed. We never came up with a definite answer, but as near as we could figure out, almost every year we were getting a freeze just as the buds were beginning to formbefore you could even see themand that killed the buds. I dont remember anyone ever coming in during those years telling us about how nicely theirs had bloomed. One thing I do agree with Steve on is that when they do bloom, theyre absolutely amazing! Among the most beautiful vines Ive ever seen! I used to commute to San Francisco, and the girl I stayed with when I was there had one growing over a LARGE arbor type thing leading up to her front door, and every spring it was really indescribably beautiful, but I think youre in the wrong climate here. But, hey, weve got lots of beautiful things here toosome of them are called mountains! LOL And if the flatlanders down here in Denver cant get them to bloom, Id say its even less likely that youd be successful out there in the hills. If anyone knows of a wisteria that does bloom here in the Denver area, I sure would like to hear about it, because ever since I saw a picture of one as a little kid Ive wanted to have oneand then decided to not waste the time after hearing from so many customers about them. At least I got to "experience" one for a couple years out in San Fran. Do let us know what you decide to plant when you finally make your decision, Skybird

Thank you all for your input. I narrowed it down to: Madame Alfred Carriere (Positive: can get large, beautiful flowers, thornless, I consider it one of the best fragrances in the local rose garden, one review on HMF says does well for them in this climate. Negative: does not seem to be a monster in this climate and not much bigger than 8 feet in the local rose garden; tried it once and it died despite coddling, said to be very susceptible to thrips and the thrips are horrible here). Barfield White (Positive: can get big, lovely flowers, thornless. Negative: upon research it was trialed here in Albuquerque and the report was that it did not want to grow in this climate). Paul's Himalayan Musk (Positive: Can get big, said to smell great, beautiful flowers, sold by High Country Roses so might well in this climate. Negative: reports of very short bloom season as short as one week according to one report, and said to be not fragrant in dry climates, no examples locally). Mel's Heritage (Positive: can get big, blooms a lot, good fragrance reported. Negative: I don't really like the flower form - I don't like the quilling, thorns). Cécile Brunner (Positive: the ones down the street appear to be happy to grow, gets big enough, nice flower form, longer bloom season with possibility of reblooming form; Negative: fragrance varies, small flowers, not sure about the color. Also, SO common, which is both good - should be easy, and bad - boring?). Rambling Rector (Positive: big, fragrant, impressive, nice hips for fall/winter color. Negative: thorny, brief bloom season). New Dawn (Positive: gets big, reblooms, some fragrance, nice flower size. Negative: very thorny, I'm not that fond of the flower form or color, not sure if the size and plant shape will work well with the pergola). Other options: Wisteria (Positive: gets big, beautiful flowers that fit my color scheme, fragrance; Negative: gets BIG, brief bloom season, messy with leaves and seed pods, requires a lot of maintenance and I'm not sure I want to be balancing on top of a 10 foot pergola multiple times a year). So in the end I settled for Cécile Brunner, since it would be much more likely to be successful in this iffy climate. I still wonder if I should have tried Madame Alfred Carriere (since I do love that fragrance!) but I think that would have been a much more risky choice.