These look really good Tony!
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…but if someone was planning multiple trees (like varieties of bananas and mangos) in-ground in a greenhouse long-term it’s totally feasible… yeah?
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Yes, just as long as it’s the right kind of greenhouse. Big enough, can cool down in the hot weather ‘like opening up or air conditioning’, has a decent reliable heater for the coldest part of the winter.
What about heating by building (winter only) large compost piles along the walls on the outside for Z7B?…
One of the more popular methods for ‘less energy intensive’ heating is in-ground pipes to draw heat from the ground. Search “citrus in the snow” on YouTube for a popular example. After that there’s a huge rabbit hole of more refined examples.
Insulating the north wall will help a lot. And even recessing it into the ground (especially feasible for ‘tall crops’ like fruit trees).
There’s also YouTube videos about heating with compost, and also historical accounts from hundreds of years ago. But it seems to not be an overly popular method these days. I’d think you could get much better results by running a tube through the compost pile to better siphon off the heat?
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This is a very interesting idea! A heat pump powered by microbes…
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One thing that is done to heat greenhouses in the winter, is freshly made compost spread inside the greenhouse, when it’s freshly made there is a lot of natural gas releasing from the compost that warms up the greenhouse. The thicker the layer of the compost the warmer it is, I have never tried it because we don’t have enough compost to do that, and we never will. We don’t even have enough for our regular gardening.
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Totally trying the compost heat pump on my new SC property, thank you so much for the awesome idea!
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Unless your compost heat pump can produce a few thousand watts worth of heat for several consecutive months it’s not going to be enough in Z7. Winter nights are cold and long.
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Actually Zone 7b varies a lot from one location to another. Also the bigger the greenhouse the more heat needed. Like zone 7b South Carolina is very different than zone 7b NYC, and than zone 7b Washington.
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For banana and mango in Z7 you need a heater. Even one night below freezing can set you back by years.
I’ve tried the compost pile in winter in my greenhouse to increase CO2. It works great for that. I’d be concerned that if the pile was big enough to produce anywhere near as much heat as needed that CO2 would build to dangerous or at least unhealthy levels. I also had a huge fungus gnat issue with the compost.
Also think what tons of compost in a greenhouse would do to soil nutrient levels. They’d be thru the roof. There’s a reason, and likely many reasons, that you’ve never really heard of this being done.
The geothermal soil heat battery is a good idea but expensive to install and still not adequate for things that can’t tolerate any freezing. I’d want a backup heater.
With any greenhouse summer cooling is just as important. Most people build a greenhouse with inadequate cooling and end up relying on heavy shade cloth that reduces light levels a lot.
In a dry climate a wet wall opposite large exhaust fans is the best cooling option. My greenhouse seldom gets above low 90s.
The other thing about passive methods of heating and cooling, ground battery heating and natural venting of heat, is that to some degree you lose control of temperature. You get what you get. Think about whether that’s good enough.
With a heater and wet wall in my zone 7-8 greenhouse I’ve had winters with 1600 chill hours and winters with zero chill hours. I control what I want and how I want it depending on the crops I have growing.
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The 36 x 96 house sat on a pad of washed stone, single layer greenhouse clear 8 mill cover. No heat, double fans/vents thermostat controlled. We are right up against a lower zone change, so we can get get some winter weather that slides down the scale for a few days/weeks, the map shows #7. Grew large specimen tender+/- herbs and they wintered well. Lavenders, rosemary in 3-5 gallon squat containers made it through, never tried any trees however.
Haven’t been able to keep fig trees living here outside even against a south facing wall. Imagine they would have been ok under the cover.
Winter greens will be no problem, maybe control the soil better in large pots or beds, put down landscape cloth on washed stone before erecting structure. Used the black lined cloth under the stone as well.
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I agree with @fruitnut heating is actually pretty easy, but expensive. Buy a couple heaters with temperature sensors and you are good. Cooling is more challenging. When it gets to 100 degrees your greenhouse will be cooking without a good evaporative cooling system. I use shade cloth, but it is not ideal. My greenhouse got up to 120 degrees last summer and my mango didn’t seem to mind. The hard part about Mangos is that you have to use rain water. They hate my city water. They are also very sensitive to fertilizer with a lot of micronutrients. I am still trying to figure out the right amount for them. If possible I think geothermal would be a great option, but prepare to pay quite a bit for installation. You could also look into a heat pump if you are putting underground piping in and geothermal is not accessible at your site.
My theory: if the pile were so large— it would only take a little air vent at ground level with maybe a 6 volt fan blowing at it. Heat rises, CO2 drops— sound kosher?
A small exhaust fan at ground level should help a lot to lower CO2. A fan blowing at a vent, no. If you want to vent heat, CO2, or anything else an exhaust fan is best. To vent heat have the exhaust fan up high. To vent CO2 down low.
It’s like comparing a wet wall and exhaust fans to a swamp cooler blowing cool air in or worse yet a swamp cooler just inside with no outside air exchange. Exhaust fans remove the hottest air and replace it with the coolest air, that coming through the wet wall. A swamp cooler blowing in mixes the cool and hot air and blows a mix of those out the vents. The latter is less efficient.
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At what avg humidity level would you say it’s no longer worth using a swamp-cooler? I’ve only used them in high-desert areas (where they work magic of sometimes dropping temps nearly 26 deg fahrenheit)
I’d still do a wet wall and exhaust fans in SC. But the results will be less than in west Texas. Our summer dew points are 55-65. In that range it is a very effective cooling method. Above 75 dew point it’s really tough cooling a greenhouse by any method. You’ll probably need some shade cloth in that area.
The roof on my greenhouse is covered in an inflated, double layer of Solarig. The Solarig and newer Palring are highly effective and long lasting greenhouse coverings that reduce heat loss at night in winter and heat gain during the day in summer. That plus a wet wall/strong exhaust fans and about 30% shade cloth on top should be about the best you could do in the humid southeast.
Solarig and Palring: Greenhouse covers and ground covers (robertmarvel.com)
My Solaring was guaranteed for 6 years and has lasted 10 so far. It’s far superior to normal 6 mil greenhouse poly.
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