Mike's passive solar greenhouse design/build

Wow, two months without an update?!?!?!  I guess the spring and summer homestead projects are getting in the way.

Since the last photos, I've done very little construction.  I added a handrail to the platform above the compost bin.  It's turning out to be a nice place to lay and soak up the rays.  Can't wait to do that in the winter when I'm looking to get warmed up.  Still need to do the handrail along the catwalk...

I purchased some vent openers called Vent-L from Russia.  They supposedly were the strongest vent openers on the market, capable of raising a 220 lb vent.  They didn't work.  So I got two Gigavents instead.  They have three pivot attachment points so you can set them to be stronger with a shorter opening distance or weaker with a longer throw (or in the middle).  I put the first one in the middle position and it worked!  I put the second one in the weakest spot and it still operated and opened the vent further.  Yay!  That's pretty cool because the vents are 4' by 8' with a 2x4 pine frame, 4" of polyiso insulation and steel roofing on the outside.  So they probably weigh 60-80 lbs each.

So far I've found that they both start to open when it gets up to 80F in the greenhouse at ground level.  Perfect for my needs (I think).

I have two of the lower vents open all the time, as well as one person door.  Then as it heats up, the upper vents will open and let the excessive heat out.  I'm still waiting for a hot sunny day (90F) to see how hot it gets in there.  On an 80F sunny day it stayed a bit under 100F inside.  If I can ventilate this huge sun trap of a greenhouse with just two upper vents, I'll be ecstatic

In the plant department, the seedlings all grew up and got planted outside.  Some are in the front planting bed (peppers, tomatoes, cucumbers, holy basil).  A patch of peas is in full production and we ate peas on June 1st.  I potted up the citrus trees to a larger set of pots a few days ago.  Yesterday my papaya, coffee and pepper (piper nigrum) seeds arrived so I got them planted.  Bananas, dragonfruit, mango, avocados, miracle berry and finger lime trees are on order and should arrive any day now.

I'll put most of those in pots and probably start some more ground cover plants and other legumes growing in the ground in the mean time.  Nothing too valuable in case I have to dig it up to run waterlines or something.

Last night we sat out there at dusk plotting where the big trees will go (so we could plant papaya seeds in the right spots).  A few frogs have found their way into the greenhouse and they started singing and it was deafening.  It will be neat to see if our local frogs will stay active and overwinter inside the greenhouse.  Otherwise I may look into some tropical frogs and snakes to add some life to the place year round.

Looking good! The height on the greenhouse makes for an amazing building (2.5m height restriction on garden buildings where I am!).

I wish you well with the tropicals. I failed with papaya this year (nothing germinated), but my coffee plant has ripening beans on it! It is exciting growing stuff you 'can't' grow in your climate.

Thanks Charli!  Yes I love the height.  It's about 17' high to the bottom of the ridge beam.  Should be plenty of room for the taller trees.  Or a ton of potted plants along the catwalk.

Just got the new property tax assessment.  Apparently the tax man thinks it's worth $16,300.  I'll probably go along with that

I don't even really like papayas but they're supposed to be a fast crop, they don't take up much room and they look really tropical.  We'll see...

Hey there. I am working a greenhouse design in Maine and was wondering if I understand correctly that your foundation was only 7 inches deep? No trouble with heave so far above the frostline? i am looking for a design that uses minimal amount of concrete. I have been thinking of just some beams at grade on bigfoot/sauna tube piers but found your design interesting.

Hi Peleg, yes the footing is shallow.  Anywhere from 7" to 20" deep due to the contour of the land.  I think it's called a Frost Protected Shallow Foundation.  It would heave if it wasn't for the styrofoam that I installed down a foot along the outside of the footing and then out 3'.  My frost depth here is 4' and that doesn't have to be in a straight line.  So the frost has to go down a foot to get under the skirt of styrofoam and then travel 3' under it before it can get to the foundation.

No problems yet.

I've been working on other homestead stuff this summer but I'm due to take some photos and get an update on here.  As a teaser, I have bananas in the ground

Mike, I don't know what's taken me so long, to find this! I LOVE your greenhouse - It sounds like it might be the answer to some of our concerns and needs, here, because we want to do some tropicals. So, how is the heat, this summer, in there? Not building too much, I hope?

Hi Carla, I'm glad you found the thread!  I'm really delinquent about posting updates.  I'll do that today (by golly).  The vents are working great!  I have 6 patio doors at the bottom of the south wall mounted on their side as vents that can swing up.  I have two permanently propped up for the summer.  That lets cooler air in any time it's needed.  At the top (17' up) I have 5 big 4x8' vents.  Two are on automatic vent openers which open and close as needed.  In the heat of the summer I have a third vent propped open up there as well.  I also leave the person door open at one end of the greenhouse.  Between all that, on a 90 degree sunny day, the warmest I've recorded is 105 inside.  So I'm loving it so far.  I think I'll need to add a vent opener to one of the lower vents for the spring and fall.  I don't want to leave those propped open when it could get down to 35 at night but they need to be open when the sun comes out and it's 60 during the day.  And I'm too unreliable to open and close it daily

Ok, here's what's going on in the greenhouse.  On the structure of the building, I've installed the ground rods and connected up the electricity.  Yay!  No more 100' extension cord from the barn.  I just ran one outlet so that I could have an extension cord inside the greenhouse.  Wiring the rest of the boxes will probably wait till fall/winter.

I also got the East door threshold and weatherstripping and door knob installed.  Previously the door was just wired shut but I finally got that part put together.

We also trenched rainwater over from a series of 6 IBC totes and we have low pressure water in the greenhouse.  I will be getting a pump and pressure tank so that I can pump that water as needed.  That same pump will draw water from the sand point well that I still need to drive a bit deeper.  Rainwater in summer, well in winter.

And I caulked the exterior (got the siding up way too late last year) in preparation for paint.

On the growie front, things are coming along.  A real gardener would have more stuff in there for sure.  But I ordered the tropical plants once the shipping would be safe from cold temps.  I bought:

Coffee seeds

Papaya seeds

Piper Nigrum (peppercorn) seeds

Nam Doc Mai mango

Australian finger lime

Shasta Gold mandarin

Miracle berry

Two avocado cultivars that haven't arrived yet

Two dragonfruit cultivars

Gran Nain and Double Mahoi bananas

We planted most of those things in pots so that I can move them as needed.  The bananas and papaya seeds went in the ground since they grow fast and were cheap.  For the bananas, I dug out a bunch of dirt (probably 10 gallons) and amended it 50/50 with leaves/poop from the chicken run.  They LOVE IT.  I can't believe how fast those bananas grow.  They went into the ground on July 10th with 3 and 2 leaves respectively.  Now they have about 8 leaves each.

I also got some fig cuttings from the wonderful and awesome Greg Martin.  Most didn't make it, probably due to bad parenting on my part.  But two survived and are doing well.

I also picked up ginger and turmeric from our organic food store and have them tucked around in the beds.  We've saved all our pineapple tops and have many of them started as well.  I also realized that the piper nigrum seeds look remarkably like peppercorns.  Since none of the purchased ones came up, I planted about 50 peppercorns in the beds.  Hopefully at least one will grow.  Lastly, I found a vanilla orchid at the local greenhouse/florist and brought that home.

In the south planting bed the peas have run their course and have been removed.  The cherry tomatoes are about 10' tall and trellised up strings that I keep moving down the line.  Cucumbers are doing very well and we've eaten a half a dozen so far.  Peppers aren't doing great.  They're ok but despite planting them inside a month earlier, the outside peppers are now ahead of the inside ones.  But they are great at attracting aphids so hopefully they'll help the predatory bug population grow.

My main concerns along the growie front are:

Is my mango flowering?

Most of the citrus doesn't look like it's growing.  I'd've expected them to push new growth this summer.  I've had most of the citrus for a year (lemons, calamodin, key lime).  I fertilized a bit this year and gave them an iron supplement (per this thread) and added some coffee ground to help lower the pH.

I have the plants in clay pots and have been watering them well once a week.  Bananas twice a week.  I think for the rest of the summer I'm going to bump that up to twice a week for everything except the dragon fruit and pineapples

Oh, one more activity has been happening.  I opened up the compost bin to remove the failed wood chip compost material and use it in the food forest.  The pile had settled 10% and the surface was fully damp.  As I dug in, the top foot was damp.  Under that it was bone dry (drier than it was when it went in).  In the wet parts it was 110-120 degrees and in the dry it was probably 100.  When I got to the dry bits that were in the center of the pile they were warmer, probably closer to 120.  So it's been gently composting all this time but nowhere near fast enough for my needs.

Due to the poly plastic that forms the lid of the chamber, condensation forms there and drips back onto the pile.  That's why the top layer is damp and the center gets more water than the rest.  

So I think what I learned is that I need to get the pile wetter when I build it.  I may need to add water during the composting season.  I think I need more N to get the pile hotter and to complete its composting by spring.  The wood chips seem to be small enough so I don't think I need to run them through my chipper.

I think I'll divide the chamber in half (E/W) and try a different recipe on each side.  One or both sides will get shredded hay mixed in to increase the Nitrogen ratio.  One or both sides may get a bunch of coffee grounds (20 to 50 gallons) to also bump the N.  One side may get run through my chipper to test smaller wood pieces.

I just picked up this thread. Great work with the greenhouse. I'm taking it all in for planning when we put in our greenhouse.

Greg Martin wrote:That is a great question.  My speculation is that it has to do with being a granular sponge.  I don't crush mine, I leave it at the full size it's made at....something like 1/2 - 1", but lots of other sizes too.  Then I lay 2" on the ground to sop up any compost drippings while creating an air permeable base.  The rest of the pile has it throughout and it may help open up air channels there too, albeit not as much as the base.  Since the biochar can fill up with water, but also space things open a bit for air and drainage I figure it does that in the pile like it does it in the soil.  Also, all the wet surface area in the biochar is a home for soil microbes, so that likely helps in the pile as well.  I should really try and examine my biochar more throughout this process.  Would be fascinating to see exactly what's happening in that microcosm.  I wonder if I can get a university soil scientist interested in my compost piles :)  Hmmm, any of you guys a university soil scientist?

Greg, I saw your post on the issue of heating of the biochar compost pile and I'm not a soil scientist but I might be able to add to the discussion. I've spent most of my career developing and testing sorbents for cleaning up gas and water streams from coal fired power plants. One of the unfortunate incidents we had when we were testing our mercury capture technology full-scale (injecting fine activated carbon dust into the ductwork and collecting it in the particulate collectors) was that it ignited in the collection hoppers. I can hear it now...what the heck does that have to do with my compost? After six intensive months of investigation, I proved that the activated carbon was heating up in the pile of collected ash/carbon due to the build up of heat of sorption of oxygen, moisture, and other chemicals in the gas. Greg, I know you know this but for others not in the business, biochar is essentially non-activated carbon. It doesn't have the high surface area, pore structure, and surface chemistry as AC but it still a good insulator and really good sorbent.

One quick way to check if the sorption of water and oxygen are responsible would be to wet the biochar and leave it for several days/weeks moist to come to equilibrium with the surrounding conditions, then add it to the compost. Any additional heating should then be from other sources, such as microbial activity.

Right off hand I think the compost pile with biochar would heat up due to:
1. Heat of adsorption of water (heat of hydration)
2. Heat of sorption of oxygen (heat of oxidation)
3. Heat of sorption (both adsorption and chemisorption) of other chemical constituents such as ammonia in the compost
4. Microbial activity, especially once colonies are established in the biochar.

A really cool test would be to have several compost piles with varying amounts of biochar in them. Measure the temperature in the dead center of the pile.

Adding biochar could be a great way to heat up compost for those of us too lazy to make our compost piles the right way all the time.

Thanks Robin for reminding me about the biochar!  I need to read through my own thread once in a while  I don't have much char stockpiled but I probably have a couple chicken feed sacks full.  I'll throw them in for sure.  I have perforated drain tile at the bottom to blow air in through.  So I probably don't need a layer at the bottom for aeration.  So I'll probably just mix these sacks in as I build the pile.

I also realized I could use the garden clean up debris as a feed stock.  Tomato vines, squash vines, bean vines, etc.  It may not be super scientific since the amount and type of material may vary year to year.  But it's a good use of on site resources.  I'd still compost them if I didn't use them in the greenhouse...

Most of the citrus is pushing new growth (phew).  I was worried since they have just been sitting there for the past two to three months and looking more and more tired.  The lemons are flowering.  The miracle berry is not pushing growth and just looks tired and a bit yellow.  The Australian finger lime doesn't appear to be growing but it looks happy.  The bananas are exploding.  I can't believe how fast they grow.  I'm peeing on them daily and putting all our oversized green beans on them as mulch.

Greg's figs are growing well and my coffee plants (from seed) are doing well.  The turmeric and ginger tubers haven't sprouted yet, nor has the piper nigrum (peppercorn).

Peppercorns from the store are usually boiled as part of the process, so likely will not sprout (I bought those once--the way the guy reacted when I told him they hadn't sprouted and asked him to check his source, I think he was just buying them from the grocery store and repackaging). Turmeric and ginger will sprout, but it may take as much as a year, particularly if the roots have gone dormant. If you got them from a grocery store they may have been treated to prevent sprouting, which doesn't actually prevent sprouting but does delay it. The first year it took 8 months for my ginger to sprout. 2nd year it took a couple of weeks. Turmeric sprouted more quickly because I think the roots were fresher, but still not fast the first time around. I wish I could find a decently priced vanilla orchid, but I'd probably just kill it. So I'm trying to grow one. :)

I bought the peppercorns from a tropical plant and seed supplier in Florida so I they should've been ok.  But they looked identical to the ones in my grinder so I planted 40 of them as well.  Two of their six coffee seeds sprouted and two of their 6 papayas sprouted.  

I should have said the ginger and turmeric I planted earlier this spring is starting to come up, just not the stuff in the main bed.  I got organic tubers from the store so I was hoping there weren't any inhibitors on them...

Oh, I got a really nice vanilla orchid from a local greenhouse.  They didn't have them on display but the pulled one from in back.  It had been 8' long but they wrapped it around a trellis.  It's getting used to its new home as we speak.  It was $29 so I considered it a pretty good deal.

And the two avocados arrived and are doing very well.

So I think what I learned is that I need to get the pile wetter when I build it.  I may need to add water during the composting season.  I think I need more N to get the pile hotter and to complete its composting by spring.  The wood chips seem to be small enough so I don't think I need to run them through my chipper.

I think I'll divide the chamber in half (E/W) and try a different recipe on each side.  One or both sides will get shredded hay mixed in to increase the Nitrogen ratio.  One or both sides may get a bunch of coffee grounds (20 to 50 gallons) to also bump the N.  One side may get run through my chipper to test smaller wood pieces.

Along with adding moisture to the pile there is also a high nitrogen category to get those temps up. Meat/meat broth, bone meal/blood meal, fish emulsion/hydrolysate, manures, green legumes, grains/seeds, hair/fur.
I like to use spent beer grains to heat things up and speed up the process. Making up about 10%-20% of your pile well mixed with everything else.
If I'm not using the material right away I dry it out as quick as I can by spreading on a tarp as thin as possible, preventing the party food to gas off.

(off topic)What was that brand of winter tires you suggested buying?

Thanks Robbie!  I've been avoiding manures due to not wanting the smells that would come from the process (methane and ammonia, I believe) since the pile is inside in my situation.  I was planning on drying the coffee grounds so they didn't mold while I waited to have enough for the pile.  If I get organic hay from a friend, that should count as dry and green.

Since I emptied the compost bin a week ago, the greenhouse has seemed to get colder at night.  Our late August weather has been colder than normal with lows in the 40s.  So I'm thinking that the slowly simmering 100-110 degree compost was providing more heat to the building than I was realizing.

(off topic for Robbie) They were Bridgestone Blizzak snow tires.

It's finally time for another update.  Summer and fall have been busy so not a ton of physical work has happened in the greenhouse.  

I put edge trim on outside of the south vent doors so that the missus could paint them.  They are now much prettier than before.  I installed the last three 8' glass doors under the water tower to act as an airlock for winter.  It still needs a few bits of wood but the hard part of putting the doors up is done.  Along with that I put a raised cinder block floor in the air lock to make the threshold level as you walk through.

We also put aluminum fascia on the south cinder block wall to cover the block holes.  I sealed it down with silicone since that was an air ingress location during the blower door test last winter.

Plant wise, I've cleaned out most of the south planting bed.  White flies had taken it over and their babies give off some honeydew or something that turns into a black mold.  The cherry tomatoes had climbed 10 feet up one of the curved trusses.  It was neat to see them intertwine and climb on their own.

The avocados arrived and are sitting in pots on the floor.  The mango flowered and set three fruit!  I trimmed them off since it's a puny little plant and didn't want it to waste energy on that.  Now it's putting out some more new growth.  After a long summer of inactivity, most or all of the citrus has pushed new growth.  The lemons flowered a month ago and set a little bit of fruit.  The ginger and turmeric I planted in the ground has all sprouted.  The two coffee trees that I thought were growing nicely are now sporting some nice bell peppers on them.  So I guess none of my coffee seeds sprouted and I just got some volunteer peppers instead.

Bananas are amazing plants!!!  They were 12" tall when I planted them on July 10th.  Three months later they are 7' tall and have stalks the size of my calves.

We had our first frost outside last night.  I'm starting to fill the compost bin with the fuel for this year.  I'm dividing the bin in half and doing a slightly different recipe on each side to hedge my bet.  Both sides will primarily be fresh wood chips.  Every half a cubic yard of wood chips, I add 3 gallons of coffee grounds, a shovel of char and 30 gallons of water.  On one half I also put in an arm load of garden clean up plant material.  My hope is that the added nitrogen from the coffee grounds and the added water (compared to last year) get the basic recipe cooking nicely.  And if it's not enough N, then the side with the garden clean-up stuff will do better.

Per some excellent feedback from a composting queen in the area, I am burying some 1" pvc pipes in the pile with holes in them.  That way I can insert water, high nitrogen water or air into different parts of the pile.  The pipes are horizontal in the pile for 4' and then angle up towards the access hatch.  I'll have two about 2' off the ground and two more at 4'.

I have the pile 1/3 built so far and hope to be done within a week.  Then it's on to:

Hooking up an inflation blower for the poly

Getting the moveable insulation working

Getting the heat storage ductwork, water tanks, thermostats and circulation pump installed and working

Automating all that so I can leave for a vacation in winter if needed

This is pretty ambitious! Nice work.

Nothing like approaching winter to get me back into the greenhouse!  About 5 days ago the compost was 140 degrees on the right side (garden scrap side) and 142 on the left side.  Today they had cooled off to 138 and 140 respectively.  I hadn't run the aeration fan yet so I turned it on for a couple hours and we'll see if that has an effect when I check again in a day or two.

I need to get the moveable insulation working and that required a bunch of steps to be completed.  Most are done now.  I had to open up the insulation chamber at the top of the greenhouse to unroll the insulation and get the weights fed back into the gap between the poly layers.  Wait, before that I had to install a hand rail so I can work up there more safely.  

So I pulled off the covers and fiddled with the weights yesterday.  Once they were all set, the insulation wouldn't slide down the channels due to moisture between the poly layers.  Ok, on to the fix for that... inflation fan.

I had previously installed an inflation fan to test if it could keep the layers from touching.  And it did.  So now I need to hook it up to outside air.  Why outside you ask?  Well, if I pump humid greenhouse air between the layers, it will condense and fill the gap with water.  Outside air is much dryer and "should" keep the air gap moisture free.  Thus the insulation should slide easier and not get frozen in place.

So today I cut a hole in the wall and put in a 4" duct hood and insulated line to the fan.  It doesn't look like much but it ate up 4 hours of my day.  Plugged it in and.....  it worked.  So now I'm going to let it run for a few days to dry out the poly air gap before I go back to tinkering with the moveable insulation.  

The greenhouse was 42 degrees inside this morning which is not great.  Of course it was going to freeze really hard for the first time last night so I pumped all our rain water into barrels and tanks inside the greenhouse.  So I cooled the greenhouse with about 900 gallons of 36 degree water that it now has to heat up.  

The whiteflies I've been battling are seeming to reduce in numbers.  I'm pinning it on the Delphastus Catalinae beetles I purchased to eat them.  The plants all seem to be dusty.  I'm not sure if it's dust or black mold or something else.  If there are any tropical greenhouse experts out there who'd want to help troubleshoot that, please let me know.

Blowing air between the layers did dry it out some, but it seems to still be wet.  I've been running the fan for an hour in the morning and evening around the time I move the insulation up or down.  The insulation comes up just fine but going down is another matter.  About half the time it works well.  The other half of the time I crank it down and 9 of the 10 move.  Then I go up to get them all moving and then back down and the same one is stuck.  Then up and down and a different one gets stuck.  After 10 up and downs and some jiggling of the poly, they go down.  So that part isn't ready for prime time yet.

We cleaned out the last of the garden compost and put about 2.5 yards of compost on the planting beds and mulched with some leaves.  

Then December hit (oh wait, it's early November).  And the compost heat stopped cooking.  I've been working on getting it going again.  Read more about that Here.  So it's getting kind of cold in there.  

It started getting below 10F outside at night a week ago and the interior temp started getting below 40F at dawn.  So several days ago I built a secondary greenhouse up on the compost platform and moved most of the pots up there to safety (space heater inside that enclosure).  The bananas and papayas are in the ground so our fingers are crossed.

Two nights ago it was 4F in the morning and today it was -1F.  The interior temp was 32 (per my crappy thermometer) but the bananas looked fine.  The papayas are "Mountain Papayas" and should be ok down to 18 degrees.

So, this greenhouse, with no working heat source, can keep the temperature 30 degrees warmer than outside on a cold winter night.  I guess in some parts of the world that would be awesome!  Too bad I need 55 degrees of difference...

The compost is starting to heat back up so there's a glimmer of hope that it will get warm before the next cold snap hits.

My next work will involve running wires and getting the electrical work up to snuff.  And figuring out a way to get the insulation moving better.  And setting up the heat battery system.

Here are some pictures before I moved everything upstairs.

You need to have a wood burning stove for maintenance and would spare you from pumping water into barrels in case of emergency.A Bullerjan stove would be great.
Also if you want frogs,they eat insects wich might be pests or good insects.
I will keep bumblebees all time in my greenhouse but frogs would eat them.To have a few native frogs sheltered its ok but to add tropical frogs i wouldnt.
Snake...if i add a snake then lots of people wouldnt visit my greenhouse because of it.
As for the bumblebees ,i will design a nice beehive for them ( wich amazingly i was thinking to make it sugi ban like but glazed with glass instead of oil) and i will catch the bumblebee queen from the wild and il explain everything in a forum here.
Il keep bumblebees non stop inside the freenhouse and il be releasing all the queens they make into the wild .
Somme plants like cherimoya still need hand pollination even if you have bumblees .
Get somme cherimoya trees ,they are subtropical ( minus 5 degree C) and they make the best fruit known to mankind / Mark Twain said that.
Otther nice fruit tree is the Achacha ,Garcinia humillis wich is a relative of the Mangosteen but much easyer to grow and more cold hardy.
Sugar apples are like small Cherimoya but more tropical than Cherimoya and too sweet ( cherimoya is a lot better) and they fruit from seed in 1,5 years.

Well I sure have been negligent in keeping this thread updated.  The plants are still hiding upstairs in their mini greenhouse.  I have lights on them and a space heater so they should be able to tolerate the winter.

The compost heated up to 135 with a bunch of effort (and liquid fertilizer).  Then, a week ago, I accidentally ran the aeration fan for 24 hours straight and the temperature crashed to 110.  Since then it's kept dropping and is in the 90s now.  So I'm getting the feeling that compost isn't going to be my heat solution.  It just seems too touchy to get it to work.  And I wasn't really getting any appreciable heat off of the bin even when it was at 135.

So last night it got down to -11F and my thermometer said it was 25 inside in the morning.  The bananas had made it through a 28 degree morning a week ago but this killed them.  The papayas have been seriously droopy for the last month so I'm hoping they're just going into a dormancy phase.  Or they're dead.  No biggie.

I have all the outlets wired so I don't have extension cords run everywhere any more.  Yay!

I haven't done much else due to other priorities and work.  I plan to get the moveable insulation motorized and to get the heat collection system working in January.  Or else!

@Mihai, you mention bumblebees, but you also talk about them similar to honey bees.  If you are thinking of keeping homey bees in the greenhouse, you might also want to consider setting up the base of the hive so that it can go outside, or inside, and that you can block either or both exits off.  The reason I suggest that is that you really do not want them flying around you and possibly getting hurt as you are also ripping up plants, tilling, and the like.  I'm trying to remember where I have seen hives designed like that.  As for bumblebees, the ones I have at my place as ground dwellers as far as I have been able to find.

Also, if you find information on setting up hives for bumblebees, please post here.  I have found very little research and engineering papers on native bee hives other than the Mason Bee (which can be made to nest in reeds and holes drilled into wood -- see https://thehoneybeeconservancy.org/2017/12/09/bee-hotels/ and other sources on bee hotels).  From what I've read, only 10% of the estimated 21,000 species of bees live in hives or communal structures.    Anyway, if you can pull together any papers, links, and information on species you work with or come across it would be a big help to the community.

Other than that, we all wish you the best of success.any

@Mike,  I am so sorry to hear about the demise of your bananas, and I hope your papayas make it.  

As for leaving the compost fan on, maybe we can help you find or design a simple circuit that would emergency cut power once it drops to a certain range, or monitors various details and sounds an alarm or sends you an email/SMS notifications.

As a side note, in my utility room, I purchased a simple heater that I hardwired and adjusted the temp down to about 40F.  I figure that if the rest or the HVAC fails, that this will keep the home-run plumbing manifold from freezing. Setting up a similar system in the greenhosue to turn on at a given set-point (like 34F) could possibly save them.

Also, 35F to 40F inside/outside differential in the middle of the night without an active heating system sounds impressive to me, and 55F is going to be hard to pull off without some help.  Have you thought about trenching a climate battery?  If you can trench about 10' deep, it is possible that you can be pulling in 40F air into the greenhouse (see https://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm for details), and if you have an additional closed loop, you might get  a bit higher. pumping daytime hot temps out the same tubes to warm up that soil as a thermal mass.  Just some thoughts...

if you havent already...
i would chop the bananas down to about a foot tall and the heap the wood chip mulch on there about a foot and a half deep

love following this project... keep trying with the compost heat!

Merry Christmas everyone!  I haven't chopped down the bananas yet but I should do that. Thanks M!  

I did dump the remaining liquid fertilizer that I had (3/8ths of a gallon) into three spots with about 4 gallons of water per spot.  So we'll see if that kicks it back up.  I also turned the air down to 5 minutes every day in case I was still giving it too much air.

So, based on last winter and part of this one so far, this design can keep a greenhouse above freezing inside as long as it rarely dips below 0F outside.  So while that isn't good enough for me, I bet there are lots of people who live in an area that doesn't get below 0F.  So, on their behalf, I'll call this a success and ready to roll out.  For those of us up north, I'll keep working on it.

I don't really see the compost working.  Or at least not in this implementation.  If someone had a horse or dairy operation with lots of fresh manure and the room outside to build a system, I'm sure it could work.  I'm just not seeing how to get an interior pile to work reliably enough.  So I'm redirecting my brain towards a wood fired system (batch rocket mass heater?) to handle nights below 0.

I did some work for an organic pastured egg farm, helped build a new barn.  The ceiling in those barns is a white tarp like material, about the same as the cheapest blue tarps and the rafters and purlins are on five foot centers, and they blow 18 inches of cellulose above that! To keep that tarp from sagging, they use green poly strapping like lumber bunks are secured with.  It is held in place with wide crown staples and pulled tight with a come along.  Something similar could help hold your poly up from snow load next time you need to replace it.

Thanks R, I know exactly what you mean!  There is a 1.5" gap between the layers so that should definitely do the trick.  Plus it would only need to be at the top 3' or so because the snow doesn't stay on there any farther down the slope than that.

Not much progress in the greenhouse over the past few weeks.  A local greenhouse manager came by yesterday and I picked his brains about whiteflies.  They're all over everything and the little beetles I bought to get rid of them didn't do the trick.  But apparently the flies aren't native to our area.  So if I can eliminate them, they shouldn't come back unless I bring new ones in with a new plant.  So there's a glimmer of hope.

I think the main body of the greenhouse will get cold enough to kill them.  The issue is in my temporary greenhouse where all the plants are hiding.  It's a balmy 55F in there.  So he's going to give me some yellow sticky traps which he thinks will clear them out.  I didn't realize the flies were attracted to the yellow of the traps.  So now I have hope.  If that doesn't do it, I'll get more beneficial bugs and let them loose in that small greenhouse to eat away.

Then I can hopefully plant more food and not worry about having white flies infest it and get it all moldy with their honeydew droppings.

Mike two quick questions.  I am going with plastic sheet now instead of polycarbonate,  Cost was way to much.

How is the 1.5" between sheets working?  I read you use a pump for a couple of hours for condensation.  Any advice?

Do you use a shade cloth in the summer?

\Thanks


.

The 1.5" between sheets works unless it gets really hot and sunny.  So if it gets up to 95F or so in the greenhouse (possibly the sun is the bigger factor?) the layers of poly get saggy and start to touch.  I had these layers "tight as a drum" when I installed them in the fall.  The blower will separate them just fine, especially on a normal greenhouse.  My insulation chamber has some leaks so the fan doesn't get to really build up a lot of back pressure.  

My condensation issues are, I believe, also from those leaks.  And from a long period 14 months ago when I didn't have the chamber closed off from the humid greenhouse interior.  

I haven't needed shade cloth, probably due to my latitude.  Having a tall greenhouse with decent sized vents allows for really good passive ventilation.  On my hottest day this past summer (90ish and full sun) the greenhouse didn't get over 105 inside.  Your results may vary if it gets over 90 degrees.  

Thanks so much for the info it is great.   Now that I am going with plastic my rafters do not have to as close.  I was looking at 3 to 4 apart.  Is 4 foot to far for the plastic?  yours look farther than that but you have the curve,  Main will go straight.  

Thanks
Doug

Mine are at 4' and I'm thinking that is just fine.  Especially if you don't have much snow to worry about.  One reason for the curve was so that if the wind got to blowing, the poly would still be held down to a surface.  If it's flat, the plastic could drum up and down and wear out prematurely.  Maybe.  I don't know but that was one thing that lead me to a curve.  If you have an inflation blower than it should mitigate that issue as well.

Snow can be an insulator.  All you really have to do for the coldest winter months is keep it from going below 35F.    And the folks at Biosphere in Arizona had real issues with their sealed greenhouse, so there may be some information there.

About the whiteflies, the traps are good, but as long as they keep laying eggs, then get caught on the traps, there will still be new ones being born.  There is an organic soap spray for whiteflies to spray where they could be laying eggs, in the mulch, in the potting soil of the other pots, since those things are not freezing.  White flies are also an indication of not enough air flow and stressed plants.  Since the goal is to not let it freeze in there, they are likely to manage to survive.  

You could cover up the most vulnerable plants with white agricultural fabric, or frost protection blankets if it's likely to go below 32F.

This might be of interest:


Do You Know How To Use Snow For Insulation?
survivopedia.com

There are air pockets which are trapped in the fresh snow that make it an outstanding insulator.

Now, if you’re the outdoors type, you probably noticed that wild animals and even stray dogs sometimes bury themselves in the snow when it’s freezing, and there’s a good reason for that.

Basically, they dig a hole in the snow and they manage to survive in that fashion even in -20 F temperatures. There are even species of animals that dig snow-burrows, where they hibernate for months, during the winter season. This obviously means that snow makes for an excellent insulator.

Also, you may be familiar with the concept of igloos. You know, those “houses” made of snow, or snow huts Inuit people are often associated with. Besides igloos, Inuit people used snow on a daily basis to insulate their whalebone/hide-made shelters. What makes snow such a good insulator?


Why Is the Snow Working for Insulation?

To get an idea, even if the outside temperatures are as low as 19 degrees Fahrenheit, in a snow hut you can achieve 61 degrees Fahrenheit using body heat alone, provided we’re talking about a burrow, not a palace; i.e. a small fox-hole, large enough to fit you, so it can be heated sufficiently by body temperature alone.

The best snow in terms of insulation is fresh snow, because it contains a high percentage of air caught between the ice crystals. Fresh snow is basically all air, up to 95%, and that’s why it’s so light. Since the air is firmly trapped inside and it cannot move freely, the heat transfer is significantly reduced.

That brings us to the next factoid: did you know that 10 inches of fresh snow, which is basically five to seven percent water, is the equivalent of a 6 inch layer of fiberglass insulation? That makes for an R-value of 18.

Snow’s thermal conductivity, which is the scientific term that describes that R-value thing, can be described mathematically and it works in tandem with the snow density. The denser the snow, the greater thermal conductivity. So, if you want to use snow for insulation purposes, the best snow is the fresh driven/super-light-fluffy snow, as heat moves through it relatively slowly.

Back in the day by the common folk for insulation purposes,  those living on farms used to drive six foot posts into the ground about 3 feet from the sides of the house, right before winter set in. After that, they used to pile straw between the house walls and the respective posts. After the first big snow, they packed the snow over the straw, creating something resembling a wall of ice.

That insulating wall stayed there until the spring, when it melted away. This ingenious yet primitive makeshift insulation really performed miracles, by keeping the winter cold out and the heat inside the house.


How to Make It Work

An  idea for putting the wintery blanket to good use would be to let it sit on your roof, depending on how solid the roof is built. If it’s built properly, a layer of snow will provide you with additional insulation, for free, but in case of heavy snow-fall, make sure you don’t allow more than two feet of snow to accumulate there.

Too much snow on your roof may translate into leaks, it may damage your roof when it slides off, or it may even collapse the roof.  Snow accumulating in decent amounts on your roof, without melting in certain unusual spots, is a testimony that your attic is doing its job, meaning there’s no heat loss through the roof, due to poor insulation.

A properly insulated home doesn’t show bare patches of melted snow on the roof. Hence, beside its insulation advantages, snow will act as an early warning system.

Thanks Cristo!  The snow info doesn't really help my greenhouse since the roof it pitched enough to shed it.  The pile along the base of the south and north walls are likely helping me out though.  Might be worth reposting in its own thread in case it helps folks in other situations?

For the white flies, the greenhouse guy, and several online sources, say they lay their eggs on the underside of living leaves.  So I think if it gets cold enough in the greenhouse, the cold should get to them.  I'm just not sure how cold it needs to get.  It hit 25F once so far but near the ground it was probably warmer.  I can open the doors and get it plenty cold if needed.

If anyone knows the temperature at which white fly eggs die, please let me know!

any updates?  How are you faring the pandemic?

Thanks Ebo, I've been delinquent in updating this.  The greenhouse made it through the winter just fine.  The compost didn't provide any heat from mid or early winter onward.  The coldest it got outside this year was a balmy -22 and the coldest it got inside was +22.  The bananas died when it got a couple degrees below freezing.  I was surprised at how tough they were.  When it got below zero outside, it tended to break below freezing inside.

So without any appreciable heat, this greenhouse does pretty darn well in a frigid, cloudy climate.  I'm sure if it was located in zone 6 or somewhere sunnier, it would stay above freezing all winter without any heat.

Unfortunately I have clouds about 2/3rds of the time in November and December and about 1/3 to half the time for Jan and Feb.  So I'm investigating adding a batch box rocket mass heater over the summer.

The whiteflies appear to be gone (fingers crossed).  So either the cold or the yellow sticky traps I put out did the trick.  I bought a 100 pack of the yellow traps so I can just keep them around and the white flies seems to be magnetically drawn to them.  As do the fungus gnats.

I planted cabbage starts in the greenhouse late last summer and they overwintered just fine (growing a bit) and I just ate the first few this week.  The seed packet let me down and they were actually cauliflowers.  One volunteer pea is 18 tall and I should've planted more earlier, but the pea patch is now all sprouted.  I have lettuce that have just sprouted and some carrots and chard seeds in the ground.  All this is in the annual planting bed along the south wall.  I'm starting the garden seedlings as well.

I have a dozen jicama seeds planted, we'll see if they sprout.  All the potted plants made it through the winter in a temporary greenhouse up on the yoga platform.  I'll bring them down this weekend and start potting them up a size.

I'll post more pics soon...

If you are getting 40F to 45F inside/outside differential is respectable.  Congrats on the first year!

As I recall, you have it pretty well instrumented, correct?  One experiment would be to get a 100W heat lamp (or McGiver one out of a couple of coffee cans and a light bulb).  Do that for a couple of cold nights, or put in a 1KW space heater overnight, and see how much of a difference that makes.  If your greenhouse is not leaky, then you might be surprised at just how much a little heater will do for you.  A rocket stove could easily fix the problem as well, and is a much more sustainable solution.  Personally, I would still run the experiment to get a sense for what a smallish (say 1 or 2 KW heater would for the min temp), and then plan to have something like that as an automated emergency backup if/when something clogs the stove, and it goes out 15 minutes after you go to bed.  Also, have you ever thought of setting up a temp warning alarm into your house?  Just a thought.

Thanks Ebo!  That's a great idea!  I wish I'd've thought of it a month ago when it was colder.  I'm not sure I'd get a good read on the situation now.  A bit more sun really changes the temps inside whereas when it's 0F outside, the temp inside is pretty regular.

I have debated a backup heat system.  When I was counting on compost it didn't seem necessary.  Now that I'll be on wood, it seems a bit more reasonable.  I'd be pretty tempted if someone had a pellet stove they were giving away.

I moved the potted plants down from their winter exile and potted some of them up.

I've been very impressed by this project and really enjoyed watching it. Thanks for sharing with us all as you work on this!

As far as bananas go... have you ever heard of the Ice Cream Banana Tree? Sometimes called the Blue Java Banana. I haven't grown it but from what I've read about it from multiple sites it's supposed to have a great flavor but also be very cold hardy--all the way down to 20 degrees F. Multiple sites list it as being able to survive winters in zone 8.

I have a long term project to create a warm micro-climate on my property to jump things to zone 9 and I want to try growing this banana outside in that spot. I have no clue if it will survive or ever produce fruit even if it does but I thought it would be a fun challenge. Fresh bananas from western WA would be a fun thing to have! If the banana can survive zone 8 winters then pushing things to zone 9 should work... but the growing season may just be too short here.

But in your green house an extra hardy banana like that one might just do great. Here are some links talking about it:

https://en.wikipedia.org/wiki/Blue_Java_banana

https://www.fast-growing-trees.com/products/Ice-Cream-Banana-Tree

Thanks for the idea Daron!  If the new ones I got this year don't make it, I'll give that a shot.  

The seedlings in the greenhouse are doing fairly well.  Biggest issue is aphids on the peppers and sweet potatoes.  The citrus is doing quite well and has been flowering lightly but consistently since mid March.  Looks like I'll have some lemons, key limes, mandarins, Australian finger limes and calamodin oranges this year (if all goes well).

Bananas and a passionfruit are in the ground.  The bananas have been slow to get going compared to last year.  The passion fruit started slow with some aphid attention but now it's starting to win the battle.

I have a double row of peas in the south planting bed that are just starting to have pickable pods.  I could've planted them a month or two earlier.

I will probably empty the compost bin this week.  Then I'll figure out how to demolish the bin and platform above it.  No more compost in this greenhouse!