Tiny greenhouse ground insulation help! (Northern Ontario)

I need some help... we have a tiny polycarbonate greenhouse (6x8') from a kit and I'm planning to try to winterize it to extend my season on some cold weather crops (everything in pots and grow bags), and protect some other plants for the winter. I'm in zone 4a, so winter is coming awfully soon  (we have a high of 9c expected today!)

I have clear bubblewrap to insulate the south side, and reflective bubblewrap for the rest. I have a string of incandescent outdoor lights to add a bit of heat when needed, and a water barrel for thermal mass. (as soon as i figure out how to get it in as its JUST wider than the doorway). I have an actual space heater as a backup to all of this, plugged into a temperature sensor, but don't plan to run it except in dire emergencies.

This place is not a permanent location for us...probably one or 2 more years at most.

Now for the crux... it has no flooring as of yet, and it has a low spot in the middle. I don't have the capacity at the moment to build a proper floor this fall, and anything i do needs to be removable. What i have right now is a couple of (black) outdoor carpets for weed suppression. There are also gaps along the bottom of the walls (we levelled and supported the corners,  built a wood frame, etc.)

I have some metal meshing to keep rodents out of the gaps, but i need to figure out cheap and easy ways to stop the air flow under there, and possibly insulate the ground a bit.

Any suggestions? TIA.

Bear with me Mel! This might sound weird at first! I would put down reflective, bubble wrap insulation on the ground for 3 ft or more around the outside of your green house.

This method - although usually put in slanting into the ground starting at near ground level and going deeper further out - is like an umbrella holding the ground's natural heat in. It has been used to insulate uninsulated houses in places, although I saw the diagrams years ago and haven't a clue where at this point (more than a decade likely).

The biggest problem I've read about with a small greenhouse is the fluctuation of the temperature - too hot when the sun's out, too cold when it's not. Insulating the floor will reduce the thermal mass, and yes, a water barrel may help, but the ground is your biggest, cheapest thermal mass source, so the question is, can you capitalize on it?  I'd also welcome the snow on top of the ground insulation, as it provides some insulation also.

That's an interesting idea, but unfortunately i have 4 large dogs who would DEFINITELY shred anything like that outside the greenhouse! Also, since the greenhouse is so small, there is a 100% chance that the ground will be very very frozen by December. Once we are in a more permanent location,  i have big plans to dig down and insulate a perimeter (of a bigger greenhouse) so we can use the ground as a thermal mass, but i can't see that there will be anything but heat loss in our current setup.

(thank you for the idea though, filing it away in my future plans folder!)

Well the gent managed to scrounge up some wood,  so I'm getting a floor after all!

In addition to the straw under the floor, I would like to suggest some star bales on the perimeter walls either inside or outside.  Maybe three or four feet high.

That is a nice set up that you have.

Anne Miller wrote:In addition to the straw under the floor, I would like to suggest some star bales on the perimeter walls either inside or outside.  Maybe three or four feet high.

That is a nice set up that you have.

thanks! I'm putting a low (12") raised bed on the south side (planting garlic there) so I'll have the soil in that for insulation, but additional bales on the the outside is a good plan!  (If I put them inside, I'd have no room for plants lol!)

How are you going to make sure the straw in the floor doesn't get wet and then moldy?

Jay Angler wrote:How are you going to make sure the straw in the floor doesn't get wet and then moldy?

I'm hoping the tarp underneath with help with that; it is about 24" oversized on each side so it's tucked up and over the edges; it's not the low spot in the yard, so it should not have standing water under it; just rain runoff until we get snow.  If we start to smell it getting funky, we will probably retire it for the season and try something new in the spring (we are using things I already had on hand for the most part, so the straw bale was already here. As much as it would be fantastic to be able to use it all winter, it's definitely an experiment this year, so I'm not going to be devastated if things don't work out, otherwise the straw will get removed in the spring either way!

Mel, I'm more concerned with moisture *inside* the greenhouse going through the floorboards and collecting down there.

Did you use nails or screws to hold the floorboards down? Maybe leave some boards unfastened in spots for checking and potentially sopping up accumulated moisture?

Jay Angler wrote:Mel, I'm more concerned with moisture *inside* the greenhouse going through the floorboards and collecting down there.

Did you use nails or screws to hold the floorboards down? Maybe leave some boards unfastened in spots for checking and potentially sopping up accumulated moisture?

Ah! That's a good point... we are using deck screws to secure the floorboards, but leaving at least one loose board is a good idea! On the up side, if it's just condensation on the walls, that will land in the channels at the bottom of the walls, and should not end up in the straw.  

Mel Wilde wrote: On the up side, if it's just condensation on the walls, that will land in the channels at the bottom of the walls, and should not end up in the straw.  

But if you have plants, they will need to be watered and it will only take one accident to dump a whole watering can! Or simply to overflow a pot. I always like to plan for fate to get me, and then be pleasantly surprised when it doesn't!

Jay Angler wrote:

Mel Wilde wrote: On the up side, if it's just condensation on the walls, that will land in the channels at the bottom of the walls, and should not end up in the straw.  

But if you have plants, they will need to be watered and it will only take one accident to dump a whole watering can! Or simply to overflow a pot. I always like to plan for fate to get me, and then be pleasantly surprised when it doesn't!

We were just discussing that!  I have a rubber-backed carpet that I'll put under the pots to catch slight overflow issues... i am hoping that as long as we allow for evaporation,  it'll be ok... the air is quite dry in winter!

Mel Wilde wrote:... it'll be ok... the air is quite dry in winter!

Right! I should know that, as I used to live in Ontario, but after 25 years of living in the Pacific North Wet Coast area, I forget that you guys are known to run humidifiers in the winter! It took me years to convince my Ontario born and raised spouse that we need to run dehumidifiers in the winter. 80% humidity in the bedroom feels like trying sleep in cave!