insulated, windowless barn for overwintering dormant plants?

11 years ago

I'm brainstorming here. I've been thinking about starting a "backyard nursery" to grow trees for resale in containers. Since our winters are cold, overwintering outdoors in pots is diffcult unless you:

1. Mulch up all around them
2. Do a "pot in pot" system, which requires drainage, labor, etc, etc
3. Move them to some structure in winter to keep just above freezing.

While I am not sure whether the two-time HEAVY labor needs of moving several dozen to a couple hundred 1 to 10 foot trees is less than mulching them up, it seems worth considering this option:

I don't need a "greenhouse" as this would solely be for the purpose of keeping deciduous dormant plants dormant, but not frozen to protect the roots. I already have a well built wood pole barn 40' X 30', that was here when I bought the place, has a concrete floor, drainage, electricity, and a spigot. I could put up R38 insulation on all side walls and roof, it would fit, but currently it's unheated and uninsulated, but it IS sealed rather well (I'd put in a better-sealed door on each side).

Right now I only use about 1/4 of the floor area for things like equipment, mower, etc...so my thought was, why not insulate it and heat it just to maybe 35 degrees and use it to move the container trees into once they go dormant, then yank them back out in spring?

Although on the surface, mulching seems "easier" - the labor involved with getting large quantities of mulch and then cleaning it up seems more or less equal to moving them into a climate controlled location, where winds, ice, snow, etc. are less likely to be a problem...I dunno.

If I were do to this:

1. Since it will be a fully insulated, windowless structure, how do I calculate BTU needs for heat?

2. With no direct light inside, would there be any chance of getting TOO warm on sunny, warmish days to where early breaking of dormancy could be a problem? If so, would a ventilation system like a greenhouse would have be worthwhile, or would the heat loss from fans and shutters override the benefit?

3. Would it possibly work to just heat the concrete floor, since it would radiate upward into the containers? The tops of these trees would all be fully hardy in my zone, it's just the roots I want to keep above ambient temps. If this setup were possible, how would I calculate if the heat could move "up" far enough into the containers to do what I need it to?

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Comments (4)

cole_robbie
11 years ago
Ohio requires a nursery license. You would want to contact the state first and ask if there are requirements in regard to your structure.

As far as your idea goes, your heating costs would depend a lot upon how cold the winter happened to be. You might consider a wood-burning stove if possible. The link below will let you calculate your heat requirements in BTUs, but it all depends upon the outside temperature.

Here is a link that might be useful: Heat Loss Calculator
joeschmoe80
Original Author
9 years ago
Bumping this old thread since I posted a related thread.

I like the idea of walling off a small room and heating just that.

Has anyone determined the "too warm" question?

In other words, if I overwinter plants in this insulated room (say 10 X 10, smaller than the whole barn...and heat it to just 32 degrees...do I run the risk of it warming up too much and plants breaking dormancy? I mean, if we have a sunny winter day of 55 degrees, and the weather has been cold up to that point, is this insulated structure (with no windows) likely to be warmer, or colder than outside at that time? I would almost think that if it's well insulated, it might actually be COLDER than outside in such a situation.
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fruitnut Z7 4500ft SW TX
9 years ago
Insulated to R38 you shouldn't have to heat much if air tight. You don't need to hold above freezing. I'd be thinking above 24F. By allowing it to drop lower in cold weather your worries about warm weather decrease.

And yes it will be colder in there on a warm day than outside. If you go with the big water storage tank all the better. That would moderate temperature immensely. I'd think the swing day to night should be less than 10F even without water.

If pots are setting on a concrete floor cover with insulation. The ground heat from concrete would keep pots from freezing in that structure.

This post was edited by fruitnut on Fri, Dec 19, 14 at 14:03
hairmetal4ever
9 years ago
My gut says that such a structure would, in an unheated state, probably have daily average temps not too far removed from outdoors, but with less day/night variation.

Example - in January, if you have an average high of 35 (I'm guessing for Ohio) and an average low of 21, that's a daily average of 28. Inside your structure it might be more like a high of 30 and low of 26. To the point where if you set a thermostat at 24F as fruitnut suggested, the heat may run only rarely and on very cold nights (low teens or colder).

But, as fruitnut said, if you had a sunny 60 degree day and it's already cold inside, I don't think it would warm up to 60 inside. Maybe the 40s if there are no windows.