Indoor plants - screen porch in winter

Hey everyone.

I think I mentioned this here sometime, and I've been thinking of it for the six years or so since I moved here.

We finally did it, though in a somewhat makeshift way. I figured if it worked well, I'd make a more permanent fixture. And after more reading and experimentation I realize there are LOTS of factors. It may need tweaking. But my few days' experience is SO promising, I wanted to tell you all about it.

I live in northwest Florida, which we get freezes down to about 27-28 F some few nights, around 32-36 quite a few nights, and warmer periods alternating. Days can range anywhere from 38-70 F - sometimes colder or hotter, through the winter. So it's a really unpredictable climate, but overall usually too cold for houseplants outside.

This addresses food plants too.

So what we did, is we have a screen room which has a concrete floor on a raised slab, sharing one brick/siding wall with the house. It gets sun from south and west most of the day. We put up pretty thick plastic (not clear - I have wondered what difference that would make since I'd rather see out, but otoh this kind diffuses the light - at any rate it's what we had on hand). It's sealed with caulking at the top and along seams. The plan was to seal it at the bottom too but it was wet - given how it's working out we aren't going to. Instead it just folds in a few inches and bricks hold it down. That means it can be vented a few inches though.

So here's how it went. We had three nights below freezing. The plants all out there (except one or two I was afraid to risk). I have a very small ceramic heater that uses little power on low setting. The heater running through the night kept the porch around 55F. I was concerned about power costs though it will not be many nights a year. But here's the really cool thing! As soon as the sun comes up the room starts to heat, and by 10am it was 90F! So I turned off the house heat, opened the door to the porch, and the house stayed toasty all day without running the heat! So I think a tiny heater running some hours at night a few nights here and there is going to cost much less than I was spending on central heat for the whole house!

With the porch open to the house, it cooled to around 75F out there. And it retains a degree of humidity. I think the plants are going to do MUCH better out there than almost anything else I've ever done with them over winter - they tend to suffer with reduced light and humidity no matter what I do, and I wear myself out moving them in-out-in-out with our capricious weather.

We have peppers and lemongrass out there too since they were still growing. The peppers look like they might produce really well out there. I need to research temp requirements for different veggies/fruit, but it may be that we can grow in the winter out there.

I'm really pleased. The only thing I need to discover is how much the heat is going to be a factor for days when I'm working and can't move the air into the house. I need to discover how much to vent, whether the ceiling fan helps, or if I need to pull down shades. But school is closed for a week (good timing) so hopefully with 9 days to monitor and experiment I'll be able to discover how to safely set it up while I'm gone.


If all goes well, next year I plan to build frames of wood for the plastic, and a means of attaching it to the porch frame so it is easily removed for venting, etc. And a rack on the garage ceiling to store them. With the amount of exposure/use they get, I think they will last 2-3 years before needing to be rebuilt.

I'm pretty excited about the possibilities. And initially I was just SO glad at the prospect of not having to move them all over and over (not to mention having them languish inside for days during a cold snap, all in my way and dropping leaf litter, etc).

I'm seriously wondering if I can grow strawberries and tomatoes out there too.

I'm also interested in a double layer of plastic with an air space between. I can't really do it with the current setup, but with a frame it would be possible. It would provide more insulation in colder climates. Might not be necessary here.

I was initially interested in various models I've seen for creating a "heater" using various setups with bricks, cinderblocks, etc. as a sort of passive reservoir for the heat, produced by candles or a can of stereo. I can get a lot of beeswax (though I'm more interested to use it for other things than heating). But I get so much conflicting info I wasn't willing to chance it at first. I'll probably experiment later.

Also some use large barrels filled with water as heat reservoirs to absorb daytime heat and release it at night. (Hydroponics for some.)

Actually one very cool idea I read - NOT for a screen porch lol, but an actual detached greenhouse - is a trench with compost running the center that actually produces enough heat to warm the greenhouse, and of course compost. But my compost heap is FAR from my porch lol, and staying there. Though I wonder if there's not some potential use for that heat I could be missing. Can't really imagine what for though. Maybe run a worm bed alongside of it ... but worms do ok below soil level here anyway.