Built a small greenhouse and have some questions

mozzlesMay 13, 2012

I'm new to gardening and am growing some vegetables in containers this year, living in central Oregon I know we have a very short growing season, so I was originally leaving all my plants inside at night, and bringing them outside during the day.

I've got 7 different 5-6 gallon pots with tomatoes, strawberries, bell peppers, and one pot with two hot pepper plants. So after awhile, I got tired of having to move them constantly, and also needed more room. My solution was to build a small greenhouse, my dad helped me with it the other day while he was visiting. Was pretty basic construction, we used wooden stakes from a garden store and 6 mil plastic sheets.

It came out pretty good I think, today it's only been around 80 degrees but I last read about 102 degrees inside the greenhouse. I do have some questions since I've never done this before.. how much does a greenhouse of this size need to be vented? It's pretty humid in there and I've had the door of it open all day, but am fairly sure it will need some other sort of ventilation. Should I cut a hole in the plastic on the opposite side of the door, to make a window?

Another question I have is whether laying the plastic sheet on the ground like I do is good, or if I should do something else. I didn't think it'd be a good idea to set them directly on the ground, but one thing I thought of is whether having that plastic would prevent the ground's heat getting into the greenhouse like I'd want it to at night. We have very cold nights where I live up until later in the summer.

Any recommendations you all have would be appreciated. I am trying to think of an idea to put a trellis inside so that when I transplant my kentucky wonder pole beans they will have something to grow on. Also of course my tomatoes will need something to grow on as well, should I get a tomato cage for each pot or use some kind of trellis for them as well?

Here's some pictures I took today of the set up.



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fruitnut Z7 4500ft SW TX


You should be able to ventilate that well enough just by opening one side better. This will cool things off down at floor level pretty well.

Now for the bad news. A shelter of that kind won't warm things up at night very much no matter what you do with the flooring. Some water mass would add a couple degrees at most. The only thing that will really warm it up at night is a heater.

    Bookmark   May 13, 2012 at 11:38PM
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I don't have any outside power outlets, would it be safe to use one of those no exhaust propane heaters in something as small as this?

Another thing I had read about was painting plastic or metal drums black and filling with water. Do you think that would work for my greenhouse?

Thanks for your advice about the ventilation.

    Bookmark   May 14, 2012 at 12:42AM
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fruitnut Z7 4500ft SW TX


I'm very wary of any combustion heater that isn't vented outside. In something that small it might be OK if you ventilate well before entering.

Black drums full of water will help some but without insulation at night still not that much.

Things will grow faster this summer inside than out just because days will be warmer.

    Bookmark   May 14, 2012 at 4:52PM
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Then would you have any recommendations? Keeping all of my plants inside all summer is not an option, I don't have the space. I've read that sheets of styrofoam put in at night can help a lot, do you have any experience with this?

    Bookmark   May 14, 2012 at 6:53PM
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I've just realized that you were probably suggesting that things will grow faster inside my greenhouse than outside, and not inside my house like I originally thought you meant. In that case, I hope so! What would you recommend for any cold nights? There are supposed to be 2 or 3 nights under freezing in the next couple weeks where I live, according to the current forecast.

    Bookmark   May 14, 2012 at 8:30PM
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karin_mt(4 MT)

Hi Mozzles,

I bet you can get your plants through the cold nights by putting blankets over them. When I do this I stick a bamboo stake in each pot and then drape a blanket over the whole thing. That way the blanket does not crush the plant. If you have a decently thick blanket the plants will be OK if it's a few degrees below freezing.

I'd also go ahead with some water buckets. It will help a little and it's so easy. But overall I bet you'll have fine results because it will be warm during the day. I made a plastic covered hoophouse last year and our pepper plants loved it in there!

    Bookmark   May 15, 2012 at 1:14AM
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Thanks Karin.. I've been getting so worried since seeing the forecast where I live. I'll look into the blanket thing, would you recommend like quilts, thin blankets.. which kind? I'll go to the thrift store today and see what I can find. Also bamboo stakes.

    Bookmark   May 15, 2012 at 10:26AM
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karin_mt(4 MT)

Any kind of blanket will do - especially on the cheap! Something not terribly heavy but still cozy and insulated. I use fabric from JoAnn's that is made from recycled bottles. But anything will do!

    Bookmark   May 15, 2012 at 6:14PM
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Hey that sounds nice, I'll go to JoAnn's and take a look. Is it very expensive?

I talked to a local gardener earlier today and he said here in a few weeks we should be frost-free so I don't have much longer to worry. Though where I live there's a chance of frost in every month I believe.

    Bookmark   May 15, 2012 at 10:57PM
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karin_mt(4 MT)

I think it was something like $6 per yard? It's in the part of the store that has fleece. It's white. I like it because I am usually covering rows and the shape works well for that because you can buy nice long pieces. But the thrift store is likely to be more economical.

Nowadays I keep the blankets folded up on the greenhouse shelf as they are not needed much. The kitties are in heaven curled up on the cozy pile of blankets in the sunshine. So there you have it - dual purpose frost blankets. :)

    Bookmark   May 16, 2012 at 1:05AM
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