Backyard Aquaponics
A place to discuss aquaponics

What is the coldest a green house can get over night without harming most plants. We got down to 26F/-3C outside air temp, my green house got down to 43F/6C. Can the plants put up with these temps? I have tomatoes, celery, lettuce, cabbage, Brussels sprouts, and things like that.

I imagine up to the point of freezing, once that happens they're toast (most plants). I was reading about "biologic zero" which is 41 where soil activity ceases, I think you'd need to stay above that to keep anything worthwhile happening.

Thanks water temp so far is staying up above 60F, so root temp should be about the same I think. If water temp gets to 40 all my fish will die.

I can see differences in my tomato varieties as the temperature drops. I have some yellow tomatoes that are definitely looking worse for wear, but some heirlooms that are thriving. The lettuces, radishes, and various brassicas are holding up well.

Basil hates low temps. Most of your warm weather vegetables won't do well but will survive, like tomatoes, peppers and eggplant (it varies as mentioned, I've had good luck with mini bell peppers but they have to be established going into the cold weather). The main thing to be certain of is that you have good air movement so that you don't get condensation dripping down onto the plants. There's a good book called The Polytunnel Book - http://www.amazon.com/The-Polytunnel-Book-Fruit-Vegetables/dp/0711231702 - I'd take a look at your library to see if it's of use to you (It's written with England in mind and much of this applies to the Pacific Northwest, where I am, but might not be as useful for you)

Cheers

What is wrong with condensation dripping?

Condensation from the ceiling is much colder than the air in the greenhouse and it works about the same as water from the AP splashing up on the leaves - ceiling condensation dripping down and what condenses directly on leaf surfaces encourage disease.

I found that by planting in polystyrene boxes with a good layer of mulch on top seems to help, with the temps you are talking about you are not looking to protect from frost.

Huh, so how do you stop that and not defeat the purpose of the green house to keep your temp stable? If I let air in then my temps will drop.

This is just our first cold front. We have at least 3 more months of winter. The lowest temp I have seen here is 10F/-12C. I need to protect them from those types of temps. We have had a week where the temp never got above freezing with most nights going into the teens.

Well in that case, you might have to grow a winter crop. How do you feel about turnips?

From what I can gather things exposed to the cold air will suffer but things in the ground will stay slightly warmer.

You might have to try cropping something else. My peppers would die off in the UK over winter but in Australia they are perenials.

A quick list I googled
http://www.greenhousecatalog.com/winter-garden-crops

Consider trying these vegetables in your cold-weather greenhouse:

•Beets
•Broccoli
•Brussels Sprouts
•Cabbage
•Carrots
•Cauliflower
•Celery
•Cilantro
•Fava Beans
•Garlic
•Kale
•Lettuce
•Parsley
•Radish
•Spinach
•Swiss Chard
•Turnips
Also some advice from the same site re: ventilation

Even though temperatures are cooler in the winter, plants still need some ventilation in order to stay healthy. The greenhouse will need some gas exchange so that the plants have fresh carbon dioxide and can properly photosynthesize. Some gentle air flow also keeps pests away and will encourage sturdier stem growth.

You can stop the majority of condensation issues by installing a circulating fan to move the air around in the greenhouse (I let this run 24/7). The size of the fan/fans, depends on the size of the greenhouse. I use a dinky 6" oscillating fan for the little 6 X 8 harbor freight greenhouse I'm using at the moment.

As far as venting goes, Jizlizard is correct but you can get away with sealing up the greenhouse for some of the coldest periods. Keep in mind that on a sunny day in Winter the temp inside your greenhouse will still get up to 85 (where you are anyway )so you should be able to bring in fresh air when the sun is shining - Try to do it early enough the fresh air can warm before nightfall but not so early that the greenhouse hasn't warmed up some already.

Commercial greenhouses often use CO2 generators instead of losing the heat.

I've seen plans for a heat exchanger on the BuildItSolar website (don't know if it would be of any use for a greenhouse but I thought I'd mention it anyway).

Current sump tank water temperature is 48 degrees F with outdoor highs in the 40's and lows getting down into the upper 30's at night. My system is half in a greenhouse and half outside. I have no heating in the greenhouse at the moment and haven't seen the sun much for 3 weeks so solar isn't really helping much. Now you know why I'm not trying to grow Tilapia

Cheers

Thanks I am going to put a fan inside of it. Today our outside high was about 37F/2.7C, and the green house got to 90F/32C. When it gets above 80F I open up the front of the greenhouse which is on the south side. So on most days the greenhouse gets opened up unless it is very cold and there is no sun to heat it up. My wife is going to check the water temp and will let me know shortly.

Thanks after seeing the list you posted I have a bit of that planted already. Have lots of lettuce and cabbage, and some celery.

Here is a celery bottom, after we removed all the stalks, I planted the base of it in my grow bed. This pic was taken 5 days after I pulled it out my refrigerator and planted it.