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Greenhouses & Garden Structures

Cold frame within greenhouse?

staceyandersonrn

7 years ago

Hi! I've been searching the internet to try to find out if a cold frame in a greenhouse would get hot too easily. I have a little 6x8 polycarbonate greenhouse that we just put up, and right now I have some seedlings on seed starting mats on a table in there. I don't want to heat the whole greenhouse on cold days and i was thinking of just building a clear polycarbonate housing on the table with a mini heater on a thermocube inside. That way I could keep the seedlings warm without hearing the whole greenhouse. I might get not even need a heater, the heating mats might do the trick. I could open the front of it for circulation....

Thanks in advance, for any advice you can offer.

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Comments (5)

eciton
7 years ago
the answer is it depends.

it really depends on the amount of light you received, the temperature outside and the ability to ventilate your greenhouse. plenty of people do exactly what you are doing for seedlings or other items that are extremely cold sensitive.

i would recommend you make sure the cold frame gets a good amount of air exchange daily to mitigate mold issues
staceyandersonrn
Original Author
7 years ago
Thank you so much for answering. We're building it, hope it works well!
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Winter is over, it's early spring i'm worried about. Your greenhouse appears to be polycarbonate. Mine is 6 mil plastic. I just came in as it has turned cloudy. 50 degrees outside the greenhouse 59 within. It's not completely closed up. I need to tape, patch holes and sorta seal the base from drafts. Definitely not an ideal structure. i'm about as early as you can get because these plants were started about 1 year ago. They are the suckered growth of a suckered tomato plant but i consider them to be 1 year old or more. I have got away with a 6 month old tomato plant(same variety)I had grown in the house on Halloween because that year late blight wiped out everything. I wrapped it up in heavy row cover and set it outside April 1st. It got a bit frost bitten. That was 2 or 3 years ago. Last year I tried to get an early jump in March and the tomatoes all died. They were set in the ground though. no double greenhouse just a single one.
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The main problem with sensative crops like tomatoes is that you will need to constantly monitor temperatures in a smaller enclosure. One month gain in starting is a more realistic under most conditions and then you would be best to germinate tomato seeds indoors at much higher (80-85F) temperatures before placing seedlings in the frame. A few thimgs that are useful for a smaller unit: For an aid with heat a light bulb or string of Christmas lights may make a big difference on cooler nights. For daytime a hinged cover that can be propped at various heights is helpful. If you have an old waterbed or swimming pool bladder you can lay it inside and partially fill it to buffer the heat extremes. A thermometer laid inside will be helpful during your frequent evening and early morning visits when you have the unit tightly closed. Cold Frames tend to work best for hardier crops like cole crops or onions. But if that is what you have available you can easily make it work for almost any crop. Years ago they were the plant starting structure of choice for most home gardeners.
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chadinlg Zone 9b Los Gatos CA
7 years ago
I had a setup very much like this and it worked very well. I had heating cables in the ground under the pots of the 'cold frame', I also had a 'instavent' vent opener so I would not need to remember to open the frame on hot days. A small fan inside the frame as well.
staceyandersonrn
Original Author
7 years ago
I was thinking about an instavent too. Now I will definitely have to try it. Thank you! Oh and the fan of course
PRO
Advance Greenhouses
5 years ago
There are a lot of people who do not heat their greenhouses in the winter. I have discussed the options in this blog post.

https://www.blog.advancegreenhouses.com/the-winter-greenhouse-heat-or-not-to-heat/

One of the options is to "dress in layers" just like Mom taught us. The cold frames are a great idea, but you will need to monitor them at first to see just how the temperature is reading. I would get a max/ min thermometer and put it in the cold frame. That will help you to get a clear picture of what is going on in a hurry. Tammy

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