Heated planter/greenhouse idea (growing, vegetable, south, frost)

[poncho62]

I would like to get some opinions on an idea I have.
I want to convert one of my planters I built into a small greenhouse that I can have my seedlings in while growing.
I have a heated cord used for keeping ice build up off the roof edge of the house. It is low wattage, so shouldn't use much power.



I would bury that cord in the dirt in the planter and then have this lid on it. It should gradually heat up the soil and the whole planter. I may even be able to start some plants early in that soil.



I could make the lid sloped for water run off. What do you all think of this idea?

[Hemlock140]

That could work as long as you don't start too early, because despite the warm soil the seedlings will suffer if it gets below freezing after they sprout. The problem I see is that your cover is too close to the soil, once the plants are an inch or two tall they will hit the plastic. I started my seeds last weekend, but they are in the house, on a table next to a window facing south.

[poncho62]

Yes, I agree it is too close. I will be setting it higher on another 2x4 ring and on a slope, higher at the back.

[guidoLaMoto]

It should work, but I see a couple potential problems--- As Hemlock suggests, you don't have much growing space between the soil and the top...Also, you may do better if you remove the soil and just put small pots in there-- less potential for root damage when you transplant (assuming you want to transplant).

In Ontario, your last frost date is probably well into May or June-- a heating coil in/under the soil may not adequately heat the air in there to protect the young plants.

Seed germination depends on soil temp, not air temp, so your seeds shouold sprout. It's what happens afterwards that may be the problem. https://extension.oregonstate.edu/ga...ed-germination

It looks like small planter-- No room inside for it for a couple months? Then you don't need the top, and maybe not the heating coil.

[Cambium]

Wonder if you can run an extension cord and plug in a regular Incandescent 100 watt bulb and put inside there. That would create some nice heat.


You can get one of these that plug into the extension cord and screw in a bulb


Get a thermometer in there too.


The other issue I see is airflow in there.. Without airflow seedlings may not be as healthy.

[Zoisite]

It should work for starting seedlings and for hardening them off quickly. Just make sure that if it's exposed to direct sunlight as well as electric heat in the soil then even on cold days it could suddenly get hot and steamy in there so you have to watch for heavy condensation and damp off (fungal rot). You may have to lift the lid a little bit sometimes to allow for air circulation and the release of excess humidity and heat. You'll definitely need a thermometer inside there.

I'd put up some boards around it or wrap a sheet of plastic around the bottom where the legs are so there isn't any cold wind blowing between the legs and under the box. It would be better insulated that way.

If it was directly on the ground instead of up on legs it would be what's called a box cold frame. Have you looked at pictures of different kinds of cold frames to get some additional ideas?

cold frames: https://www.google.ca/search?q=box+c...h=560&biw=1120

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[poncho62]

Looks like I am out of luck with the heat. The darn heat cable won't work above freezing it seems. Guess its just a cold frame for now. I do have a raised bed I can put the cover on so may try that. Thanks to all for the advice.