# Solar dirt sterilization over



## CesumPec (May 20, 2011)

I want to sterilize dirt/finished compost to make potting soil for use in my greenhouse. I've looked at solar over designs but I need to be able to make 100 lb batches or larger.

Can anyone suggest a link or design that might be appropriate? I'm tired of search google without success.


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## Belfrybat (Feb 21, 2003)

You want to be sure not to get the temps too high or you will kill the beneficial bacteria. What I do is make about a 6" deep "pile", water it and cover it with clear plastic. Any viable seeds will sprout and you can root them out. I do this with finished compost and with my raised planting beds early spring. Sure does cut down on weeds later in the season.


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## CesumPec (May 20, 2011)

I think I do want to get it hot enough to kill the bacteria. I can make a compost tea to add back the beneficial bact. Nematodes are a major problem in my area and can significantly impair high value crops like tomatoes and peppers. If I can kill the nematodes by cooking them to death, my seedlings will get off to a much better start.


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## TnAndy (Sep 15, 2005)

100lbs at a time is going to require quite a big 'oven', I think. 

If I were gonna make one, ( and I might get around to that project one day ), I'd simply build a wood box the slightly bigger than the glass panel used in standard sliding glass doors....those panels are usually tempered glass ( unless it's a really old door ), and 34" x 76" in size, IIRC, .....so the box would end up about 36 to 38" wide and about 80". Box depth would be about 6" or so. You could insulate it with foam board, but I suspect that would be over kill.

Then I'd put about a 2" layer of dirt you want to sterilize in...not get TOO deep so the heat would penetrate well, and set the box out in direct sun. If you could drill a hole and run a temperature probe in the box at the bottom of dirt level, it would let you know when that bottom layer hit couple hundred degrees. Couple days in the sun, empty, and refill.


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## TnAndy (Sep 15, 2005)

double post for some reason


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## CesumPec (May 20, 2011)

a used patio door is a good idea, ghanks Also need to come up with a way to easily unload, maybe tip the box up and everything slides out one end.


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## Buzz Killington (Jan 12, 2012)

Not trying to put words in TNAndy's mouth, but I think what he was suggesting was something on the order of a big cold frame that could be put directly over your pile o' dirt so that it could just be lifted off. That way you wouldn't have to "unload" anything, it's all just right there.

If you're determined to close it off, a possible way might be to just lay down a black tarp, put your dirt in, cover with your "oven" and then staple the plastic to the outside of the oven. When it's cooked, just unstaple and remove, and all your soil is right there ready to be moved by sliding the tarp to wheree'er it's needed.


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## CesumPec (May 20, 2011)

see, that was why I asked. I tend to over engineer things and you just made it WAYYYYY easier. Thanks Buzz


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## Jim-mi (May 15, 2002)

But . . . . . . . with the cold frame idea you will never know how deep the 'toad killing' temps have gone . .and it will take longer . . . . . .

Where as with Andy's idea . .with insulation also on the bottom heat will be retained longer and a cooking probe temp will tell you when the "batch" has reached such and such temps.

careful on the 'dumping out the end' idea . . . . . .those door walls are heavy ............


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## CesumPec (May 20, 2011)

I'm thinking combine both ideas. Bottom layer insulation, Next layer, some poly tubing running from an extra solar hot water heater which will sit beside the dirt oven, then plywood covered with a tarp upon which the dirt will sit to keep moisture out of the plywood bottom and ease dirt removal. All that is open sided. 

To cover all that, build a cold frame type bottomless box, plywood insulated sides and a glass top. Suns cooks directly from above, solar hot water heats from below. 

Get a probe thermometer to measure deep in the pile of dirt, which ideally will be read through the glass top. 

To empty just lift off the top box and shovel away until it is light enough to lift the tarp.

Hmmm...if I built this in a raised platform, I might be able to tip the finished batch into the loader bucket, or push it off into a wheelbarrow. 

OK, what am I forgetting? 



I might be able to get well more than 100 lbs of dirt cooked in each batch.


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## solidwoods (Dec 23, 2005)

If someone has already suggested this sorry not much time to read right now.
How about set up a wood burning stove outside with a metal box on top, thermometer, heat and stir maybe 10-20gl at a time for a crude set up.
If you will do this often set it up for bigger production.
Maybe put the stove in the greenhouse as back up heat also.
jim


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## CesumPec (May 20, 2011)

since I live in Florida, the need for a wood stove is rare. much cheaper, easier to have a solar powered oven


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## blufford (Nov 23, 2004)

CesumPec said:


> I want to sterilize dirt/finished compost to make potting soil for use in my greenhouse. I've looked at solar over designs but I need to be able to make 100 lb batches or larger.
> 
> Can anyone suggest a link or design that might be appropriate? I'm tired of search google without success.


 
As my horticulture instructor used to say. "Dirt is something you sweep up off the floor, soil is what you grow plants in."


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## wy_white_wolf (Oct 14, 2004)

Because of the larger batch size I would suggest looking at designs for solar kilns instead of ovens.


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## CesumPec (May 20, 2011)

Good idea wolf


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## SolarGary (Sep 8, 2005)

wy_white_wolf said:


> Because of the larger batch size I would suggest looking at designs for solar kilns instead of ovens.


Don't know if these would get hot enough or not?
http://www.builditsolar.com/Projects/WoodDrying/wood_kiln.htm

Gary


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## kbabin (Aug 1, 2006)

what about using something like this?

http://www.northerntool.com/shop/tools/product_200336228_200336228


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## greg273 (Aug 5, 2003)

I dont know about the poly tubing, seems like an added complexity...

I do like the patio-door, 'raised bed' type idea...

We sift our compost onto a sheet of leftover galvanized metal roofing, its easy to pick it up, fold it a little and put it into a bucket... A 5-gallon bucket of sifted compost is pretty easy to lift that way. 

Tarps dont hold up well to UV exposure and heat, so they might not be the best. With a sheet of metal roofing, like the corrugated stuff, you wouldn't need a tarp. 

You talking about something about 5 times larger though, but possibly you could make the cooker smaller, just run batches through more often. You guys get a lot of sun and warm temps down there, so it should have a quick turn around time... 2-3 days maybe? Less? Much faster in summer... Then you could stockpile it for the fall.


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## greg273 (Aug 5, 2003)

kbabin said:


> what about using something like this?
> 
> http://www.northerntool.com/shop/tools/product_200336228_200336228


 Ha! Thats pretty cool for this application... Just roll out the finished compost! Not sure how that material would take the heat though. Sure would be a good way to unload the finished product!


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## CesumPec (May 20, 2011)

kbabin said:


> what about using something like this?
> 
> http://www.northerntool.com/shop/tools/product_200336228_200336228


I've got a homemade version of that that I use all the time. It's a 2x4 attached to a piece of plywood the width of the flatbed pickup and attached to that is a chain which extends from the front of the bed to hanging off the rear. My chipper shoots directly into the truck. When I want to dump the load, I attach the chain to a 10K lb loading strap that is wrapped around a tree. I drive away and the load comes out in a nice neat pile. 

l


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