2 Potting Soil Dilemmas

Hi all,
We're growing microgreens and we have a field where we are growing saplings and some annuals. Here's the product page:
http://www.brill-substrate.com/pdf_files/eng_produkt-db_profi/brill_bio_start_eng_08_2014.pdf

I'm running into 2 big dilemmas with potting soil. So I know that using peat is not good. We grow in nursery flats with it and in 10 days it can't be used again. We've tried recycling it but the result is not so good, and storing it indoor brings the insects we're trying to keep away from the microgreens.

Dilemma 1.
The alternative is coconut-coir which we evaluated using, but decided against it for the high cost and the anti-fungal agents and fertilizer that might be necessary. Is there anything that prices near potting soil (we're paying 6.50 euro/70 liters) that doesn't require more chems?
It's important that the substance we use is rather pure of microorganisms and soil fauna, since we're doing this indoor. Don't really want to go hydroponic.

Dilemma 2.
If we continue to use potting soil, what are some further uses we can put it through so that it really stays high in the order of uses? I thought of mushrooms, but it seems potting soil can't be sterilized easily and my first experiment has flopped. We have zero experience in that area. Putting it to service as potting soil for trees is a good idea, but I have a limited number of pots, plants, and water to do that. The nutrition in the potting soil is still high, it even has seeds that will germinate. I could sell it to defray the costs, but i don't think anyone would be interested.

I could just put it all into vermicomposting, but I feel that would be a waste of a still high-grade product. It would also require about three, 1 meter cube flow through worm bins that I really am too busy to construct.

The quantities are so large (and growing) that whatever solution has to scale easily. Microwaving 200 liters of soil for mushrooms is not going to happen.
I've been wracking my brain about this one for a couple weeks and though some help might be in order.
thanks,
William

ps: I'm hoping to find a solution before the whole lot of it ends up in a big pile somewhere doing nothing, which would be a total disaster.

well i do a lot of sheet mulching, so used potting soil ends up in there often. although i usually use it a few times, by adding it to larger piles of freshy bag soil/sand and reusing it in new pots.

adding sand to your potting soil thins it out and make it work better. for starter plants they dont need much for nutrients, so a heavy sand ratio in the mix makes the bag soil go a lot futher. sand is a surprisingly good growing medium, so i am more and more realizing.... only it doesnt have nutrients at all...but even by itself can start seedlings. some things like it better than others though.

then like i was saying i do sheet mulching, so adding it to the wood chips/straw/manure/local soil big mixed up layers...works well for me. it ends up disappearing into the layers....

as for sterilizing soil in big batches, if you can have a fire pit open bonfire type fire, at the safe times obviously, then you can cook the soil on that. either in a big pot type thingy, or just straight on the fire. keep throwing on more actual kindling type stuff, and then thin layers of dirt as the fire burns. it may not get to the perfect sterilization temperature, evenly, but it will somewhat sterilize the soil. if you have some kind of nice set up fire pit with a large...pot or metal piece to hold it above the fire, you can get it really hot. its quite a project though.

Sand is a good idea to stretch the current mix.

You could use the used soil to start larger plants, something like culinary herbs. You should have a good market for windowsill herb gardens within your existing customers. Or find a nursery already doing that and make a deal on the soil.

Just so I understand, Would you like to reuse the potting mix if you could?

I thought I'd look at how to sterilise potting mix on a large scale and I found the cheapest way and the simplest without using an oven or microwave to sheet steam it. I found this information and I hope it helps. I am sure it can be adapted.. Using solar etc. does this help?


Large area sheet steaming in greenhouses using a steam injector.

Surface steaming with special sheets (sheet steaming) is a method which has been established for decades in order to steam large areas reaching from 15 to 400 m² in one step. If properly applied, sheet steaming is simple and highly economic. The usage of heat resistant, non-decomposing insulation fleece saves up to 50% energy, reduces the steaming time significantly and improves penetration. Single working step areas up to 400 m² can be steamed in 4–5 hours down to 25–30 cm depth / 90°C. The usage of heat resistant and non-decomposing synthetic insulation fleece, 5 mm thick, 500 gr / m², can reduce steaming time by about 30%. Through a steam injector or a perforated pipe, steam is injected underneath the sheet after it has been laid out and weighted with sand sacks.

The area performance in one working step depends on the capacity of the steam generator (e.g. steam boiler):

Steam capacity kg/h: 100 250 300 400 550 800 1000 1350 2000
Area m²:
15-20
30-50
50-65
60-90
80-120
130-180
180-220
220-270
300-400
The steaming time depends on soil structure as well as outside temperature and amounts to 1-1.5 hours per 10 cm steaming depth. Hereby the soil reaches a temperature of about 85°C. Milling for soil loosening is not recommended since soil structure may become too fine which reduces its penetrability for steam. The usage of spading machines is ideal for soil loosening. The best results can be achieved if the soil is cloddy at greater depth and granulated at lesser depth.

In practice, working with at least two sheets simultaneously has proven to be highly effective. While one sheet is used for steaming the other one is prepared for steam injection, therefore unnecessary steaming recesses are avoided.


I also found this research paper for plastic sheeting techniques using the sun. http://www.fao.org/docrep/006/y5031e/y5031e0g.htm

Thanks for the replies.
First of all, I do want to re-use as much as possible the potting soil - in various ways.

Putting it into seedling or tree production is slightly a problem because I have a limited water supply. I could do it from October to May, but not much grows then.

Increasing my supply, as mentioned via sand, is also a problem because I have too much already.

I could sell it off, but I don't have any interested buyers and the fact that it's used is probably going to hurt that idea. Oh, and the fact that it has seeds in it. And there would be no more uses to gain from it, although it would mitigate my cost of potting soil.

Vaporizing it is potentially an idea, but the process doesn't look like it scales down enough to make it do-able by me. Plus I don't know if that would be enough for mushroom production, which is probably the only reason I would make an effort to vaporize.

Thanks again for now.
William

Then I would more seriously look at hydroponic production in sand or perlite that can be easily solar or fire pasteurized.

You can do bunker spawn of king stropharia or other soil grown varieties. Probably need to add manure and straw or wood chips. It doesn't need to be sterilized, but you do run the risk of getting something different than you planted. Put it in coffee bags or big windrows and let it go. You need moisture, so it will probably be seasonal for you.

Can you not sterilize the soil by solarizing it in heavy black plastic bags?

Hi Tyler,
I don't think sterilizing soil on principle is really worth it, but that's just the way I've done things so far (feeling that nothing is really broken, so why fix it).

I have no problem re-using it as potting soil and maybe adding a little compost (even though it really doesn't need it, since these bags were used to grow microgreens).

The main problem, once again, is the fact that I cannot use it enough for the amount that keeps coming in.
I have a usage problem, and consequently, a waste problem.

My proposed usage right now is to make grow bags and grow flowers off them. It seems to me the best and quickest way to get another product off of the soil before putting it to a third use.

https://permies.com/t/50648/gardening-beginners/Thoughts-DIY-Grow-Bags