Using Free Soil To Start Seeds: How to sanitize soil

using free soil to start seeds
 -You don’t need to buy special starting mixes to start your seeds. Here I’ll teach you how to use free soil to start seeds. –

Just before we got married, my husband and I were starting our first garden in western Washington.  AJ was working in a greenhouse at his college and he had all he could want in the way of spent soil and compost. He wanted to save money and use it for starting our seeds instead of buying commercial starting mixes. I was leery of plant diseases since the compost pile hadn’t been maintained at a temperature to kill them. He assured me any diseased plants didn’t go into the pile. I was still resistant to the idea but he nagged and whined and poked until I finally decided he could have his way.

When he brought the soil home I noticed right away that there was a very healthy population of millipedes or centipedes, I don’t remember the difference now, the itty bitty ones were what we had. I did some internet research and couldn’t find anything about them eating seeds or seedlings so I grudgingly used the soil.

Then I waited.
And waited.
Until I knew something was wrong because something should have sprouted by then.
using free soil to start seeds


Well my friends, those little demons do eat seeds. Most veraciously, and I’m very sure they would have happily munched on seedlings too. They would chew through a weak spot in the seed coat, usually were the radical (seed root) would emerge from and eat the seed from the inside out. 

I don’t think they are anything to worry about out in the garden, and beneficial in the compost pile, but in a seeding tray where all they have to eat are your precious seed and seedlings, they are very much a problem. So I had to start everything over. It was painful, we were already late getting them started and now were even further behind and neither of us really had money to buy a starting mix since all my money was being funneled into the wedding and we were both poor college kids (um, we still are actually).
using free soil to start seeds


So, I got creative. I figured compost piles get pretty hot and heating the soil would kill the bugs. I decided to try it since the worst case scenario I could think of was totally killing all the soil bacteria.

The good news, It worked!
We didn’t have anymore millipede problems and our plants grew just fine.
This year I find myself with a place to have a garden that was totally unexpected, and broke. So very broke, that I’m once again making my own starting mix.

How to Sanitize Soil – or Using free soil to start seeds

~One 5 gallon bucket is enough to fill 2-3 standard 21 x 11.5 inch planting trays of 3.5 inch pots.
~300F for 15 minutes, add more time if soil is very wet or using deep dishes.

 Picking your starting soil

using free soil to start seed
The best thing you can use is finished compost, otherwise a sandy soil will work fine, you will just need to feed your starts more or add compost to the soil. By “finished compost” I mean decomposed manure, bedding, plant matter that smells like soil and has a nice deep color and rich smell. If it’s not finished it will be chunky and smelly.
 Starting with a soil that contains a lot of clay would probably turn into a disaster. Clay is the worst to try to start seeds in and heating it is liable to make weird pseudo-pottery. If you have a very dense soil and a little money buy some perlite or vermiculite to add to it; it will make the soil fluffier and a little bit goes a long way.

Try to gather your soil on a dry day. I know how impossible that can be, just know if its sopping wet you might have to  break up a lot of clumps or even lengthen the heating time to get the soil warm through.

Pick out large rocks, sticks and any worms or carabids (big black, sometimes iridescent, super beneficial beetles) and return them to the great outdoors to bless your garden later.
Preheat your oven to 300F. A lower temperature would probably work, but the numbers below 300 are rubbed off my toaster oven and at 300 I’ve still had a few critters come out alive. 

using free soil to start seeds
Fill whatever baking pans you’ve decided to use and pop them into the preheated oven. 15 minutes does the trick. I set a timer and have multiple pans going so I can get it done quickly. 
Poor your heated soil into a clean food grade bucket (we don’t want any BPA in our soil, now do we?)  or box without lots of holes. You can let it cool all the way before you use it or just enough that it’s not steaming anymore and you can comfortably run your hand through it. 
using free soil to start seeds
using free soil to start seeds

If you are trying to kill a specific disease you should look for information about what temperatures kill it and adjust the process if needed. 

 Break up clumps as you fill pots, toss any larger bits into the bottom of pots so you have an even soil surface.
 That’s all there is to it folks, plant those seeds to your hearts content!
using free soil to start seeds

This post is participating in the HomeAcre, Savoring Saturdays and From The Farm blog hops, check them out to find other great blogs like ours! 

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10 thoughts on “Using Free Soil To Start Seeds: How to sanitize soil

  1. Any idea if heating the soil that hot kills any of the beneficial micro-organisms in it? Thanks for sharing this at Savoring Saturdays. 🙂

    1. Oh yes, it kills at least some of the little guys, such is the price we pay! But, if you fertilize with compost tea when the sprouts emerge I think it probably won’t negatively impact the plants in the long wrong. Thanks for stopping by!

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