Bake Soil to Pasteurize Before Germinating Seeds

Make (Prepare) Your Own Soil To Germinate Seeds

A ‘do it yourself’ soil treatment for germinating seeds.

If you buy ‘special’ soil at the store for germinating seeds, it has most likely been through a pasteurizing process (not to be confused with sterilized).

You might wonder why it may help to germinate seeds in soil that has been through a pasteurization process… It’s because the process eliminates some of the organisms and spores that could harm your seedlings. The process will eliminate most diseases, weeds, insects, weed seeds, and fungi in the soil.

It is also safe practice to pasteurize regular potting soil bought from the store prior to planting seeds, although they do make special purpose potting mixes for germination.

The do-it-yourself procedure is pretty simple. Here’s how:

How To Pasteurize Soil For Seed Germination

Add soil to a baking pan
Cover the pan with aluminum foil
Bake at temperature between 140 and 180 degrees Fahrenheit
When internal soil temp reaches 140, continue at temp. for 30 minutes

Do Not Heat Above 180 Degrees F

For best results, do not let the temperature rise above 180 degrees Fahrenheit. Here’s why…

When soil is treated at 140 degrees Fahrenheit, most of the beneficial microorganisms survive. Their presence stops or slows the growth of plant diseases.

When soil is heated above 180 degrees Fahrenheit, this may cause a buildup of harmful substances in the soil and will kill all microorganisms (including the beneficial ones). This may cause diseases to spread very rapidly (with the absence of the beneficial natural enemies).

(Reference: saddleback.edu Propagation Soil Preparation)

Tips

Preferably use moist soil (not dry, not soaking wet). If dry, add some water and mix it up. If wet, then let some evaporate out first. When the soil is squeezed in your palm, it should clump together somewhat.

Ideally, use a ‘meat thermometer’ due to its ideal temperature scale range. Poke a hole in the foil and insert thermometer until it is about in the middle of the soil depth. Be sure to use a thermometer that is oven safe if you’re going to leave it in there.
CDN Meat/Poultry Ovenproof Thermometer

You can also use a non-oven-safe thermometer by sliding out the oven tray and occasionally checking the internal temperature for 140 degrees.
Taylor Precision Instant Read Pocket Thermometer

Note: Be prepared for an unpleasant odor (My experience actually has not been too terribly bad)… Your experience will vary – depending on your soil. Definitely turn on the vent hood external fan if you have one!

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23 Comments

  1. Just yesterday, I was just reading about a process called soil solarization. I had checked out a couple of gardening books at our local library. This one is “The Harrowsmith Country Lifebook of Garden Secrets,” by Dorothy Hinshaw Patent & Diane E Bilderback, published in 1991.

    Their method has to happen the previous year during the hottest part of the summer. You moisten the soil and cover it with a clear sheet of plastic. Then leave the plastic on for one to two months. This method supposedly kills the harmful organisms but leaves the benign ones, and you don’t smell up your house.

    Although a quarter of a century old, I found this book VERY helpful. I plan to check it out again closer to planting time.

    1. Sorry, that should be Country Life Book, not lifebook. I see it is available on Amazon. Unlike other gardening books I have read, it doesn’t just explain how to do things, but WHY. You get a botany lesson.

  2. Good article Ken
    I do something a little differently though, when I’m starting seedlings I prep my trays with good garden soil, I sift the soil through a 3/8″ screen, and fill the trays. Set them outside in the hot sun and cover them with black 6mil plastic for a week, this has the same effect I’m guessing. I literally solar bake the soil outside. Has seemed to work well. Thinking I will do a test on the temp this year, just to compare notes.
    NRP

  3. now upfront, I will tell you we did not use a meat thermometer to check the temp…so, no real idea what temp we got to…

    but..

    years ago my husband had the idea he should Pasteurize the soil we used indoors. I was not at all happy with the “result”
    – stunk terribly
    – after a number of bakes (cant recall how many) I realized it appeared to be coated the interior of the oven somehow. It would not clean off, even on self clean. No idea what the heck happened.

    After this, he then baked it in the outdoor bar b que. (still stunk terribly)

  4. I have used the black plastic tarp too to bake the soil in my garden for two weeks. It also kills weed sprouts when watered and then covered, so there aren’t weeds growing along with your veggie sprouts in the old soil.

  5. Do NOT bake soil in the house in the oven. Your house will smell terribly!

    Go with a solar-heat approach: use tarp, plastics, etc.

    If you have a soil-testing kit, you can actually make your own ‘potting soil’ with your local soil from the back yard/garden/compost/woods’ soil. I add in some sand, composted manure, coconut coir, vermiculite (for micronutrients and aeration) then test…then add in the necessary micronutrients via products like greensand, bone meal, blood meal, etc..

    You will REALLY learn your soil by doing it yourself. Also, it is so much less expensive than buying those expensive “potting medium” bags. Plus companies that produce products like Miracle Grow are owned by pro-GMO Monsanto corporations like Scotts (they produce Miracle Grow, along w/ GMO products).

  6. We have been using plain old peat moss in the nursery for years seems to work fine.We start most of our plants for retail in jumbo six pacs then shift them up to 4″ pots when they have enough roots. The peat seems to dry at an even rate so we can water all of our starts at the same time. Second choice would be a bag of Miracle grow potting mix, the most expensive type they offer, A bag will last 2 years or more depending on how many trays you plant. Their mix is basically peatmoss and some wetting agent as well as starter fertilizers.

    1. I do my initial planting in sphegnum moss. Keeps the seeds evenly moist and even if there’s too much water in the tray underneath they don’t get waterlogged. When I transplant I put the seedling with the moss straight into the soil.

  7. Ohhh, I learned something new today…:) Keeps reminding me why I like this site best. Two thumbs up for Mr. J and everyone on here.

  8. We have tried making our own seeding soil several times in the past but with marginal success. We stopped several years ago as the plants just don’t seem to grow well in our home made stuff and figured we are getting too old and impatient to continue experimenting and it’s easier to buy commercial stuff and be done with it.

    Have had much better results using commercial seeding soil or just planting things directly into the ground as opposed to using our own homemade seeding soil. Haven’t cooked any in the oven yet and don’t plan to. We stock up several hundred pounds of commercial seeding soil (not potting) and use it for starting seeds only. Probably have enough to last a couple years but we generally use the 1st in 1st out rule and keep updating our supply each year. I think we have 8 or 10 bags in the greenhouse. That might be a good prep item to stock up on.

    Some things require getting the jump on either cold or heat so we have to start tomatoes in the greenhouse early (in January) when it’s too cold to plant them outside. That way we can set them out early and beat the bugs and summer heat since tomatoes don’t like the hot weather we have down here. On the flip side of the season we have to start cabbage in a shaded part of the greenhouse in August when it’s too hot and Collards in September otherwise the plants will bolt. We set them out in mid to late September and they generally do nicely. Start harvesting Napa cabbage in November and regular cabbage in December through February. Same thing with lettuce on both ends of the season. Everything else gets sown directly into the ground.

    I suppose when SHTF and we are thrown into TEOTWAWKI then we will have to bite the bullet and just plant everything directly into the ground, after we run out of the commercial stuff.

  9. Simply cover the soil to keep it moist and keep it in the dark so the weed seeds will germinate.
    Like our bodies, the “Good” organisms and the “Bad” organisms are in balance. When someone takes an antibiotic for a Streptococcus infection, all of the family is wiped out, not just the one making us feel ill. The Streptococcus that live with us and do us no harm are in competition with the one that does and protect us from the nasty infection. Ever notice the reoccurring cycle of infection?
    So don’t wipe out a biosystem, just get rid of the weed seeds.

  10. Sometimes it helps to learn new science.
    Think of making compost. Do you heat that to sterilize it? Fungi, bacteria, and all sorts of critters live together and are beneficial to our plants. Why destroy it?

    1. @ OMG!!!!

      Sometime it helps to learn how read.

      What is so very difficult about this sentence, one of the first in the article?

      “If you buy ‘special’ soil at the store for germinating seeds, it has most likely been through a pasteurizing process (not to be confused with sterilized). “NOT TO BE CONFUSED WITH STERILIZATION”

      How about this sentence

      “When soil is treated at 140 degrees Fahrenheit, most of the beneficial microorganisms survive.”

      Or the remaining article about NOT heating the soil to sterilization?

      Good luck with the comprehension skills, Read the words, not what you think they are.

      NRP

      1. I long since accepted the fact that reading comprehension is a lost art. If it doesn’t come in sound bytes or a meme, it’s lost.

      2. It is a shame when people are not open to new ideas. Gardening in a way that is compatible with the natural cycle is now very well accepted. Some of us know how to treat the soil as the living thing that it is. Nature has a balance. If you can learn how to work in a compatible way, you may find a greater gardening success. There are a great many sources for the information that may be of interest to those that wish to continue their education. I do realize that it becomes harder for older people to learn and that they stay with old ideas as part of the aging process, but an effort may help slow the process.

        1. @ OMG!!!
          Ya know ya young-fool, you were actually having a conversation until you have to act your age.

          “I do realize that it becomes harder for older people to learn and that they stay with old ideas as part of the aging process, but an effort may help slow the process.”

          So, again for the umpteenth time, read the article, read the comments. You may find that a few classes at your local Junior High School may help your comprehension of the English Language.

          As far as your “new” science, how’s those millions of tons of Monsanto chemical fertilizers and pesticides that are poisoning the farm-lands working out for you? And all of the GOM’s that have less and less nutritional value? How about your “new science” that’s working out for you in the food tasting like plastic that your promoting as you talk “new science”.

          Do not make the foolish conclusion the “older people” don’t already know what your spouting.

          I would suggest you not take it for granted us “older people” don’t know how to grow a garden and tend the soil. You might even learn something from one of those “older people” if you could find one that would put up with your sarcasm in believing your the only one around that knows Gardening.

          Have a nice day, I’m done with the sorts of you, your mindset is not worth the time.

          NRP

    2. In a well structured compost bin or pile the temps can easily get up around 200 degrees. Mine usually hover between 140 and 160 when “cooking.” The critters seem to survive just fine.

    3. @OMG!
      Actually, it is fungal disease that is the worst culprit for seedlings: damping off. That disease includes a variety of root rot diseases along with some fungal molds.

      If you use compost in your potting medium, you must be prepared to kill off some of the non-beneficial microbes. The best action(s) to ward off any of those damping off diseases is to use daily sprays made w/ chamomile or nettle tea, or to do a one-time dusting of ground cinnamon on the soil surface. These natural methods with beneficial herbs & spices do work. I raise some orchids and ground cinnamon is commonly used on the root trims of orchids.

  11. I once boiled the soil I was going to use in a raised bed back in Virginia in an attempt to thwart squash vine borers. They got in any way. Not a problem where I live now but I still have problems with squash. My favorite vegetable too.

  12. I just baked some soil now. This my first time trying this.I will mix it with commercial garden soil. I have never had problems growing plants in ordinary untreated yard dirt. However, I am going to grow in the house this time. I don’t want to bring the bugs inside.

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