Sterilized Soil a Bad Idea?

SteveHillageMay 27, 2014

Hi. New to garden forum. New to gardening.
I have so many questions.

I buy pre mixed soil. It's called Island's Finest All Pupose Potting Mix.

I believe it is sterilized and I heard some where soil sterilization can be bad if you use compost because it kills the essential bacterias needed to break down the compost.
Is this true? Organic fertilizer is a must for me, should I continue using sterilized soil?


Thank you for reporting this comment. Undo

Starting seeds in sterilized soil is fine, but after the sterile soil joins compost it will add goodies to your sterile soil, but won't hurt the compost.

    Bookmark   May 27, 2014 at 10:00PM
Thank you for reporting this comment. Undo
johns.coastal.patio(USDA 10b, Sunset 24)

All potting soil gains microorganisms over time. They blow in. If you'd like, you can hasten this by going outside, getting one pinch of good soil, and dropping that one pinch in your pot-plant. Most people are not aware that there are literally millions of "critters" in each gram of soil, which equates to about a good pinch of soil. These "critters" are bacteria, actinomycetes, fungi, yeasts, protozoa, algae, and nematodes. They are microscopic organisms that live in the soil. It sounds terrible, but we exist today because of them. They are what give the soil life, which is necessary to grow plants, the backbone of our existence.

- Steve Jones, Master Rosarian

    Bookmark   May 27, 2014 at 10:40PM
Thank you for reporting this comment. Undo

Is this potting soil or "garden soil" you are referring to?
Potting soil is not soil but is a growing medium made of peat moss, coir, or finely ground bark, or a combination of those and the Soil Food Web will not be present in that for quite some time. That is one of the reasons many organic growers do not consider container growing to be organic.
Sterilizing garden soil could kill off most of the Soil Food Web which would mean time would be necessary for them to recover, a long time, like years, although putting good, unsterilized compost into that soil might help.

    Bookmark   May 28, 2014 at 6:29AM
Thank you for reporting this comment. Undo
toxcrusadr(Zone 6a - MO)

There will be more microbes in fresh compost than in soil, and if you mixed compost into sterile organic matter the microbes will grow and spread. I don't think potting mix would actually be sterile, it looks like the finer bits are already composting so there must be microbes in there.

If you're just transplanting flowers or veggies into pots or containers, you certainly don't need sterile medium. Actually, microbes do a lot of the work of managing nutrients and feeding plants.

    Bookmark   May 28, 2014 at 11:48AM
Thank you for reporting this comment. Undo
johns.coastal.patio(USDA 10b, Sunset 24)

kimmsr, I posted a study a little while back ... ah, here we go: Seedlings were germinated in seven different sand- or soil-based and artificially based growth media. Seedlings grown in the HFC had fewer mycorrhizal short roots than those grown in the open greenhouse atmosphere. Furthermore, the proportion of seedlings from the HFC that were completely non-mycorrhizal was higher than that of seedlings from the greenhouse atmosphere. Seedlings grown in sterilized, artificially based growth media (>50% peat moss, vermiculite, and/or perlite by volume) had fewer mycorrhizal short roots than those grown in sand- or soil-based media.

Leads me to believe it happens fast. (The study is actually about reducing the effect, in order to maintain truly sterile conditions. They have to use "a high-efficiency particulate air-filtered chamber" ti achieve that.)

(The hat tip at the end to "sand- or soil-based media" is a bonus of course.)

Here is a link that might be useful: airborne ectomycorrhizal fungi

    Bookmark   May 28, 2014 at 1:39PM
Thank you for reporting this comment. Undo
toxcrusadr(Zone 6a - MO)

Soil is terribly hard to truly sterilize, BTW. I used to work in a lab doing biodegradation studies on pesticides in soil. We were supposed to have 'sterile control' samples to gauge any non-biologically mediated degradation. We'd sterilize the soil in an autoclave, and the samples were incubated in sealed sterile jars, but after a few weeks there were always bacteria in the sterile ones. Fewer of them, but still a lot - maybe 10,000 per gram compared to 10 million in the unsterilized soil. I think you'd have to autoclave it several times, days apart to really kill it.

    Bookmark   May 28, 2014 at 2:57PM
Thank you for reporting this comment. Undo

I've spent a lot of time reading posts on Garden Web and some of the people posting here are pretty informative. Unfortunately, and it's not limited to this forum or these posters, but most of the time people don't answer people's questions.

Your answer: No, sterilized soil will not kill off bacteria added to it.

    Bookmark   May 29, 2014 at 12:37AM
Thank you for reporting this comment. Undo

"should I continue using sterilized soil? "
It is not necessary.

    Bookmark   May 29, 2014 at 7:18AM
Thank you for reporting this comment. Undo
johns.coastal.patio(USDA 10b, Sunset 24)

It is actually unclear if the OP is mixing anything, or referring to the organics in their original mix as "compost."

    Bookmark   May 29, 2014 at 10:56AM
Thank you for reporting this comment. Undo
toxcrusadr(Zone 6a - MO)

Upon rereading the OP's question I think the issue is actually whether the lack of microbes in sterilized soil (or potting mix, etc., doesn't matter) will result in an inability of that matrix to continue breaking down organic matter (compost) added to it. I would say no, because compost has loads of microbes of its own. I hoped that my statements about potting medium containing compost and it being nearly impossible to really sterilize these materials anyway, would have made that clear but perhaps not.

    Bookmark   May 29, 2014 at 11:59AM
Thank you for reporting this comment. Undo

Hi all, I have a closely related question-- I'd like to experiment with more 'alive' soils for indoor plants and I have lots of materials outdoors to work with.. My concern /question is, can I sterilise the media enough to remove insects without seriously depleting the microbial biota? I don't need to do massive quantities at once, so even more labour intensive /fussy approaches could be possibly used-- eg- could I use water to kill insects/worms etc, or would that be just as damaging to the microbes?

    Bookmark   October 5, 2014 at 4:26PM
Thank you for reporting this comment. Undo

Sorry, no. Sterile means sterile - the process of sterilization is intended to kill off any living organisms, pathogenic and benign.

And I'd have to question the advisability of working with "alive soils" in any container growing situation. 'Alive' would connote the inclusion of your typical soil microorganisms and they need organic matter to survive. Including organic matter - like compost - in any sort of significant percentage as an ingredient in container/potting soil is not recommended. Most commercial potting soils contain little to no organic matter and are comprised almost entirely of relatively inert ingredients.

The reason for this is that organic matter will continue to decay and breakdown over time into smaller and smaller particles. As this happens, your soil loses its porosity and ability to drain freely and plants suffer due to lack of adequate aeration and retained water. Potting soils with a high component of OM eventually (and more rapidly than you would expect) become a mucky, gooey, water-soaked mess.

    Bookmark   October 5, 2014 at 7:47PM
Thank you for reporting this comment. Undo
toxcrusadr(Zone 6a - MO)

Not to sound nitpicky but if potting soil is ground bark, coir, peat moss etc. those are all organic matter. The only part that would not be is perlite and vermiculite that is sometimes used. The difference is that bark, etc. used in potting soil decomposes very slowly in the pot (compared to a compost pile with high nitrogen 'greens' added). I completely agree on that last line about muck and goo, but I think that happens when *composted* organic matter is used, i.e. compost.

    Bookmark   October 6, 2014 at 1:47PM
Thank you for reporting this comment. Undo

You are correct, tox. They are organic matter :-) But they are pretty inert organic matter - neither peat nor coir tend to decompose or breakdown any further to any significant degree and as you note, bark decomposes very slowly in a potting mix. Because of this, they offer minimal support to any microbes that may be present.

To encourage the 'live' component the poster was referring to requires undecomposed or only partially decomposed organic matter - compost, manures, leaf mold, whathaveyou. And that's where the problems originate. It's also why organic fertilizers, seldom water soluble, are not a great way of addressing nutrient needs in container growing.

It is tough to reconcile a "good" potting soil with an "alive" potting soil - the two are counterproductive.

    Bookmark   October 6, 2014 at 9:18PM
Thank you for reporting this comment. Undo
tropical_thought(San Francisco)

I would rather use sterilized soil if I was using that kind of thing, to prevent things like diseases and weed seeds being imported to the garden. All the soil food web will come from my compost already in place. It is silly to panic about the soil food web. Earthworms are not even native to north American by the way, look this up. They don't have to be there to create healthy soil. In fact earth worms have harmed some forests because the ate up all the organic layer and the soil then was damaged. I would rather not have earth worms, but I have tons of them, too many to ever get rid of them.

    Bookmark   October 6, 2014 at 9:55PM
Sign Up to comment
More Discussions
What to do with old container soil?
I live in a very small suburban yard and must use containers...
Need advice on watering succulents with new soil
I recently began using soil-less soil, as has been...
starting a new nursery/retail landscape supply business
lots of good reading here. I am looking at starting...
Animal Bedding Pellets for mulch?
I use white pine bedding pellets in my horse's stall....
Hapi-gro 100% Organic Compost
Can I plant straight into this?
Sponsored Products
Domino Blue Rectangular: 5'3 In. x 7'6 In. Rug
$159.00 | Bellacor
Breeze Outdoor Pillow - Breeze Poolside, 12" x 20"
Grandin Road
Garage Storage Systems & Accessories: Husky Garage Shelving Secure Lock 22-1/2
$5.97 | Home Depot
LenguaLink´┐Ż (Spanish) Rectangular: 5 Ft. 4 In. x 7 Ft. 8 In. Kid Essentials - La
$255.95 | Bellacor
Zephyr 36W in. Milano S Island Range Hood - ZML-M90BS
Midtown Burnished Bronze Circular 11" Wide Foyer Chandelier
Lamps Plus
54" Minka Aire Timeless French Beige Ceiling Fan
Lamps Plus
AndTradition | Trash Me Table Lamp
$125.00 | YLighting
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™