That would work for small amounts of soil and boiling water would kill both the good and bad bacteria. How effective that might be depends, too, on how long the heated water stays in contact with the soil.

Back in Late January, I did it for some old perlite I had around for years in a musty area of the basement. I made cuttings from my blueberry prunings and I wanted as sterile a medium (peat and perlite) as possible. Seems to have worked, but then again I didn't use a control group with un-'sterilized' perlite.

I boiled the water in an old pot and poured the perlite into it. I never tried it with soil, but if I needed, I think I would do the microwave method.

a sterile soil is not fertile. so why sterilize it?

And by the time the water had been carried into the garden and hit the soil it would be below boiling.

Why do you think you need to sterilize the soil?

rgreen, thanks, that's a reason to sterilize. I can see it for perlite (although never considered doing so). Perlite's, of course, a different substance from 'soil.'

A separate point: apart from the questionable benefits of sterilizing, one has to keep in mind that using boiling water on soil would not just affect the bacteria - it would have lots of different impacts on all of the other complex chemicals in soil. They wouldn't just be 'sterilized,' they'd be profoundly impacted and in ways that may not be beneficial.

Boiling water kills bacteria in the water you boil, not bacteria in the soil you pour it over. Because once you pour it over the soil, it isn't boiling anymore. I routinely sterilize the soil I use for planting seedlings and, as a result, never have troubles with damping off, fungus gnats, or fungal deposits in a medium I have to keep very moist. I don't need an active soil biome in that soil. I sterilize by baking it at 180F for an hour. No need to sterilize soil in general, though.

I don't even sterilize my seed starting mix...excellent results for years.

I can't imagine how pouring boiling water over soil would profoundly impact soil chemistry. Care to elaborate? I can imagine that with very high temps, >200C or so, you might see some changes. Especially as charring of carbon occurs and resulting breakdown of organic proteins. The physiochemical effect of really high temperature on soils has been looked at with some care with regard to forest fires.

I used to have all of those problems with my mix, until I started sterilizing. Maybe just my bad luck. I do use compost in my mix which, if kept moist and warm, leads to a biological free-for-all.

I doubt the average gardener would be able to get water reach a temperature of 200C. The boiling point of water in the centigrade scale is 100C, or 212F in the English (fahrenheit) scale.

I think the root of the question was how heating affects soil. But yes, throwing hot water on soil isn't likely to result in charring of carbon.

heating affects the soil biologically, and through biology, biochemistry is also affected.

The idea was to kill stuff. So much for biology. For planting seedlings, a biologically sterile mix is advantageous. The biochemistry that those organisms bring to the planting mix is not. When you plant out, that soil will be repopulated rapidly and add to the soil biome. Biochemistry will eventually thrive.

If you kill stuff, the soil chemistry won't be affected. Well, the NPK may increase, because those constituents in the soil organisms are destroyed.

We aren't talking about permanent sterilization.

If I wanted to flutter the dovecotes around here, that is exactly the kind of drive-by question I would ask! Or maybe I would ask "Should I buy Miracle Gro" or "I bought this topsoil..." or, you know, anything at all about compost.

Since nothing gets the posters here overwrought like a theoretical question that wasn't actually asked, perhaps littlemidgetmc could be more specific on what problem he or she is trying to solve. Does it have to do with the other question about "little white bugs"?

That's a fair point. I was assuming that the only reason one wanted to sterilize soil was for planting. But who knows? Maybe it was about wanting to take a clean mud bath.

The question was specific, however. It was whether pouring boiling water on soil would kill bacteria. The answer, if you read way up above, is probably not.

Boiling water, and steam, have been used to sterilize soil since the ancient Egyptians did that, but the water bath needs to stay in contact with the soil for a period of time (directions from different sources indicate 30 minutes to 5 hours) to be effective. It would not be as simple as pouring boiling water over some soil.

Yes, boiling water will kill bacteria provided it is done properly. That hot water is effective as a sanitizer is why you wash your food dishes in hot water.

Actually, I think that you use hot water to wash dishes because grease is more effectively removed with heat, and because the hot water penetrates better (the viscosity of hot water is lower than of cold water). The hot water at least I use for washing dishes is not hot enough to sterilize. Water heaters heat to about 120F, and 175F for several minutes is required for minimal sterilization. So washing dishes makes things clean by removing bacteria, not by killing them.

"If you kill stuff, the soil chemistry won't be affected. Well, the NPK
may increase, because those constituents in the soil organisms are
destroyed."

The reverse is true, since plants assume mostly (and preferentially) microbe metabolites. With fewer producers, there will be fewer nutrients. Ask yourself why plants, on average, spend 25% of their energy on root exudates (they spend a lot more during growth of course).

Further, fungi will not repopulate rapidly to the level of fertile soil. Mixed ecosystem studies suggest a time of order five years from field-wide disruption (like plowing). They are for sure still increasing exponentially two years after, even in pastures. Not having myc. does exactly the opposite of the intended to young plants, it creates water stress (and therefore susceptibility to disease) where a plant next to it, still attached to a myc. network, will not suffer.

Likewise, mineralized (available) nutrients in organic systems increase over the course of a decade. It will take a shorter time if the disruption is very localized (like strip till), but then why boil only a strip?

Nope. If you have a particular soil chemistry, as per NPK, with bacteria and fungi, and you destroy the bacteria and fungi, as in, disassemble them, the proteins contained within them will disperse into the soil and, if anything, add to the NPK, ideally in plant-usable form. The NPK that was there doesn't disappear! It would take some mysterious powers to make N, P, and K go away. But you're right that in the long run, without bacteria and fungi, you won't get more NPK produced.

This conversation started out asking about quickly sterilizing soil. I'm just saying that if you sterilize soil, the immediate result may be a slight increase in nutrient content. It will not be a decrease in nutrient content. No question that if you leave the soil sterile, nutrients won't be released. But that's not what we're talking about. In fact, soil that is quickly sterilized and exposed to unsterilized soil will fairly promptly get repopulated with bacteria and fungi. So unless you take the sterilized soil and seal it off, or have a residual in the soil that is a bactericide and fungicide, all will be made right pretty quickly.

Not sure if that's true about fungal population not repopulating rapidly. See here ...

http://www.soilhealth.com/soil-health/organisms/fungi-bact/

"In general, the greater the fertility of a landscape, the greater the
soil microbial biomass. The fungal population will increase at a greater
rate than that of bacteria, leading to a higher fungal-to-bacterial
ratio."

But maybe you have some better references?

I just looked at some recent data. Admittedly my bias is that old prairie soils have "ideal" ratios, and they have fungi/bacteria mass ratios of order 1. But plowed soils have ratios well below 0.1, and even after two years after pasture establishment they are below 0.1. Bacteria do the N, but they mineralize some P and K too (they have to, the plant is only providing sugars), and fungi do the humus, the P, and the water. They are generally stronger at mineralizing.

Both provide resistance to biological (disease) and non-biological (drought, heat, etc) stresses. Both help the plant energy efficiency, since for example both provide pre-formed amino-acids which the plant does not have to synthesize itself. Protozoa and nematodes eat them in the rhizosphere, and poop all those unneeded minerals (specially N since bacteria have a C/N ratio of 5).

Been busy at work, plus I am moving (but keeping use of both garden and orchard), I will see if I can dig up some youtube seminars with some numbers.

I think these are the two videos I had in mind

https://www.youtube.com/watch?v=GmgvmuaS644

starting at around 40:00

https://www.youtube.com/watch?v=lcPRYR_OKd0

starting at around 33:00

granted they discuss also soil issues related to grazing, but specially the second gives an idea how fast fungi populate from year to year after a disturbance.

What you have to be a little careful about is, in assessing population, talking about numbers of species. Fungi are LOTS larger than bacteria, so the biomass of fungi in soil is almost always larger than the biomass of bacteria, even though there are vastly more bacteria. I think this bears on the quote I gave.

I'm willing to believe that on very short timescales, bacteria can repopulate faster, because bacteria can reproduce in just a few minutes

Certainly bacteria are favored in highly disturbed soil. Tillage doesn't really kill fungi, but tears up the long strands that lets fungi easily "forage" for nutrients. So tillage does make it harder for fungi to survive. After tillage, you basically have the same biomass of fungi that you started out with. It's just in smaller pieces.

And, irrespective of anything I saw scanning above, the hot water would not 'sterilize' soil because many bacteria form endospores.

Ref; Bacterial Endospores | Department of Microbiology - '' Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include high temperature, high UV irradiation, desiccation, chemical damage and enzymatic destruction. The extraordinary resistance properties of endospores make them of particular importance because they are not readily killed by many antimicrobial treatments.'' The emphasis is mine.

Yes, endospores need something like 6 hours of boiling water and or heat with pressure, like an autoclave, to kill. But not all bacteria produce endospores. The thermophilic bacteria that predominate in hot compost do.

In fact, I think that's one reason why the safety of sewage sludge for composting is somewhat suspect. Regular Pasteurization doesn't work for some pathogens.

Actually, the very rapid rise in fungal mass shown in the first video can be interpreted as fungal mass being depleted by one tillage (pre-corn seeding), and then recovering at a fast rate but not getting where it would be in a mature diverse stand. The mass remains far below the bacterial mass after two years. My best guess is that a broken mycelium is severely weakened and has to spend resources to survive instead of expanding. My own shiitake, after all, fruit only after the organism reaches a certain mass. Keep in mind that in natural soil we have all phases present at the same time. There are predators, germination, and mature organisms at the same time.

But to summarize my own opinion about boiling soil in situ, it seems unlikely to achieve a positive outcome with any degree of confidence. If the conditions that attracted less useful bacteria are there, the site will be re-colonized by a similar flora. To the contrary, the best fix for bad bacteria is to feed good bacteria and let them compete.

Greenhouse owners and mushroom growers both use hot water and/or steam to sterilize the soil the use.

True, and I don't know exactly what the equipment looks like, but I bet they are not pouring boiling water on the ground to do it. Also they are probably not totally sterilizing it, just knocking down unwanted species?

I was thinking about doing the same thing, for small scale just a pot of soil which was infested with unknown insect or fungus, that literary rot and eats away my seedling within 24hrs after I transfer them to the small pot.

I have been pouring 2 rounds of hot water into it and it socked in hot water for like 15minutes? The soil looks more like clay... and water locked after I pour hot water into it.. I really don't know how it happen lol

I'd throw that in the compost and get some new potting mix if I was you.

Thanks to all who posted regarding the boiling of water and pouring over soil to sterilize. After nearly a month, none of my Tomato seeds germinated. The same can be said for Chinensis/tea tree seeds. But the Melon seeds and Cucumber seeds all seemed to germinate and are doing fine? Someone asked why would you sterilize the soil? In my case, my existing soil throughout yard is incredibly rich, but has become infected with Stinging Nettle and a variety of other weed seeds. I always use a portion of this soil to add in with Peat Moss and sand and steer manure-which I also treat with steaming. For those of you who haven't a clue why I would treat the steer manure, your lack of knowledge on treatment of cows is disparaging, at best. Those chemicals do come out in their feces though! Anyway, no matter the answers given, none of my small seeds germinated, so it appears I must simply add more soil and seeds and then pluck out the wild stuff that comes up with it-hopefully it won't crowd out the good seeds to quickly!

You goofballs, you don’t lug a large sloshing pot of boiling water out to your garden. It’s done in small batches for when you need soil for seedling trays or for putting soil in pots. If you’ve ever found yourself battling fungus gnats on your indoor plants, this is a surefire way to kill them off. They did tests on those little jur ks by placing them in -25F temps and 70% of them came back to life. Heat is what kills them off. That’s why you can subject them and their eggs to boiling water, steam or heat from a 180F oven. Both gnats, mold and bacteria can really hurt small seedlings and cuttings. They can also slowly deteriorate the roots on indoor plants. I sanitize my potting soil and I use hydrogen peroxide to clean my used pots before repotting them. Just because you buy soil that’s all bagged up in a store doesn’t mean that it’s not going to arrive without fungus gnat eggs already inside. Better to be safe than sorry.