How to sterilize soil: The ultimate guide for every treatment

How to sterilize soil: The ultimate guide for every treatment

Repeatedly utilizing the identical backyard soil or potting combine time and again can result in a buildup of weed seeds, fungal spores, dangerous pathogens, and different detrimental backyard pests. When you decide to reuse your soil repeatedly as an alternative of replenishing it, it’s in your finest curiosity to periodically sterilize it. This offers a clear, uncontaminated rising substrate on your vegetation.

What’s soil sterilization?

Sterilizing soil is a course of that has been finished in industrial greenhouses, and by agricultural producers for fairly a while. Greenhouses carry out it to save lots of them from replenishing their potting soil yearly; farmers sterilize their fields after they have pest or illness issues in high-dollar crops – sterilization is cheaper than treating issues or probably shedding a whole crop.

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Soil sterilization performs an even bigger position when soil is used for seed germination, the propagation of stem or shoot cuttings, and the transplanting of juvenile vegetation. These rising situations enhance the susceptibility of damping off and different plant issues if the soil is contaminated with mould, fungal spores, or different dangerous organisms. Soil sterilization is much less important when solely rising mature vegetation, however remains to be helpful when carried out periodically.

There’s a mixture of opinions on whether or not or not soil sterilization is critical and even good observe for owners and small scale gardeners to comply with.

Some imagine it isn’t well worth the time invested for what little advantages are seen; some are involved it negatively impacts the helpful elements of the soil, wiping out good micro organism and microorganisms; others imagine it’s important for good plant progress, particularly when gardening in containers or raised beds with potting mixes.

The reality is, execs and cons exist, relying on the strategy of soil sterilization used. Unfavorable ramifications could be minimized when procedures are rigorously adopted.

Methods to sterilize soil

There are two primary methodologies used to sterilize backyard soil and sterilize potting soil: chemical therapies and warmth therapies.

Chemical Therapies

This observe is utilized on a bigger scale, usually by industrial operations due to the price and hazards concerned with the method.

On the upside, chemical sterilization therapies are straightforward to make use of and software could be finished rapidly, even when sterilizing a considerable amount of mineral soil or potting soil.

There are some main drawbacks although, which is partly why chemical therapies aren’t as widespread, particularly with owners.

  • Chemical purposes pose a well being and security threat to the individual doing the appliance, and people in shut proximity.

  • Trendy chemical substances have a really slim vary for which results might be seen. Most often, a single chemical will solely eradicate one in every of a slight few ailments or pests.

  • After software, there’s a quarantine interval earlier than the soil can be utilized once more. That is needed to permit the chemical substances to degrade absolutely or be flushed out of the substrate.

  • If not utilized correctly, residues could linger within the soil and probably be taken into the vegetation by the roots, concentrating in plant tissues.

  • Lengthy-term use of chemical substances can enhance the resistance of a illness or insect pest to a given therapy, rendering it much less efficient and even fully ineffective over time.

Warmth Therapies

Resulting from lots of the unfavorable elements of chemical sterilization therapies listed above, warmth therapies are far more generally utilized by house gardeners.

Warmth therapies elevate the temperature of the soil by steam or direct, dry warmth to a threshold the place the dangerous organisms, fungal spores, weed seeds, and so forth. are unable to outlive, and die. Warmth therapy is commonly known as sterilization, however it is a misnomer because the soil isn’t fully sterile on the temperatures induced.

It does kill weeds and pests relying upon the inner temperature reached (1), and the size of time the brink is maintained. Most directions advocate no less than half-hour on the given temperature to kill particular organisms (see Desk 1) in moist soil or potting combine.

Analysis has proven that even sterilization considerably reduces the inhabitants of helpful soil micro organism, it doesn’t eradicate them fully. After sterilization, sure species resembling Pseudomonas and Bacillus, rapidly recolonize the soil and their populations attain excessive ranges inside a brief period of time (2). This fast recolonization overrides the preliminary discount in populations by sterilization.

Desk 1. Goal Temperatures for Soil Sterilization of Moist Soil Goal Temp Organisms Killed when Temp Sustained for 30-minutes 120℉ water molds (oomycetes) 145℉ most plant pathogenic fungi, micro organism, and viruses, worms, slugs, centipedes 160℉ plant pathogenic micro organism, soil bugs 180℉ weed seeds 212℉ warmth resistant plant viruses and weed seeds

Warmth therapies could be dangerous if the inner temperature of the substrate is allowed to get too excessive. Extreme soil heating could enhance the prospect of phytotoxicity resulting from soluble salts, manganese toxicity (3), and poisonous natural compounds.

Soil mixtureshigh in readily decomposable natural matter (manure, leaf mould, compost) usually tend to give harm when uncovered to excessively excessive temperatures than mineral soils or potting mixes the place the natural matter has fully damaged down.

Provides wanted for house soil sterilization

Relying on the strategy you select to make use of, your provide record will differ barely. General the next gadgets are issues you have already got in your house.

  • Baking pans or different heat-proof containers.
  • A thermometer able to studying upwards of 200℉. Meat thermometers work properly since they are often inserted into the middle of a mass of soil, and are straightforward to wash when you’re completed utilizing them.
  • Plastic wrap or aluminum foil.
  • Zip prime baggage.

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Strategies to warmth sterilize your soil

Selecting which technique to steam or warmth sterilize your soil is very depending on the quantity of substrate you’re working with, and the way rapidly you need the method finished. The 4 widespread strategies of warmth sterilization completely different primarily based on their warmth supply: boiling water/steam, a house oven, a microwave, or pure power from the solar.


Utilizing the pure warmth of the solar is a typical strategy to sterilize massive quantities of soil, particularly complete gardens or fields. The fundamental precept with solarization is soil is roofed with layers of plastic and left to soak up the rays from the solar, elevating the temperature over a time frame to kill off problematic pathogens, weed seeds, and pests.

Sterilization by solarization can happen in a few other ways. The strategies produce the identical outcomes; which one you select is a matter of desire and price range.

  • Massive scale gardens or fields are coated with plastic to lure the solar’s power.

  • Bigger portions of soilless potting mixes are unfold between a backside and prime layer of plastic to lure the photo voltaic power.

  • Smaller portions of both mineral or potting soil are positioned in plastic baggage and set within the solar.

Selecting what plastic to make use of

The kind and thickness of the plastic used for sterilization has some distinct benefits and downsides.

Clear or clear plastic is a more sensible choice than black for solarization. Black plastic deflects a few of the photo voltaic power as an alternative of trapping all of it as clear plastic does.

Thinner plastic (1 mil) permits for higher heating however is extra vulnerable to ripping by wind or animals. Medium thickness plastic (1.5 to 2 mils) works higher the place situations are windy. Thick plastic (4 mils or extra) ought to solely be utilized in small areas.

How you can solarize soil

No matter which particular technique of solarization you’re following and which kind of plastic you select, related primary steps must be adopted.

  1. Whether or not working with mineral soil or potting soil from containers, preliminary prep is essential to extend the effectivity of the warmth therapy. Begin by breaking apart all clods and eradicating litter from earlier vegetation.

  2. If you’re working with potting soil, lay down the underside layer of plastic and unfold the potting combine evenly excessive, staying no less than 6-inches away from the perimeters of the plastic.

  3. Irrigate the substrate till they’re barely moistened. Backyard soils must be wetted to a depth of 12-inches.

  4. Cowl backyard soils and potting mixes beforehand unfold out with a layer of plastic. Pull the plastic tightly throughout the soil floor, securing it with rocks or a layer of soil alongside the perimeters. If utilizing plastic baggage, fill them with soil and shut tightly, setting them in a sunny location within the yard.

  5. 4 to 6 weeks of solarization through the hottest a part of the yr must be ample to sterilize the soil. Areas with cooler, windy, or cloudy climates could also be upwards of eight to 10 weeks of solarization.

It’s believed that many helpful soil organisms are in a position to both survive solarization or they recolonize the soil in a short time afterward. Earthworms are thought to maneuver deeper within the soil profile to cooler areas. This leads to a sterilized soil that’s rapidly recolonized with each helpful soil organisms and useful earthworms.

Boiling water or steam

Steam is a good way to effectively sterilize your soil. It may be finished with or with no stress cooker. If utilizing a stress cooker be sure you comply with all the producer’s security precautions.

Strain cooker technique

  1. Fill the stress cooker with a few cups of water and insert the rack into the cooker.

  2. Set heat-proof containers on the rack above the water with not more than 4-inches of soil in every container.

  3. Cowl every container tightly with foil.

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    Place the lid on the stress cooker, leaving the steam valve open barely to permit steam to vent till the stress begins to construct.

  5. Modify the warmth supply beneath the stress cooker, permitting it to construct steam.

  6. When the steam valve closes, course of the soil at 10 kilos of stress for 15 to half-hour.

  7. Take away from the warmth supply and permit the stress to subside fully earlier than eradicating the lid.

  8. Maintain sterilized soil coated with the aluminum foil till it’s time to make use of.

Non-pressurized container technique

  1. Arrange your steam container by placing an inch or two of water within the backside of a non-pressure cooker; then place a rack within the backside of the sterilizing container.

  2. Set heat-proof containers on the rack above the water with not more than 4-inches of soil in every container.

  3. Cowl every container tightly with foil.

  4. Place a lid on the container, leaving it cracked barely to stop steam from build up.

  5. As soon as the water involves a boil, enable it to boil gently for half-hour.

  6. Take away from the warmth supply and permit the temperature to drop earlier than eradicating containers.

  7. Maintain sterilized soil coated with the aluminum foil till it’s time to make use of.


Sterilizing soil in your oven works properly you probably have small to medium batches to course of, and it poses much less hazard than utilizing boiling water/steam or the microwave. Consider although because the sterilization happens your kitchen might be stuffed with what could also be deemed an disagreeable odor. It’s finest to do that when you may open doorways and home windows for sufficient air flow.

  1. Add roughly 3-inches of soil to an over-proof container.

  2. Combine in sufficient water to totally moisten the soil, however not a lot that it turns into runny or overly saturated. An excessive amount of water will decelerate the method considerably. The water is required to create steam as it’s pushed off.

  3. Cowl the tops of the containers with aluminum foil and place in an oven preheated to 200℉.

  4. Monitor the inner temperature of the soil along with your thermometer. When it reaches 180℉, enable it to “bake” for thirty minutes with out opening the oven door.

  5. Shut the oven off and permit the soil to chill to room temperature.


Utilizing the microwave to sterilize your soil is an efficient possibility if you happen to solely have a small quantity of soil to work with. Fastidiously examine the soil earlier than inserting it within the microwave to verify it doesn’t have any steel in it.

  1. Place about two kilos of moist soil inside a clear zip-top, plastic bag. The soil shouldn’t be waterlogged or runny however damp sufficient it holds collectively in a clump while you squeeze a handful.

  2. Go away the highest of the bag open and place it within the middle of the microwave.

  3. Microwave on excessive till the center of the soil reaches a temperature between 180℉ and 200℉. The size of time this takes to attain will rely on how highly effective your microwave is.

  4. Fastidiously take away from the microwave, shut the highest of the bag, and place inside a cooler till the temperature naturally comes again right down to the ambient situations.


Soil sterilization eradicates dangerous organisms, weed seeds, and pathogens from mineral soil and potting mixes by chemical or warmth therapies. That is advantageous in situations the place soils are used repeatedly to germinate seeds, propagate cuttings, or develop juvenile vegetation. Offering a “clear” rising surroundings prevents damping off and encourages robust, wholesome progress. Quite a lot of warmth therapies can be utilized by owners to cheaply and effectively sterilize their soil.

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  1. Baker, Ok. F., & Chandler, P. A. (1957). The U.C. System for Producing Wholesome Container Grown Crops. College of California, Division of Agricultural Sciences, Agricultural Experiment Station Extension Service.
  2. Gamliel, A., Hadar, E., & Katan, J. (1987). Microbial phenomena associated to elevated progress response in solarized soils and to monoculture techniques. In: Proceedings of the seventh Congress of the Mediterranean Phytopathological Union.
  3. Fernando, D. R., & Lynch, J. P. (2015). Manganese phytotoxicity: new mild on an previous downside. Annals of Botany, 116(3), 313-319. doi: