Do you sometimes wonder about the soil’s condition after using it for years? I have been using the same beds and potting soil for a long time. My focus has been on soil fertility, but of late, I have been wondering about pathogens and if soil sterilizing affects nutrient availability.
Sterilizing soil doesn’t remove nutrients. Instead, it increases the availability of macronutrients, such as nitrates from dead microorganisms. However, it creates nutrient imbalances that affect uptake and utilization. It also destroys good microbes, which distribute nutrients in the soil.
I’ll discuss soil sterilization in detail, why you should do it, how, when, and how often. I’ll also analyze the impact of soil sterilization on plants.
Impact of Sterilizing on Soil Nutrients
The main aim of soil sterilization is to eliminate pests, weeds, and diseases. However, it also affects soil nutrients.
- Sterilization destroys harmful organisms that inhibit nutrient distribution through the soil.
- It also releases blocked nutrients within the soil structures, resulting in higher nutrient availability and uptake.
- Good and bad microbes are destroyed during the sterilization process. Fortunately, good microbes break down and increase the nitrates in the soil.
- Nitrogen-fixing bacteria die and release the accumulated nitrogen compounds into the soil. This boosts soil fertility naturally.
- It destabilizes microbial colonies and activities in the soil. The rapid changes give beneficial microbes an upper hand, resulting in healthier microbial activities, which increase nutrient availability in the soil.
- It quickly breaks down organic matter, releasing more nutrients into the soil.
- It increases the availability of soil nutrients.
- It also creates nutrient imbalances, which affects uptake and utilization. For example, phosphorus, calcium, and magnesium concentrations fall after exposure to high temperatures during the sterilization process.
Soil sterilization kills most, if not all, living organisms in the soil. It also destroys pathogens and diseases, giving plants a fighting chance now that they can access nutrients without interference.
Should You Sterilize Soil?
Over time, soil toxicity and exhaustion affect plant growth and production. Plants start growing slowly, and you spend so much time and resources fighting weeds and diseases. It is usually time to consider soil sterilization when your efforts fail to have a lasting impact.
You should sterilize your soil because pests and diseases that build up in the soil affect nutrient uptake and plant growth. Soil also has pathogens, fungi, and harmful bacteria that kill plants or lead to stunted growth. Ultimately, poor nutrient uptake makes plants less competitive against weeds.
Soil sterilization creates a clean slate upon which plants can grow. Since weed seeds are destroyed during sterilization, plants get the opportunity to thrive without the risk of being overwhelmed by weeds.
When To Sterilize Soil
Soil sterilization is a great way to reset garden soil and make it productive again. However, although sterilization is good for the soil and plants, timing is equally important. You need to know how and when to sterilize the soil.
You should sterilize soil when:
- It has been in use for a long time.
- Pests and diseases keep attacking your plants.
- Moving dirt from your garden to pots.
- You have repeatedly used the same soil to germinate and grow juvenile plants.
- Using unsterilized store-bought potting mix.
- Preparing soil for the planting season.
Plants benefit from sterilized soil. Additionally, newly planted seeds and seedlings have a better chance of survival if growing in sterile soil.
How Often You Should Sterilize Soil
Plants thrive in sterile soil. They exhibit vigorous growth and an expansive root system. After sterilizing the soil, it will be some time before you need to do it again. You also don’t want to keep destroying beneficial organisms when the soil conditions are still ideal for plant growth.
Fortunately, some beneficial bacteria, like Bacillus and Pseudomonas, recolonize quickly. Their populations grow faster and to levels higher than before sterilization.
Only sterilize your soil periodically. Wait until weeds, pests, and diseases become a problem before sterilizing the soil again. However, it would help if you sterilized nursery beds more often because seedlings are more vulnerable to larvae and weeds, which often overwhelm them.
Is Sterilized Soil Better Than Unsterilized Soil?
Critics of sterile soil argue that sterilization kills all living things in the soil, including beneficial microorganisms. Sterilization also creates a nutrient imbalance. However, sterile soil has its benefits.
Sterile soil is better than unsterilized soil because it is less likely to have weeds. It is also free of pathogens and is unlikely to spread diseases. Plants grow faster and healthier in sterile soil than those growing in unsterilized soil because they encounter fewer problems.
As mentioned, plants flourish under sterilized soil. Typically, harmful bacteria and viruses multiply rapidly, negatively affecting plants. So, even though sterile soil has little or no beneficial living organisms, it is still better than unsterilized soil that’s contaminated with problem-causing organisms.
How To Sterilize Soil
After using the same soil repeatedly, it is normal for weed seeds, harmful pathogens, and fungal spores to build up. Insects also lay eggs, turning the soil into their breeding ground. This makes it challenging to get rid of pests and diseases, no matter how often you use pesticides or insecticides.
Soil sterilization is done using two primary methods, chemical, and heat treatments.
Chemical Treatments
Chemical treatments are ideal for large areas. Commercial sterilization treatments involve using chemicals because they are faster and cost effective. Unfortunately, the use of chemicals for soil sterilization has its drawbacks.
- The chemicals pose health risks to those applying them.
- You cannot use the soil immediately after the treatment. The chemicals need to degrade fully before the ground is ready for use.
- The chemicals will not eradicate all the pests and diseases.
- If the application is done improperly, plants may take in the chemicals and retain them in their tissues.
- Long-term chemical treatments will increase pest and disease resistance, making the chemicals less effective.
Heat Treatments
Home gardeners commonly use heat treatments. This involves exposing the soil to dry heat or steam at temperatures where fungal spores, weed seeds, or harmful organisms cannot survive. Most harmful organisms are eradicated when exposed to high temperatures for at least 30 minutes.
| Ideal Temperature | Target Organisms |
| 120°F (48.9°C) | Water Molds (Oomycetes) |
| 145°F (62.8°C) | Pathogenic fungi, bacteria, viruses, worms, and slugs. |
| 160°F (71°C) | Bacteria and soil insects. |
| 180°F (82°C) | Weed seeds. |
| 212°F (100°C) | Heat-resistant viruses and weed seeds. |
When soil temperatures get too high, phytotoxicity is possible due to the presence of soluble salts and toxic organic compounds.
This video gives tips on how to sterilize soil using heat.
There are four heat treatment methods you can use to sterilize the soil.
Steaming
To sterilize the soil via steaming method, take the following steps:
- Use a pressure cooker or regular saucepan to boil water.
- Place soil in heat-proof containers and cover them tightly with foil.
- Place a rack in the saucepan, then put the containers over it.
- Cover the saucepan or pressure cooker and allow the water to boil for 30 minutes.
- Steam the soil until the temperatures fall.
Home oven
If using a home oven:
- Moisten the soil, but don’t oversaturate it. The water will create steam as the temperature rises.
- Pour the dirt on the tray or ideal containers for the oven. Cover with aluminum foil.
- Place the soil in the oven, preheated at 200°F (93°C). The perfect soil temperature is 180°F (82°C). Bake the soil for 30 minutes before switching off the stove.
Microwave
If using a microwave, ensure the soil has no metals before placing it in the microwave. Then,
- Wet the soil and put it in a ziplock bag. The soil shouldn’t be runny, but it should clump.
- Leave the ziplock bag open and place it in the microwave. Heat until the soil temperature gets to 180°F (82°C).
- Remove the bag, zip the bag and allow the soil to cool.
Solarization
This method is ideal for small and large quantities of soil. Solarization involves using natural heat over soil covered with layers of plastic. The temperature underneath the plastic rises over time, killing pathogens, pests, and weed seeds. You can use a thermometer to keep track of the temperature.
Conclusion
Soil harbors unwanted pests and diseases, which affect plants, cost you time, and money. If you fail to sterilize your soil occasionally, you will be stuck in a cycle of plant diseases and pests, no matter how often you treat the plants.
Soil sterilization will give you and your plants a break from pests and diseases. Even though it causes an imbalance in nutrient levels, you can quickly replenish lost nutrients by adding compost or slow-release fertilizer.
