How to Sterilize Potting Soil

It’s a mix of field soil and soil amendments (e.g., compost, aged manure, peat moss, perlite, sand) where the living organisms have been eliminated usually by heat. These organisms include bugs (and their eggs) and microbes.

You sterilize it to prevent bugs from crawling or flying out of the potting soil and taking up residence in your home. It also prevents weeds from growing in the potting soil.

The best, most natural way to sterilize soil is to heat it to the point where it kills all living things in the mix.

No. A lot of potting soil is for outdoor use. So it is not sterilized. It is usually better for the plants if natural microbes are in the soil. Beneficial microbes help plants digest nutrients.

To sterilize potting soil, you need to heat it to 180 degrees Fahrenheit for 30 minutes. There are also chemical methods that I don’t recommend.

Sterile soil is less likely to (1) cause plant diseases, (2) harbor plant damaging insects and (3) grow weeds. However, sterilization also kills beneficial microbes and may make it more difficult for plants to obtain the nutrients needed.

Indoor potting soil is not sterile unless the manufacturer says it is. But sometimes the manufacturer will take steps to reduce troublesome insects like fungus gnats.

Commercially available potting soil is better for mature plants that need relatively high amounts of nutrients. Consequently, it contains more manure, compost and often fertilizer. Seed starting soil (a.k.a. seed starting mix) is designed for, as the name implies, growing seedlings. It is lighter than potting mix so that new roots and stems can move the soil around. It has more light weight materials like peat moss, coir, vermiculate and perlite. One more important point, seed starting mix may have some fertilizer in it to fuel the young plants. But most has very little. Young seedlings don’t need fertilizer when they start out because they get the nutrients they need from the seed itself.

You will often get bugs flying or crawling around your house. You may also get weeds or mushrooms growing next to your plants. Finally, there’s a better chance that your indoor plants will catch diseases from the soil. But all that being said, your plants may actually do better with non-sterile soil because it may contain beneficial microbes that help with nutrient uptake.

Most of the time, commercial potting soil makers will formulate it for containers, so it will allow water to pass through it more easily. Potting soil also will resist compaction. This is achieved by corse ingredients such as perlite.

Yes it will help. Sterilizing potting soil is one of the best ways to prevent gnats from taking up residence on your indoor plants.

No, potting soil has too many nutrients and is too heavy for young vegetable seedlings. There is a higher chance that seedlings will be affected by dampening off. That said, you can still be successful using potting soil for seedlings. It’s just that seed starting mix is better.

Seed starting mix is a lot lighter than potting soil. This is much better for your new seedlings. Seed starting mix also has less compost and fertilizer, which isn’t needed and could cause dampening off. It’s better to use seed starting mix rather than sterile potting soil.

One way is to make sure that all your seed starting mix and the potting soil you use to transplant the seedlings is sterile. Once you have gnats already, you may want to read how to Get Rid of Gnats on Vegetable Seedlings.

Most of the time, there are not enough gnats on your plants to do damage. But if the infestation is large enough, fungus gnat larvae can feed on the roots of your plants and impact the health of your seedlings.