Skip to main content

Knock out bugs, diseases, and more – Top tips for sterilizing potting soil

In order to grow most plants, you need soil. In many cases, you can just plant some seeds in the ground and watch them grow. For pickier plants, you can make your own soil mixes tailored to the plant’s needs. What do you do when your soil carries fungal spores or diseases, though? If you want to safely grow plants using it then you’ll need to sterilize it first. That may sound intimidating, but it’s actually quite easy. Here is how to sterilize soil and why you might want to.

Why should you sterilize soil?

Sterilizing soil isn’t necessary for everyone, but it can help if you’re using soil that has a history of diseases, pests, or fungal infections. If you aren’t sure about the soil’s history, then sterilizing it can help ensure that any harmful bacteria, pests, or fungal spores are less likely to impact the plants you grow.

Recommended Videos

Soil sterilization doesn’t kill everything. Those that are heat resistant or are able to multiply quickly may still survive the process. You can sterilize soil through heat or chemicals. Chemical sterilization is impacted by which chemicals you use. However, chemical sterilization can be hazardous to do at home, because of the potential health effects of the chemicals used. Heat sterilization is impacted by how hot the soil gets and how long it stays at that temperature.

Additionally, most methods are better suited to sterilizing potting soil. Traditional outdoor gardens simply have too much soil for most sterilization methods. While you could sterilize part of your outdoor garden, it wouldn’t have much of an effect. The best ways to sterilize traditional gardens is through solarization, simply letting it sit unused, or switching to plants that are resistant to the particular disease you’re dealing with.

A baking dish covered in tin foil
Image used with permission by copyright holder

Baking in an oven or microwave

To prepare your soil, place it in an appropriate container and moisten it slightly. The water will become steam, which helps evenly heat the soil. For ovens, spread the soil out in a layer that is 1 to 3 inches thick and cover the container with tin foil. For microwaves, use a microwave-safe bag or bowl that isn’t sealed or covered. Make sure there is no metal in your soil before placing it in the microwave!

The ideal temperature for this method is 180 to 200 degrees Fahrenheit. Use a meat thermometer or other easy-to-clean thermometer to measure the temperature of the soil itself. The soil should stay in that temperature range for 25 to 30 minutes if you’re using an oven.

Microwaves, which are used for shorter times, won’t be able to hold the temperature for that long. Instead, focus on getting the soil to that temperature range. The amount of time it takes varies depending on the strength of your microwave. Remember, the soil will be hot, so let it cool before you handle it.

A covered, stainless steel pot on a stovetop
Image used with permission by copyright holder

Steaming

You can steam soil in a pressure cooker or on a stove, but the method is more or less the same in either case. Start with a couple of cups of water in the bottom of the pressure cooker or a couple of inches of water in the bottom of a pot. Place a rack over the water, so the soil is just above the water rather than sitting in it. Place your soil in small heat-safe containers. The layer of soil in each container should only be a couple of inches thick.

Cover the containers with tinfoil. Put a lid on the pot, leaving a small gap for steam to escape. If you’re using a pressure cooker, leave the steam vent open, to begin with. Depending on the pressure cooker model, the valve may close on its own, or you may need to manually close it once the water heats up. Cook the soil in the pressure cooker for 15 to 30 minutes, and the soil on the stove for 30 minutes. Let the soil cool before removing it.

White plastic stretched over the ground, held down by bricks
Image used with permission by copyright holder

Solarization

Solarization, or using the sun to sterilize your soil, can be done on small or large batches of soil. The downside of this is that it takes much longer. All you need is clear plastic of a medium thickness, which is about 1.5 to 2 millimeters. Thinner plastic is more likely to tear, while thicker plastic can slow down the solarization process.

Remove rocks or debris from the soil and then break up any large clumps before starting. If you’re solarizing potting soil, then spread it out on a layer of plastic. Moisten the entire amount of potting soil or the top foot of your garden. Then spread another layer of plastic on top. Secure it at the edges with heavy objects, and wait four to six weeks in the summer, or twice as long in colder, cloudier conditions.

Sterilization can help protect your plants from pests, diseases, and fungal infections. It may even kill some weed seeds, reducing the amount of weeding you’ll need to do. While it can’t get rid of everything, it can be helpful if you’re reusing your soil. It’s an especially good idea to sterilize soil if plants grown in it before struggled with diseases or infections. Using these simple methods, you can sterilize your soil and grow your plants safely.

Cayla Leonard
Cayla Leonard is a writer from North Carolina who is passionate about plants.  She enjoys reading and writing fiction and…
Your complete sago palm maintenance guide
Grow a sago palm to add a tropical flair to your home
A small sago palm in a pot designed to resemble a wicker basket. It sits on a table of light wood, next to a bookshelf of the same wood. The wall behind it has a dacorative pink, blue, and white triangular pattern.

Sago palms may not be true palms, but they are just as gorgeous. However, with these subtropical houseplants, you won’t have the same kind of look offered by those tall trees. Instead, the green fronds grow directly from the trunk without branching out. Sago palm maintenance is fairly simple, relying mostly on proper growing conditions. Adding this lovely houseplant to your collection is an excellent way to bring the tropics to your home. If you want to grow your own today, this guide will explain everything you need to know to help it thrive!
Care requirements for your sago palm

Because they’re native to tropical regions, sago palms prefer to be in warm, humid environments. This is why, for the most part, they’re grown as houseplants outside of these areas. Sago palms grown indoors should be protected from any drafts or air flowing from heating and AC units as the extreme shift in temperature can cause damage.
Light
Sago palms prefer bright, indirect lighting and shouldn’t be placed in direct sunlight. Direct lighting, especially on hot summer days, can cause sunburn damage and result in wilting leaves. As a houseplant, sago palms will favor east-, west-, and south-facing windows so long as they receive a lot of lighting throughout the day. Keep in mind that too much shade will also cause adverse effects, most noticeably spare foliage.
Soil
Like most houseplants, sago palms need only well-draining soil (and of course, a pot with a drainage hole for excess water to escape through)! There are potting mixes made specifically for palms grown in containers, and although the sago palm isn’t a true palm, this should do the trick.
Water
As a tropical plant, sago palms prefer moderately moist soils. They can tolerate some drought, but not very well. Proper sago palm maintenance requires watering the plant whenever the soil is dry to touch; however, be mindful of how much you’re watering to avoid soggy soil and leaving your plant susceptible to root rot.
Diseases and pests to be aware of

Read more
What does NPK mean when it comes to fertilizing plants?
Your guide to the main nutrients in the NPK ratio for robust plant growth
A gardener fertilizing a young plant

Just like humans, plants need food to stay healthy and strong. Fertilizers give plants full-sized leaves, healthy roots, and vibrant flowers. Without sufficient soil nutrients, plants will grow very slowly, developing weak stems and pale leaves. Fertilizer helps make up for what the soil may be lacking, so that your garden has a balanced diet to grow and thrive.

When choosing your fertilizer, you might have noticed something on the label called an NPK ratio. If you're wondering what that means and how to use it to choose the best fertilizer for your plants, we have the answers.
What is NPK's meaning in plant fertilizing?

Read more
What exactly is loam soil? Here’s what to know
How to identify and create loam soil
Hands scooping soil out of a flower pot

Most plants need soil to grow in, but not all soil is the same. There are heavy, dense clay soils and loose sandy soils, as well as many soil types in between. Clay and sand are easy to identify, but a soil type that’s less straightforward is loam. Loam soil is something that many plants prefer, but unlike sand and clay soils, which are named after their main ingredient, loam is a bit more obscure.

So, what is loam soil made of, why do so many plants love it, and how can you make it at home? This guide to loam soil will explain everything you need to know.
What is loam soil?

Read more