Have you ever encountered this situation: You have just purchased a bag of soil for your plants. When you opened the packaging, you were greeted with a bad smell and moldy soil. Usually this means a bad batch of soil from the manufacturer, but before you throw the whole thing away, there’s actually a solution to this!
If you want to avoid this situation entirely in the future, check out our trusted soil manufacturers for succulents here. They guarantee good quality control over their soil, which means less headache and frustration for us.
What is the Best Soil Sterilizer?
If you notice that your soil contains powdery mildew or other fungi, the best option is to use a fungicide or soil sterilizer. The best soil sterilizer and houseplant soil fungus treatment we’ve ever used is this Liquid Copper Fungicide by Bonide:
Bonide 811 Copper 4E Fungicide 16oz (473ML)
- Controls plant diseases – Liquid Copper Fungicide helps control powdery mildew, downy mildew, black spot, peach leaf curl, rust, and many other listed diseases.
- Protection for plants – Designed for use on listed vegetables, roses, fruits, nuts, herbs, ornamentals and turf.
- Organic gardening – Approved and suitable for all of your organic gardening needs. It can even be used up to the day of harvest. This natural fungicide is designed to be safely used around people and pets.
- Contains copper – The active ingredient of liquid copper is copper octanoate, or copper soap. Copper is a naturally occurring chemical which makes it a great option for use on all of your plants.
- Easy to apply – Product instantly mixes with water and should be applied using either a hose-end sprayer or tank sprayer. Carefully read and use, according to label directions.
If you do not wish to use a fungicide, there are many ways to sterilize soil. We discuss all of them in this article.
Can Potting Soil Go Bad?
To prevent potting soil from going bad, the correct storage method should be used: an open sack of potting soil should not lie outdoors, as the rain flushes the nutrients out of the soil. The humidity will also change the acidity of the soil. Pests will seek shelter in the open soil bag, and weed seeds will invade the soil, which will produce seedlings that consume the soil nutrients.
Properly stored, i.e. closed, cool and dry, potting soil lasts about twelve months. After that, it loses nutrients, but is still optimal for weak-eaters (plants with low nutrient requirements). For heavy or medium-sized eaters (plants with strong or medium-strength needs), the potting soil should be enhanced with compost or a long-term fertilizer before use.
Yellow Mold in Plant Soil – Is it Harmful?
There are different types of mold and fungus that can cause yellow growth on the surface of your soil. Although yellow growth is usually not going to harm the plant, it does give the soil an unhealthy look.
If you notice yellow fungus in your garden soil, it is actually Leucocoprinus birnbaumii, also known as Lepiota lutea, that frequently grows on the potting soil surface and often turns into large , bright yellow mushrooms. The fungus typically grows in commercial potting soil, and is completely harmless.
What are the White Balls in my Plant Soil?
Often mistaken as the eggs of insects, the white balls you find in potting soil is actually perlite. Perlite is a naturally occurring volcanic glass that resembles small white balls made of plastic foam. It is often used as a soil amendment because it has high permeability / low water retention and helps prevent soil compaction.
How to Sterilize Potting Soil in the Oven or Microwave
If you want to use cheap soil from the supermarket, old soil from last year or garden soil, we’ll show you here how to kill potential pests and already existing mold spores.
Sterilizing soil works best with heat. This can be achieved either by baking soil in oven or even faster in the microwave. All you need are these:
- sufficient amount of soil you want to sterilize
- an oven-proof or a microwave-friendly vessel
- some water
First, you should moisten your soil well. When you squeeze the soil together, it should retain its shape but not drip like mud. In both cases of the oven and the microwave, it’s faster if you spread the soil flatly on a metal tray. As a result, it heats up faster.
In the microwave, 5 to 10 minutes should suffice at the highest level. Halfway through the time, you should mix the soil.
In the oven you need a little longer. One or two cake trays full of soil should be baked in the preheated oven for 20 minutes at 392°F (200°C).
Let the soil cool completely afterwards and moisten it again before you put it in the pots for planting.
Sometimes after heating you can see some white particles or worms that you couldn’t see before. These are insects such as mites or larvae and worms: they consist mostly of protein, which denatures (clotted) in the heat and turns white. Once or twice we were surprised after sterilizing the soil, seeing how many larvae were actually present in the soil, which weren’t discovered before because of their brown color.
How to Sterilize Soil with Boiling Water
If you do not wish to put soil into your oven for hygiene purposes, you’d be interested in knowing how to sterilize soil without baking. There is an alternative to baking soil, which is to use boiling water. This is a very effective method for pest control and soil diseases although more cost and effort is required.
The steps to follow are as follows:
- Prepare the soil as for planting, making sure it is completely dry.
- Boil clean water in an appropriate container.
- Water the dry soil with the hot water, submerging it until about 5cm to 15cm deep.
- Cover the treated surface with a layer of polyethylene or plastic, to preserve the soil temperature for longer.
If watered to a depth greater than recommended, there is a risk of destroying nitrifying bacteria in the soil, which can lead to elevated ammonia content and increased soil toxicity.
Do You Always Need to Sterilize Soil?
It’s harmless to sterilize the soil, but it is not always necessary. To find out it the soil is mixed with harmful spores or germs, you can perform the cress test:
- Fill a pot with some of the soil, which will later serve as growing soil.
- Slightly moisten the soil.
- Then sow cress.
- Then place the pot in a bright and warm place and wait.
If the cress germinates within about three days, is well rooted and looks healthy, the soil does not need to be sterilized in order to use it as a growing soil. The germ content is then low and does not damage young plants. If, on the other hand, the cress does not germinate, this is a clear sign that the soil contains too many germs, fungi or spores.