Can You Put Potting Soil in Compost? (And in the Garden?)

Farmers turn to potting soil when growing plants in a container. Amazingly, there’s no soil in potting soil because the former substance is prone to carrying pathogens and fungus. So, if you favor potted plants, you likely have ample potting soil at home because this it’s one of the safest options for sensitive flowers.

Again, it won’t come as a shock if you’ve ever contemplated putting potting soil in compost. Well, you can add it to compost, but only when you’re confident it’s devoid of harmful organisms. It will also help if no flower has ever grown and died in it.

Adding potting soil to compost is slightly more challenging than you’d think. You’d have to pasteurize it, a process you’ll understand when you read this piece. You’ll also discover what you can do with old potting soil, so stay right there!

Can You Compost Potting Soil?

Composting is a reliable way to create ample nutrients for the soil and plants. It’s done under a controlled environment, with regulated moisture content and extended aeration.

The other parties that factor in are microbes and heat, and the former triggers the entire decomposition process – the heat picks up, and the fungi and bacteria create a network to break down.

Potting soil is fortified to improve the environmental conditions of potted plants. It contains every component required for healthy plant growth; however, it lacks soil.

This is because garden soil contains pathogens and some mildly harmful organisms that aren’t best for potted plants. But again, it’s sometimes inevitable for microbes like bacteria, fungi, and nematodes to find their way into potted or garden soil.

Potting soil qualifies as organic matter, and many believe it can be used to improve the quality or texture of the compost mix. However, before putting anything in your compost pile, ensure it doesn’t contain harmful creatures that can infect the future plants and soil the mixture will be used for.

You can compost potting soil. But if any plant has died in it, we recommend keeping it out of your compost pile. This is because there are high chances that the pathogens that killed the plant are equally present in the soil.

Adding it to your compost pile will only result in spreading the virus.

Is It Okay to Put Potting Soil in the Garden?

Potting soil is made of peat moss, compost wood, vermiculite, perlite, and mineral particles, to name a few. None of the materials here is harmful, so you can put potting soil in your garden.

However, most people fail to realize that a considerable amount of potting soil is required to fill a garden bed. Unless you have enough potting soil, it’s best to save that supply for something else.

How to Sterilize Used Potting Soil Before Adding it to the Compost?

Pests, diseases, and some harmful pathogens are commonly found in soil. Planting in this condition isn’t ideal because it can make your plants sick and die. So, to ensure maximum health for plants, it’s best to sterilize the soil before using it.

Before adding used potting soil to compost, you must also sterilize it. Even though it’s been created to grow plants in an environment devoid of harmful organisms, there are still chances that some pathogenic microorganisms are present there.

If you add it to your compost pile, it can pollute the materials. Since you’ll be applying the compost mix to your plants and soil, you’ll inevitably spread the pathogens.

So, you can:

1. Sterilize with steam

Sterilizing with steam is straightforward and exposes pathogens to extreme heat. You must steam the potting soil for about thirty minutes or until it attains a temperature of 180°F.

You can use a pressure cooker. However, we recommend showcasing extreme care when sterilizing nitrate-rich soil because it can cause an explosion.

Place several cups of water inside the pressure cooker and fill shallow pans with potting mix. Then, cover the pan with foil and leave the steam valve exposed long enough for steam to escape. Let it remain exposed for ten to fifteen minutes before sterilizing the next batch.

2. Sterilize with an oven

When you expose microbes to a temperature higher than 160°F, they die off. Whether they’re helpful or harmful, fungi and bacteria cannot survive in extreme temperatures, and you can maximize that by sterilizing your potting soil in a heated oven.

Ensure the temperature does not exceed 180°F because extreme heat can also introduce toxins into the potting soil. Leave in the oven for at least half an hour.

3. Use a microwave

Of course, this is a suitable option only if you’re sterilizing a small portion of potting soil. Place some in microwave-friendly containers and poke a few holes in them. Then, microwave for ninety seconds.

What to Do With Old Potting Soil?

Potting soil lacks pathogens and some harmful materials you may find in garden soil. The differences in structural composition make it impossible for all plants to thrive in garden soil, so we rely on potting soil.

However, this farming substance is sensitive and should be reused cautiously. The previous planting season’s past activities will tell on the soil, either through the presence of pathogens or harmful bacteria. Besides, all the essential nutrients in the potting mix would have been reasonably depleted, making it somewhat useless to potted plants that rely on it.

But again, the thought of wastefulness never appeals to a green thumb. So, here are four things you can do with your old potting soil:

1. As temporary soil

You can accumulate your old potting mix and use it as temporary soil. It has all the components of soil sans the nutrients. And since the soil will only be active for a short time, it won’t matter that the potting mix has already lost most of its nutrients.

This temporary soil can be used to gift plants to friends and family. It’s handy; a few scoops will be sufficient for each plant but don’t forget to provide transplanting instructions.

2. A new garden bed

A new garden bed would be an excellent addition to your backyard come spring. Making it is seamless too – introduce padding of newspapers or cardboard and cover the surface with the potting soil. Adding other organic matter will improve the quality of the soil and plants that germinate there.

Some of your options include dry wood shavings, grass clippings, kitchen waste, among many others.

You’ll have a supple garden bed with ample nutrients and fertility by springtime.

3. Store it for next season

If you have some used potting soil because your flowers didn’t make it through maturity, you can store it for the next planting season. Since the plants didn’t rely on the nutrients for a significant period, you can reuse them for your next attempt at planting potted flowers.

Now, do you recall how sensitive potting mix is? That’s the primary reason farmers avoid using it if it’s already served its purpose for a considerable period. So, store it in a sealed container to keep pathogens out. Otherwise, you may deal with sick plants the next planting season.

4. Inquire about yard waste drop-offs

Yard waste drop-offs are established to collect leaf and yard waste in many cities. It’s conventionally done in the fall and is an excellent way to dispose of plant waste and old potting soil.

The accumulated materials will be composted with the help of commercial composting machines and sold commercially.

What Should You Not Put in Your Compost?

Composting is an easily manageable way to transform your kitchen waste into black gold. This material is highly beneficial for plants because of all the nutrients from the individual items you put together.

However, you can’t compost every organic matter. Some of the items that you should not put in your compost include:

1. Protein Scraps

Meat and fish bones, and leftovers should never find their way into your compost pile. Although they give off a putrid smell while decomposing, they will draw every vermin within the area to the source. Even neighborhood pets sometimes dig through compost piles, searching for the aromatic source.

Closed compost piles aren’t entirely safe when you add protein scraps to the mixture. Unless you’re taking deliberate steps to keep pests away, it’s best to consider other waste disposal methods for meat and fish leftovers.

2. Dairy Products and Cooking Grease

Dairy products like milk, cheese, butter, and yogurt can also attract unwanted visitors to your compost pile. The same applies to cooking grease, mainly remnants used to fry meat, fish, or other protein.

3. Treated Plants or Wood

The last place any form of treated substance should be found is a compost pile. Most especially biodegradable household waste like wooden furniture, wooden fencing, and even plants that have been treated with insecticides or other harsh chemicals.

The toxic substances applied to these items will inevitably exude into the compost mixture. It pollutes the materials, which cause plant sickness or even death when used.

4. Black Walnut Debris

Conventionally, there are many green and brown options to add to your compost pile. However, the black walnut debris isn’t one of them because it contains a toxic substance called juglone.

This tree’s leaves, branches, and roots are poisonous to plants – they stunt and kill them in extreme cases. Tomatoes, potatoes, and pepper are examples of plants susceptible to harmful juglone content.

Although juglone eventually breaks down and loses its toxicity because of time and weather conditions, it’s best to leave this material out of your compost.

5. Infected or Dead Plants

It’s best to avoid composting infected or dead plants because the pathogens responsible will likely remain in their system. When you introduce it to the remaining matter in your compost, it can reinfect other plants on which you apply the composted mixture.

If you were relying on commercial composting, this wouldn’t be a challenge because the machines use great heat. Deadly pathogens won’t survive the extreme temperature, making it safe for future use.

6. Ash

Although ash contains some nutrients beneficial to plants and the soil, it’s only safe when you take it from a wood-burning fireplace or outdoor fire pit.

However, charcoal ash and coal are two materials you should keep out of the compost pile because of their high sulfur content. It increases the acidity for your plants, disturbing the balanced pH levels and causing further problems.

7. Dog or Cat Waste

Dog or cat waste is unsafe for a compost pile because they sometimes contain harmful bacteria. It’s a terrible idea because some of these bacteria can cause human infections too.

Cat waste is arguably one of the worst compostable materials because it contains a pathogen that causes toxoplasmosis. Pregnant women and unborn children are particularly susceptible to this disease.


Instead of throwing your potting soil away, there are many things you can use it for. Composting it is an excellent idea, but only when you’re confident that it lacks harmful microorganisms.

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About Rinkesh

A true environmentalist by heart ❤️. Founded Conserve Energy Future with the sole motto of providing helpful information related to our rapidly depleting environment. Unless you strongly believe in Elon Musk‘s idea of making Mars as another habitable planet, do remember that there really is no 'Planet B' in this whole universe.