Why Does Your Soil Look Like Ash? 5 Possible Reasons

Maybe you check your plants every morning or are more of a once-a-week plant parent. Either way, you may wake up one day to find your soil looks like it’s been burnt in the night. Gray, sooty soil that looks like ash can signify something happening to your plant. 

If your soil looks like ash, it could be covered in fungus or mold. Or, the soil could be soggy, have a high sulfur content, or contain mildew. There are also some soil types that just naturally look ashy. It’s possible your soil is one of those, especially if you’re new to gardening.

Below, we will discuss the cause and symptoms of each possibility. We will also give you some DIY fixes for each problem and a look into what healthy soil should look like.

1. The Soil Is Covered in Fungus or Mold

Ashy soil might look gray, be soft to the touch, or remind you of soot. However, you probably have a fungus on your hands, which is more common. Gray fungus and mold are prevalent in plants, and while some aren’t harmful in the least, others can ruin your plant’s health.

It’s more typical to find this gray mold on the roots and leaves of your plants, but it’s possible to find them in the soil as well. It’s most common in wet or humid conditions and can be caused by a change in your watering routine or overwatering.

Additionally, it could be caused by drainage issues.

Knowing the Difference Between Harmful and Harmless Fungi

Mold is a type of fungus that has a pretty bad reputation. You don’t want mold in your home, on your bread, or likely anywhere near you, but the fungus is excellent for plants. We know that fungi can live in harmony and even have a symbiotic relationship with our house plants.

If you have a gray mold or fungus in the soil, it could be a mycelium or saprophytic fungus. Some gardeners work hard to cultivate mycelium in their gardens to help plants absorb water and nutrients

This video by Desert Plants of Avalon shows a visual of what this harmless fungus might look like:

But if you’re noticing something more nefarious, you should go with your gut. If you’ve determined that it’s not just your soil that looks like ash, but your plants that look covered or are developing rips, tears, or holes due to a gray substance, this is likely a mold problem. Sooty mold can damage your plants and may even indicate an insect infestation.

A gray mold taking over your plant leaves, petals, or roots is an entirely different beast, though. 

You should be able to tell whether you have a gray mycelium or a gray mold by seeing how your plants have been affected. If they seem to be doing well or even better, you likely have healthy fungi. Otherwise, while there may be several other issues, you should do some more investigation on the substance.

To tell the difference, you’ll have to look at pictures of both and compare them to what you’re seeing. Unfortunately, there’s no tell-tale sign like a scent or a texture that will send you one way or another.

Fixing A Fungi Problem 

If you find that you have a harmful fungus in your garden, you have a few options. You can:

  • Repot the plant in fresh soil with a green pot, getting rid of as much of the old soil as possible and then sanitizing it or tossing it.
  • Remove the mold with garden gloves and use natural fungicides on your soil. 
  • Be wary of your watering routines, utilizing a moisture meter or another tool to ensure you’re not overwatering.
  • Put your plants in a sunny place and space them out to make sure they dry entirely after watering.

Hopefully, the ashy gray soil you found is just an indicator of the fungus that can help your plants or give you a hint that you’re overwatering. Otherwise, you should consider taking as many action steps as possible to save your plant, isolating it from other plants until it’s doing better.

2. The Soil Is Soggy

Soggy soil may cause the gray, ashy substance in your pot. 

If you tend to overwater your plants or water them before they completely dry out from their last shower, you could be keeping your plants’ soil soggy. As mentioned above, soggy soil can lead to fungus, mildew, or compaction. 

It could also indicate drainage problems in your plant.

The gray soil on top of your plant may be just the beginning of the problem–eventually, this can lead to root rot and a plant that will no longer grow.

How To Know If You Have Soggy Soil

Though you may think it’s pretty straightforward, you should do some thorough checking to see if you have soggy soil. Noticing soil that’s wet and soppy is the most obvious indicator, but having soil that’s hard and compact will also be a sign you’re overwatering. 

Some plants require drying out thoroughly before they are watered again. 

If your watering habit doesn’t let your plants dry thoroughly, you’re essentially drowning them with water. Plants need time to absorb water before they get another dose.

Fixes For Soggy Soil

If it’s become compacted, soggy soil may be too far gone to continue using. You may consider repotting your plant in healthy soil and using a moisture meter to indicate whether or not your plant is getting enough moisture. 

Moisture meters can also sometimes detect sunlight, humidity, and pH so you can see if you have other problems going on.

You’ll also want to read up on your plants to see what they prefer. Just like humans, all plants are different. Some like to dry out completely, while others might enjoy full rain showers every other day. 

Knowing the difference and writing it down on a placard or having it in a notebook until you can remember may save your plants from becoming oversaturated.

You could also begin composting or mulching in your soil to help absorb extra moisture if the overwatering occurs naturally. Compost and mulch in a thin layer will add healthy microorganisms to your soil in addition to supporting moisture saturation.

If you have the time and resources, setting up drainage or an irrigation system in your garden might also be helpful.  

3. There’s a High Sulfur Content in the Soil

If you’ve noticed that your outdoor gardening area has been overtaken with gray, ashy soil and there are no indications of mold, you may have a high level of sulfur

Grays and blues in soil tend to indicate a high sulfur content. While gray ash indicating a high sulfur content is more common in your outside garden, there’s a possibility it could happen with your household plants, too. 

How To Know If You Have A High Sulfur Content in Your Soil

While a shift in nutrients can happen naturally, it most commonly happens at the hands of a gardener. Some of us will add high nitrogen or sulfur soils to support our plants’ growth or fix the soil pH which might go too far. 

Testing your pH or sending a sample into the lab are easy ways to figure out what’s going on in your soil nutrient-wise. 
Another cause of sulfur in gardens is pollution. If you live in a high-traffic area and are worried your garden may face the consequences of pollution, a rising sulfur content may indicate that pollution affects your plants.

Fixes For High Sulfur Content 

To displace excess sulfur, you should consider fertilizing, composting, or mulching your garden. You can add another type of soil to your garden that doesn’t have sulfur in it, such as something higher in other nutrients.

Additionally, you could increase your drainage and irrigation efforts to ensure what isn’t being used is being flushed out efficiently rather than just sitting in your soil. Or, you could create a plant repotting rotation, where you replace the soil and clean the leaves and pots of your plants for worries about pollution.

4. There’s Mildew in the Soil

Mold can go either way, healthy or unhealthy, but mildew is usually harmful. Gray mildew will likely be more a part of your plant’s leaves, roots, and petals rather than its soil. 

However, you should still be cautious, and research powdery mildew just in case. Mildew thrives in excellent, wet conditions and can attack your plants whether they’re indoors or outdoors. If you find that the gray mildew is more a part of your plant than your soil, you should immediately treat the plant for mildew.

How To Prevent Mold From Growing in Your Potting Soil

Although mold in your potting soil can be very frustrating, there are preventative measures you can take to stop future bacterial growth from infesting your soil. 

The first thing to consider is how frequently you’re watering your plants. If you’re not watering them enough and they live in a poorly-ventilated area, this can create ideal conditions for mold to grow. 

However, overwatering your soil can also have the same effect of creating a damp, humid environment that mold loves. You should be testing your soil before you water it, and if the top layer of potting soil is completely dry, it could do with some water.

Otherwise, try to resist the temptation to drown your plant and the potting soil in water. 

Additionally, your potting soil container should have an adequate drainage system. This means that excess water can easily seep out, rather than festering inside the soil and creating a haven for bad bacteria. If your container doesn’t have drainage holes, replace it with one that does. 

If your plant is kept in a dark environment, try moving it out somewhere brighter. 

Mold adores those dank, humid places, so if your plant is in the sun, mold won’t grow on the soil. This basic preventative measure also means your plant will enjoy much more natural sunlight. 

Finally, you should consider regularly removing any dead organic matter that falls onto your potting soil, which can include leaves and small branches, both of which will begin to decompose once it has hit the soil. 

The decomposition of this organic matter will attract mold spores and fungus, so try to clean up the soil occasionally if your plant regularly throws leaves around. 

How To Get Rid of Mold in Potting Soil

Mold is usually the cause of gray potting soil, so knowing how to get rid of it permanently is essential. 

If you’ve got spare potting soil mix lying around, sometimes the best thing to do is repot the plant completely. Doing so places your plant in a new, healthy environment without fear of contamination from the old potting soil. 

However, repotting will only work if the mold hasn’t worked its way up to the plant’s leaves. If any leaves on your plant have little fluffy pieces, this is mold. You’ll need to prune your plant and carefully snip off any infected leaves. 

Some say cinnamon is the best way to remove mold or fungus in potting soil, as it is antibacterial in its natural form, and is completely harmless to the soil itself, so it might be a good idea if you’ve got any at home. 

Using cinnamon alongside baking soda, another antibacterial substance will give you the best chances of getting rid of the mold or fungus. 

Follow the steps below to get rid of mold on your potting soil if you don’t want to repot your plant:

  1. In a small bowl, mix 2 tsp (9.86 ml) of ground cinnamon with 1 tbsp (14.8ml) of baking soda. 
  2. Add a few drops of water until the mixture is watery. 
  3. Pour the mixture into an old spray bottle.
  4. Spritz the affected areas on your potting soil and leave for a couple of days, spritzing once in the morning. 

If you follow these instructions for a few days, the mold or fungal infection should disappear.

5. It’s Just a Type of Soil That Looks Ashy

While I assume most are looking for some guidance on soil that’s turned to ash overnight, there’s also a possibility that a new gardener or someone who has adopted a plant has found that the soil is gray like ash without any indication of problems. Some soils are just gray, ashier, and look like soot. 

A naturally gray soil may indicate high glauconite or quartz minerals. It could also indicate overwatering and removing iron and manganese pigments in the soil. Furthermore, it could’ve been caused by a plant being grown near or in gravel before making its way to you.

Why Your Potting Soil Is Gray 

You may not realize it, but your plants need iron to thrive and gather energy from the sun. The primary place they’ll get their all-important iron supplements, along with all the other nutrients they need, is through the soil.

If your soil is gray, this might hint at a bacterial infection. Some types of bacteria will dive deep into your soil and suck out the nutrients meant for the plants, pulling out essential iron supplements, as well. 

Additionally, your potting soil might look a bit ashen because it has a layer of mold over the top. You’ll be able to see this mold quite easily, as it looks a bit like a spider’s web over the topsoil and might look fluffy. 

Mold indicates that there is too much decomposing material in the soil. 

Finally, another reason your potting soil might be gray is because of a fungal infection. Many types of fungus aren’t harmful to your plants, but their presence may still be a telltale sign that something in your potting soil just isn’t quite right. 

Most soils have some measure of fungal material within them, which is often a good indicator of healthy soil. However, some varieties of fungus will play havoc with the delicate ecosystem of your potting soil, creating fluffy, damp areas of the topsoil that are leeching crucial nutrients from the soil. 

What Color Should Your Potting Soil Be?

Most potting soils will be a mixture of organic matter, amendments, and basic soil, which means that, more often than not, your soil will be brown. The healthiest soil is dark brown in color, and the darker the color, the more organic material, which is called humus

If your potting soil is a nice dark brown, this means it contains enough nutrients to happily house your plants. If your potting soil is lighter in color and becomes yellow or white, this can often mean that it has been leached of nutrients. 

Adding a few soil amendments or a handful of compost can do the trick to turn that soil’s smile upside down. 

Signs of Unhealthy Potting Soil

Knowing the signs of unhealthy potting soil is a good indicator of how well your plants will do in the soil. More often than not, the soil will let you know when it’s not feeling its best, usually by smell, color, and a few other things. 

Let’s look at these in more detail below:

  • The most convenient way to see if your potting soil is unhealthy is to see if it smells bad. A foul-smelling soil indicates over-absorption of water and over-decomposition of organic matter. If you’ve used too much compost in your soil or it’s expired, it will likely smell a bit like sulfur. Lack of adequate drainage can also make your soil smell bad.
  • The presence of bugs can indicate unhealthy potting soil. Little flying creatures will attack decomposing organic matter in the soil, leaching out essential nutrients and making the soil incompatible with life. 
  • Putting too many soil amendments in your potting soil can offset its natural balance. Peat moss, in particular, tends to decay relatively quickly. This means your potting soil might become too dense to support your plant roots. You’ll be able to tell if you’ve put too much peat moss if your soil feels very hard to the touch.
  • Your plants aren’t doing well despite proper care. If you’ve been looking after your plants properly and they’ve suddenly wilted or died, the potting soil might be the problem. Your plants will often be the first ones to tell you their soil isn’t good anymore. 

How To Improve Unhealthy Potting Soil

The only way to improve unhealthy potting soil is to have the correct balance of soil, organic matter, and fertilizer. Organic matter is an excellent soil amendment, and it’s relatively inexpensive to make yourself at home. 

However, be careful not to add too much organic matter to your soil, or you’ll upset the delicate natural balance of the soil.


An ashy, gray soil can mean any number of things. Retrace your gardening steps and try to remember if you’ve done anything differently to your plant, as it can be an indicator of what the cause was. 

Typically, gray ash is a mycelium fungus that means no harm to your plant and can even help it absorb water and nutrients. However, if it’s harmful fungi, mildew, or an indicator of soggy soil or sulfur content, you will need to take action steps to save your plant and get your soil back to optimal health.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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