Why Does My Potting Soil Turn Green? (DO This Now)

by Alex Kountry
Updated on

You’re not the only one who has noticed that the soil or seed starting to mix in your garden or greenhouse is becoming green.

This is a common issue among gardeners, whether they’re working in the dirt or starting seeds indoors.

So, what’s the matter with your garden’s soil?

It is common for algae to form a green coating on top of the soil, which flourishes in warm, wet, light, and moist settings. Algae thrive in soil that is exposed to a lot of sunlight and remains damp owing to excessive irrigation. High humidity fosters rapid growth in algae, which is why they are so common in greenhouses.

Without damaging your plants in the process, there are techniques to get rid of algae and keep it from returning.

Why Does My Potting Soil Turn Green?

Why Does My Potting Soil Turn Green

Your potting soil turns green because of algae, mold, or moss.  These will grow in the soil as a result of excessive moisture, humidity, poor air circulation, and decomposing organic matter.

While the majority of them are not harmful to the plant, they might nonetheless have an effect on its growth.

Algae is a type of aquatic plant that thrives on damp, sunny surfaces.

Algae come in a variety of kinds, however, they are frequently green in color due to the chlorophyll they contain.

Algae will grow on the potting soil but will have no adverse effect on the plant.

Mold is a type of fungus that degrades organic material such as textiles, wood, and food. Molds are found in virtually every environment, both indoors and out.

They come in a variety of colors, including white, green, and brown. While the majority of molds are innocuous to the potted plant, some can be harmful.

Moss is a non-rooting plant that grows in pots and garden beds on top of the soil.

Moss is typically green, but can also be brownish, black, white, or silver in appearance.

Mosses do not pose a threat to your container plants because they do not take up nutrients from the soil.

They collect sunlight to assist their roots in growing appropriately and send water to their roots via their leaves.

The issue with algae, mold, or moss growing in potting soil is that they will fight for nutrients and moisture with the plant.

The plant will lack the necessary resources to grow properly, hence stunting its growth.

Algae, mold, and moss also cause problems when they dry out and become hard.

This results in the formation of a crust on the soil, which prevents water from penetrating deeply into the soil.

Your plant will be deprived of necessary hydration, resulting in it being drowned and its leaves becoming yellow and dropping.

Certain types of mold are hazardous to people and animals. Additionally, they may contain allergens that may trigger problems if you or your pets come into contact with them..

Is Green Growth Bad for Plants?

The green growth is not exactly but they have an effect on plants. Algae, mold, or moss can all grow in the potting soil.

None of them will have an adverse effect on your plant.

How to Get Rid of This Green Growth?

Algae, mold, and moss in your plant’s potting soil can be removed using the methods listed below.

  • Scrape out the substance

Clean the soil’s surface with a few paper towels and you’ll be done in no time. To remove the dirt from the potting soil, you might alternatively use a spoon.

Use eye and facial protection, as some mold can impair your ability to breathe if inhaled. To verify that all green stuff has been removed, you can even remove an inch of potting soil from the top.

  • Apply antifungal 

Antifungal medication can be used in the potting soil to get rid of the algae and mold. Cinnamon can be sprinkled on the soil’s surface as a possible remedy.

Such a green substance will be killed by this natural antifungal agent.

To get rid of the green stuff, you might sprinkle the potting soil with a solution of 1 part baking soda to 9 parts water.

  • The potting soil should be exposed to sunshine.

To get rid of mold in the potting soil, position your potted plant in direct sunlight. Only if the problem is caused by mold developing on your plant in the shadow will this remedy be of any help.

To thrive, algae and moss need direct exposure to sunshine.

Sunlight can be used to kill the mold on the potting soil for several hours each day, provided that the plant is not sensitive to it.

Take the plant out of the pot and place it in direct sunlight if it is sensitive to bright light.

You can replant the plant after exposing the soil to the sun for a few hours. Keep doing this for a few more days until the potting soil is mold-free.

  • Repot the plant with fresh potting soil

If all else fails, try re-potting the plant in clean potting soil that hasn’t been contaminated by algae, mold, or moss.

This is your last resort. The root ball should slide out of the container by tilting it and lightly tapping it. Remove and discard the potting soil.

Using 1 part bleach to 10 parts water, sterilize the pot to get rid of any algae, mold, or moss. Make sure the pot is well cleaned and let it air dry.

Repot the plant after adding fresh potting soil to the container. Monitor it closely for signs of new algae, mold, or moss growth after it has been watered well.

How to Prevent Algae and Moss from Growing on Potting Soil

The following are some methods for preventing algae growth.

  • Use Potting Mix during Seedlings

If you are going to start plants from seed indoors, be sure to use potting mix from the store, instead of compost or garden soil (“dirt”) from your yard. 

Otherwise, you may bring in algae or spores from outside.

You need to be especially careful when growing in a greenhouse since algae spores on dust or dirt can be blown in by the wind.

If you see algae on the soil, try to dry it out or cover it to prevent it from spreading.

  • Don’t use Peat Moss, Perlite, & Vermiculite

These materials retain lots of water. 

This means that any growing medium that contains peat moss, perlite, or vermiculite will stay moist and will encourage the growth of algae.

  • Don’t Over-Water Your Plants

Before watering your plants, wait until the soil’s surface is completely dry. Algae thrive in soil that is constantly wet near the surface.

Consider raising your soil if it doesn’t drain well (such as with a mound or berm). Raised beds, grow bags, and other containers can all be used to elevate the soil for better drainage.

Is Algae Bad for Plants?

The presence of algae on your plants isn’t necessarily a bad thing, as it isn’t a parasite or a disease.

Nevertheless, there are a few ways in which algae can indirectly hurt or destroy your plants.

An algal bloom can cause your plants to lose moisture and nutrients in the soil, for starters. Algae can build a hard, black crust on the soil after a long period of time.

Water will be unable to reach the soil and the roots of plants if this crust remains for an extended period of time.

Even if you irrigate carefully, you may see the water “settle” on top of crusty green or black algae before it flows.

On the other hand, if you have a heavy coating of algae on your soil, it could cause mold or disease to your plants.


There you have it. Green substances can grow on your potting soil however, your daily maintenance settings will help prevent it now.

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About the author

Alex Kountry

Alex Kountry is the founder of HayFarmGuy and has been a backyard farmer for over 10 years. Since then he has decided to write helpful articles that will help you become a better backyard farmer and know what to do. He also loves to play tennis and read books


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