Why is my Plant Soil Turning Green?

Why is my Plant Soil Turning Green? (5 Tips To Fix It!)

Plant soil turns green due to algal and moss growth caused by excess moisture. This happens when these organisms find an environment rich in moisture and limited sunlight. Understanding the role of moisture and the growth patterns of algae and moss helps explain why your plant soil is turning green.

What is green stuff on plant soil?

The green stuff you see on plant soil is either green algae or moss. Moss looks fibrous or feathered while algae don’t grow any thread-like structures. Algae look slimy and grow on wet surfaces.

You need to be able to differentiate algae from moss to efficiently get rid of either of these.

If you touch moss, it’ll feel springy. Algae grow due to excess moisture in the soil and excess humidity.

Is Algae bad for plants?

Yes, Algae significantly harm the growth of plants. Algae actively compete with saplings/plants for nutrients and water.

How do Algae affect plant growth?

Algae slows down the gaseous exchange into and out of the soil thus slowing down root growth. Plants don’t survive in such conditions.

In addition to this, Algae attract gnats and shore flies. Gnats and shore flies like to feed on the roots of a plant. While doing so they also transfer a variety of diseases from plant to plant.

Basically, Algae disturb the growing medium by interfering with the nutrient intake of your plants. It’s better to prevent algal growth in your potted plants.

How to get rid of Algae in potted plants?

Follow the below instructions to get rid of Algae in potted plants.

  • Moderate Watering: Avoid overwatering to prevent excess moisture, a breeding ground for algae.
  • Sunlight Exposure: Place plants in well-lit areas to discourage algae growth, which thrives in shade.
  • Regular Cleaning: Remove debris and dead leaves from the soil’s surface to prevent moisture retention.
  • Natural Remedies: Use diluted Hydrogen Peroxide or cinnamon powder on the soil to deter algal growth effectively.

Mold in plant soil harmful to humans?

No, mold in potting mix/plant soil is not harmful to humans. These algae release spores that are quite harmful to infants. So, if you have an infant child, be careful and try to prevent mold in your garden/indoors.

If there’s a big mat of mold in your pot, it has spread wildly and you need to replace the pot before the plant becomes susceptible to root rot.

Ingestion of these spores causes deficits in the learning and motor skill of your child. So, keep such plant pots as far from children as possible.

Mold does compete with saplings and unestablished plants for nutrients.

How do you kill algae without killing plants?

Follow the below instructions to kill algae without killing your plants.

Does vinegar kill algae?

Yes, Vinegar can kill algae. Vinegar is a natural way to get rid of algae for good. You won’t be adding any extra, unwanted chemicals to the soil/potting mix.

Mix one part of Vinegar in three parts of water. This solution can be spot-sprayed on algal growths to get rid of them.

This Vinegar solution is not at all harmful to the plants that surround the algae. Try to spray this solution only on the algal growth.

Can baking soda get rid of algae?

Yes, baking soda can be used to get rid of both algae and moss. You can sprinkle baking soda on algal patches and rub them using a brush.

Baking soda will loosen up the algal growth then you can scrape it off. You can also mix baking soda in water and use this solution to spot-spray algal/moss patches.

So, as you can see Vinegar is a better option if you want to get rid of algae for good.

What stops algae from growing?

You can mix 1/2 teaspoon of charcoal in the potting mix. This makes the soil sweeter and prevents any algal growth.

There are also other ways to achieve this, let’s see what those are and how to do it!

Mixing in sand

When freshly planting your plant, make sure that 1/4th of your potting mix comprises river sand (Don’t use construction sand as it may contain cement).

This helps enhance the draining ability of the potting mix. So, your potting mix will no longer hold more water than the plant needs leaving no room for algal growth.

Tip: Fill the bottom inch of the pot with gravel. This ensures that the roots don’t rot but still excess water is collected.

Replacing the soil

Replace the soil/potting mix quarterly to prevent algal growth. I’ve tried this and it works wonders. Take out the soil without disturbing the roots and replace it with fresh soil.

It is a good opportunity to add some compost to the soil. Spread out soil in the sun for a few hours before you use it in pots.

Don’t overwater!

Overwatering is the main reason why algae grow in pots. Moist conditions favor the growth of algae and moss.

Watch your watering schedule carefully and see if the plant is being overwatered. Check the soil with fingers and water only when the top 2 inches of the soil is dry.

If the water is dripping/exuding out of the draining holes then you’re probably overwatering the plant.


Whenever you are reusing pots, sanitize them thoroughly. Clean them with a chemical sanitizer or heat them to kill off any algal spores.

This might take some time to do but it saves a lot of time and pain down the line.

Light green mold on plant soil

The light green mold you see on your plant soil is likely caused by a saprophyte. This is harmless algae and grows in nutrient-rich soil.

The growth of saprophytes in your pot is a good warning of root rot. So, if you see saprophyte growth in your pots, reduce the amount of water you give your plant.

Small green eggs in soil

Those small green egg-like things you see in your pot are probably fertilizer leftovers. Check the ball-like structures to see if it has any fertilizer left in it.

If the nutrients in those green balls are extinguished, you just discard them. Such green balls are usually slow-release fertilizers.

If you are sure that it is not slow-release fertilizer then the ‘balls’ are probably some kind of eggs. In that case, vacuum/brush them off your pot.

Happy Growing 🙂