After you have been growing potted plants for a while, you may see some green material on the potting soil.
The soil in your potted plant is turning green because there is algae, mold, or moss growing in it. These will grow in the soil because of too much moisture, humidity, poor air circulation, and decomposing material. Most of these are not dangerous to the plant but can still affect its growth.
I’ve written details below to help you get rid of the green growth from your potted plant and keep them away for good.
Is the green growth in the potting soil bad for your plant?
The green growth in the potting soil can be algae, mold, or moss. None of these will directly harm your plant.
Algae is an aquatic plant that grows on surfaces that are moist and have sunlight. There are many different species of algae, but they often appear green because of the chlorophyll in them. Algae will grow on the potting soil but not harm the plant.
Mold is a fungus that causes decay in organic items such as textiles, wood, and food. Molds are found everywhere, both indoors and outdoors. They can be white, green, brown in color. Most molds are harmless to the potted plant but some can harm them.
Moss is a non-rooting plant that grows on the soil in pots and garden beds. Moss is usually greenish in color, but it can be brownish, black, white, or silver colored. Mosses are not harmful to your potted plants because they do not absorb any nutrients from the soil. They gather sunlight to help their roots grow properly and send water through their leaves into their roots.
The problem with algae, mold or moss growing in the potting soil is they will compete with the plant for nutrients and moisture. The plant will not get the required resources to grow well and this will stunt its growth.
The other issue algae, mold, or moss will create is when they dry out and become hard. This will form a crust on the soil that will not allow water to penetrate well into the soil. Your plant will not get the required moisture causing it to be underwatered and leaves to turn yellow and drop.
Some mold can be toxic to humans and pets. They can also contain allergens that may cause reactions if you or your pets touch them.
How to get rid of the green material from your potting soil?
You can use the methods I mention below to get rid of algae, mold, or moss from the potting soil of your plant.
Scrape the material off the soil
The simplest method is to use some paper towels and clean the material from the soil’s surface. You could also use a spoon to scrape the material from the potting soil.
Make sure to use face and eye protection because some mold can affect your breathing if you inhale the material.
You can even remove an inch of potting soil from the top if you want to ensure that all green material is removed.
Use an antifungal spray to get rid of the material
You can use a natural antifungal remedy to eliminate the algae, mold, or moss from the potting soil.
One solution is to sprinkle cinnamon on the surface of the soil. This is a natural antifungal agent that will kill such green material.
You could also use a mixture of 1 part baking soda with 9 parts water and spray it on the potting soil to kill the green material.
Expose the potting soil to sunlight
You can place your potted plant in sunlight to get rid of mold from the potting soil. This will only work if the problem is due to mold growing on your plant in the shade. Algae and moss prefer sunlight to grow well.
If the plant is not sensitive to sunlight, expose the potting soil to sunlight for a few hours every day till the mold dies off.
If the plant is susceptible to intense light, you can take it out of the pot and spread the soil in sunlight.
Keep the soil in the sun for a few hours and you can replant the plant in it. Keep doing this for a few days till the mold has gone away from the potting soil.
Repot the plant in fresh potting soil
If nothing else works, you can re-pot the plant in fresh potting soil free from any algae, mold, or moss.
Tilt the pot and tap it gently so the root ball slides out. Remove the potting soil and dispose of it.
i the pot using 1 part bleach to 9 parts water to remove any algae, mold, or moss in it. Rinse well and allow the pot to air-dry.
Fill the pot with fresh potting soil and repot the plant. Water it well, and then monitor closely for any signs of new algae, mold, or moss growth.
How do you prevent algae, mold, or moss from growing on potting soil?
The best way to protect your potted plant is to prevent algae, mold, or moss from growing in the first place.
Prevent overwatering the potting soil
The algae, mold, and moss prefer moist environments. If the soil gets too moist due to overwatering, it will create conditions for the green stuff to grow.
You want your posting soil to contain moisture but you don’t want it to stay damp and moist. Water the potting soil only after it has dried out completely.
You can stick your finger 1-2 inches into the potting soil to check the moisture. If the tip of the finger is dry, it means that it has dried out and you can water.
Use the right watering method for the plant
I recommend watering your plant in the morning before the sun rises. This will help evaporate any excess moisture on the soil.
Put your pots somewhere where the sunlight can reach the potting soil. This will help it dry out sooner so that no humid conditions can develop in the soil.
It would help if you avoided spraying water on the foliage as this can lead to humid conditions that encourage mold, moss, or algae growth.
You can water the potting soil using a watering can. Make sure the pot has drainage holes at the bottom. Keep watering the soil till the excess water drains out from the bottom.
You may benefit by watering the plant from the bottom rather than the top. You do this by putting the plant in a saucer or tray filled with water.
The plant’s roots will absorb the water from the tray due to capillary action. This will help the plant have more control over the moisture in its soil. There will be no moisture on the top of the soil which helps avoid any green material growth.
Use good quality potting soil for your plant
Several issues can occur if you don’t use the right soil for your potted plant. Some people tend to use garden soil which can invite algae, mold, or moss to grow.
The garden soil can contain mold spores that can reach into the potted plant. The garden soil may also contain a lot of clay that can retain water and cause drainage problems. The longer the soil remains moist, the higher are chances of mold, algae, or moss development.
You should buy potting soil that is sterile and free from any such unwanted spores. This will help prevent algae, mold, or moss from growing in the soil.
Choose the right size of the pot
It would be best if you used a pot that is 1-2 sizes bigger than the plant. If the size is very large, the plant’s roots won’t absorb all the moisture and a lot of it will remain in the potting soil.
This will lead to the problem of overwatering where the roots are drowning in water. The excess moisture in the soil will invite fungal issues including root rot and mold. It will also encourage algae and mold growth in the soil.
If the size of the pot is enormous compared to the plant you bought, you can use filler material in the base of the pot. This will reduce the volume in which you can add the potting soil and protect the plant from overwatering.
Give the plant good growing space
Your plants need good growing space, especially when in a pot. If they are too close to each other, it will create humid conditions that attract algae, mold, and moss growth.
You should learn more about the type of plant you’re growing and the space it needs. Make sure to prune the foliage so there is good air circulation.
If the plants are growing very close to each other, you can take one out and transplant it to another pot.
If the plant is a vining variety make sure to give it good support in the pot with a stake or trellis. This will help the plant grow vertically instead of in the soil that can increase moist conditions.
Keep the potting soil clean
If debris like decomposing leaves and branches are in the potting soil, it can encourage algae, mold, and moss growth.
You want to keep your potting soil clean and allow enough air circulation so the soil surface can dry out in good time.
I recommend using mulch on the potting soil, which could be organic matter like dried leaves, wood chips, straw, or hay. This helps regulate the soil temperature and keep moisture in the soil longer.
But this can have the drawback of attracting algae, mold, or moss growth. So keep checking every couple of weeks for any signs in the potting soil.
Here are some of my favorite container gardening tools
Thank you for reading this post. I hope it helps you with your gardening needs. I’ve listed some tools below that can help you with container gardening. These are affiliate links so I’ll earn a commission if you use them.
Gardening Gloves – I find the Pine Tree Tools Bamboo Gardening Gloves really good for both men and women. It’s made from bamboo so helps absorb perspiration. They are also comfortable and fit very well.
Containers – You know picking the right container is crucial for your container gardening. I’ve written a detailed post on the best containers you can choose from. If you’re happy with a plastic container, you can check out the Bloem Saturn Planter.
Watering Can – This is a must-have tool when you’re growing plants in pots or grow bags. It helps to water the potting soil without splashing on the foliage. The Kensington Watering Can is stylish, strong, and can provide precision when watering potted plants.
Trowel – Garden Guru Trowel is my favorite because it’s durable and comfortable to use. My gardening friends really love having a trowel because they use it for digging soil, mixing fertilizer, moving seeds, leveling out the soil, mixing compost or mulch, and also dividing tubers
Bypass Pruner – I really like the Corona Bypass Pruner because it’s durable and gives a clean cut that helps plants recover faster. If you’re looking for something cheap, get the Fiskars Bypass Pruner that is really good as well.
To see an extensive list of the best container gardening tools gardeners recommend, check out this resource that I made for you.
Kevin is the founder of Gardening Mentor, a website that aims to teach people to grow their own food in a limited space. As a self-taught gardener, Kevin has spent several years growing plants and creating gardening content on the website. He is certified in Home Horticulture and Organic Gardening by expert gardeners from Oregon State University.