One of the most common reasons why soil may begin to smell is due to anaerobic activity. This can be caused by various factors, such as heavy bad aeration or overwatering.
Potting soil can smell bad because of factors such as bad drainage and lack of oxygen which leads to the anaerobic decomposition of organic material. This can lead to the production of bad-smelling gases such as ammonia and hydrogen sulfide. Soil should have an earthy scent and any variations from this should be checked.
Garden and potting soil can contain an array of soil mixes that can all work together in providing the plant with optimal nutation, drainage and aeration.
In this article, we are going to outline the different causes of why soil smells whether it is potting or garden soil and what you can do to curb if not eliminate the odors once and for all.
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What Causes Potting Soil to Smell bad?
Break Down of Organic material In the Soil
Degradation of organic waste by anaerobic organisms produces highly odorous gases and other compounds including hydrogen sulfide (H2S), ammonia, volatile fatty acids.
The release of these compounds, especially hydrogen sulfide, in the immediate surroundings has the potential to cause a considerable nuisance.
This is usually caused by underlying soil issues such as bed drainage and soil aeration. Bad drainage can be caused by anything from a plant being rootbound to a bad soil mix which has limited space for the water to drain through.
A ripple effect of high water retention, apart from root rot, is bad aeration which is the root cause of anaerobic synthesis.
Good drainage and Soil aeration are attributes of healthy soil and fixing these two things can totally eliminate the problem of smelly soil.
Potted Plants that Contain Peat Moss
Peat moss may seem as a good option for soil but over time it can get a bit smelly.
When used as a soil amendment peat moss does not add any nutrients to the soil but it does hold moisture which is a good thing for thirsty plants.
However, the problem here is not the soil moisture but the pungent odor it may emit.
The problem is that it has a pungent odor, the smell of earth and peat moss. In fact, it can be quite overwhelming if you use too much.
It’s fairly normal for peat to start smelling like sulfur as it ages. Normally it isn’t too noticeable until it comes time to repot. And I don’t think it poses any specific threat to plants, but it does indicate that the soil is becoming anaerobic.
Therefore, peat moss is not an ideal option for indoor plants.
How do you Fix Smelly Soil
The first step in eliminating the odor is by adding more air space between the soil particles with mixing in soil amendments to occupy some of the air space.
Smelly soil can be fixed by adding soil amendments such as perlite and vermiculite to the mix in order to increase the aeration and drainage properties of the soil. When added, soil amendments would increase the air spaces between soil to soil particles while providing a pathway for water to drain freely.
Usually it is the first 2 to 4 inches of the soil that has the most amount of organic material and also the most amount of microbes and bacterial activity. This is why topsoil is also dark in color for most cases. A lack of oxygen within the soil’s top layer can cause it to smell really bad.
Dealing with smelly soil would therefore mean unearthing this layer of topsoil in order to rectify the problem.
Here are some easy tips on how to reduce this unpleasant smell in your garden.
Mix in Activated Charcoal In the Soil
Gaseous chemicals (Hydrogen sulphide and ammonia) stick to the surface of the activated carbon until the filter surface is fully saturated.
The carbon contains thousands of small pores within its structure which attracts and removes foul gases from the air with a process known as adsorption.
Although this is an effective method of eliminating the bad odors, it will not stop it. Eventually when the activated carbon is saturated, the smell will return.
But don’t fear, We have some more permanent fixes. Read on!
Remove Rocks from the soil
Using a shovel or a rake, gently till away the first few inches of the topsoil.
If you have unearthed some rocks with your trowel, store it in a separate container.
Add additional soil back into the mix to make up for the spaces that the stones have taken up.
The removal of rocks will help prevent soil compaction and open up air spaces in the soil for better drainage.
Remove Roots old Roots from the soil
Another reason for bad drainage is that the soil is filled with dead roots. Roots when left in the soil after a harvest or a growing season can cause drainage problems in the upcoming season.
Old roots rot and add a strong bad smell to the soil. It is important to remove old roots.
To do this, you can use a root picker or a small shovel, which you may buy in a gardening store. Just remove all dead roots from the soil. The more, the better.
See our detailed article on weather or not you should leave dead roots in the soil.
Add soil Amendments
Adding soil amendments like perlite or vermiculite can help increase the drainage and aeration in the soil. These soil amendments can help with bad smell from the soil.
Perlite and vermiculite are minerals that can be used as an additive for potting soil. They are very light material that increases the drainage and aeration of the soil. It can also improve the soil’s structure and make it more solid.
Adding perlite, vermiculite or sand to the potting soil will improve the drainage and aeration of the soil, which will improve drainage and reduce odor formation in the future.
For more detailed instructions on how amendments like vermiculite can benefit your soil see or detailed article on soil amendments here.
What Does Good Soil Look like?
Good soil would have a dark appearance which is the result of organic matter degrading. It may have some food for the plants like some mineral fertilizers as well which would be a good sign.
Avoid buying soils that contain chemicals because it will do far more harm than good.
There are many different types of soil mixes but for a healthy plant growth, good soil should have these properties:
1. Holds Optimum moisture Levels
Good soil will hold just the amount of water that is needed for nutrients to gain mobility from the soil to be absorbed by the plant. When the water content is too low or too high, roots can’t grow and are healthy. They would either not grow or develop root rot.
2. Does Not have Weeds
Good soil will keep weeds at bay because your plant doesn’t have to compete with its own roots for nutrients.
Good soil can be made of many different things. [Soil may have multiple elements: sand, clay, chalk, etc.]
3. Has Good drainage
Good drainage means that the water drains away from your plants quickly. It will also keep roots from drowning in too much water.
4. Has Good Aeration
Good soil should have the right amount of air pockets for your plant to breathe. Oxygen, for plants, is essential because it makes the process of respiration more efficient.
It is also needed by the bacteria and other microorganisms in the soil for converting organic matter into nutrients for the plant.
Top 5 Ingredients To Make Good Soil:
1. Organic Matter
Organic matter is the most important ingredient in good soil. It is responsible for holding water and nutrients in place making it available to the plant.
Organic matter contains decomposing bacteria which help break down poor quality soil, adding valuable nutrients and improving drainage. By adding compost or rotted manure, you are providing your garden and potted plants with a healthy home and helping them thrive.
Compost is a very important part of your garden soil. It helps retain water, improves soil drainage and adds essential bacteria to the soil. It improves the quality of your soil and keeps your plants healthy.
Gravel is inexpensive, easy to work with and excellent in increasing drainage. Adding gravel increases aeration in your soil and provides a good structure for drainage. This enhances root growth by allowing air and light to penetrate the potting mix, which encourages healthy roots to grow.
4 . Sand
Sand prevents drainage problems, improves soil structure and increases the amount of air in the potting mix. Sand will provide more nutrients to your plants as it adds mineral nutrition back into the soil.
This is because sand typically is very sterile and will not hold much water. Adding sand increases aeration and provides enough oxygen for beneficial aerobic bacteria to break down organic matter in the soil.
Clay is one of the most important ingredients in building a good soil. It helps retain water, supplies minerals to the plant, improves drainage and helps plants absorb nutrients.
Clay also contains bacteria that assist in breaking down organic matter. It creates a healthy environment for the plant and often is called “living soil”.
However, The most important thing to remember about your soil is that it needs to suit your plants needs and conditions. What might be good for one plant might not be right for another.
Soil can smell bad from the anaerobic breakdown of organic material under the first few inches from the surface. This is a sign of good bacterial action, but not a sign of good drainage and aeration.
Adding a few soil amendments to the mix can help you get rid of the smell. Adding perlite and vermiculite will aerate the dirt while also providing pathways for water drainage, which is key if you want to stop that nasty odor from coming out of your soil.
Additionally adding activated carbon can get rid of the problem while you seek a better way in providing a good soil mix for your plants.