Whenever you decide to grow plant life in pots, be it small vegetable plants, flowers, or any other greenery, you want to be sure that your soil is full of rich nutrients your plant can use to grow and thrive. Many people use soil conditioners to help improve both the physical qualities and the nutrients within the soil. If soil conditioner improves both of these aspects and is added to regular soil, can you just use soil conditioner instead of potting soil?
You cannot use a soil conditioner as a replacement for potting soil. Soil conditioner can and should, be used as a supplement to potting soil, but it cannot completely replace the potting soil. Doing so would make the soil too rich in nutrients, which can harm plant life by reducing water intake.
While most people understand the importance of having rich soil, many people don’t quite understand why or how soil can be too rich. Stick around to learn more about soil conditioner and why it can’t completely replace soil.
Why You Cannot Replace Potting Soil With Soil Conditioner
Soil conditioner is generally good for plants so it might be surprising to hear that it wouldn’t make a good replacement for soil. However, to understand why this is, it’s important to understand how potting soil and soil conditioner work.
Potting Soil Explained
Imagine that it’s a hot, dry, sunny summer day. Along with the other daily chores, you decide to water both your potted plants as well as your garden. You’re afraid that your soil isn’t getting enough moisture, so you stick your finger in both the potting soil and garden soil to check.
While both have plenty of moisture, you pull your hand back and realize that the soil in your pots feels very different from the soil in your garden.
If your first thought is to be concerned, don’t be!
Potting soil is actually completely different than the garden soil found in the ground. Also known as potting mix, it is a blend of organic matter like compost, bark, moss, peat, and other substances that are specially designed for your potted plants.
Garden soil, alternatively, is real, actual soil.
Soil comes in different forms but generally contains organic matter as well as sediment, traces of clay, stone, and sometimes sand. All soil contains at least some organic matter, several microorganisms, minerals, and water.
The difference between garden soil and potting soil is that potting soil doesn’t actually contain any real “soil” and has no microorganisms in it.
Why would someone use this? The reasoning is actually very clear once it’s explained.
Potting soil is designed for small plants not yet ready to be in the ground or plants that are too delicate to thrive in the ground. To give these small and fragile plants their best chance, potting soil is completely sterile, meaning it has no microorganisms like fungi or parasites that might kill your plants.
Soil Conditioner Explained
While potting and garden soil has several differences, they also have many similar properties. Both potting soil and garden soil are, theoretically, full of nutrients that plants can use to make energy and grow tall and strong.
Soil, being made of so many different elements, has different textures and thicknesses, which means that it’s not completely even in every spot. But what happens if your soil is too thick in some spots or if it’s too thin in other spots?
What happens if your soil lacks the nutrients your plant needs to survive? This is where soil additives come in.
Soil additives, as the name implies, are mixtures of substances that you add to your soil to improve it. Some are designed to fix one issue with your soil, while others fix many issues with your soil, which is exactly what a soil conditioner is.
Soil conditioner is a type of soil additive that helps improve the soil’s nutrients and structure. Good soil normally is about 50% organic material, 25% water, and 25% air. It’s designed to bring soil to these guidelines by aerating and moistening the soil it is mixed with.
Imagine a brick house that has some holes and spots that are too small for a brick to fit in. In this analogy, soil additives push the bricks together in some spots so that the bricks can fit in the small holes while also filling in some of the holes with nutrients plants need.
Soil Conditioners Can Alter Soil pH Levels
Most plants require soil with a neutral pH level, which can range from 6.5 to 7.5. Some plants, including blueberry bushes, require more alkaline than acidic soil.
Whatever the ideal soil level for your garden, most soil conditioners will alter the pH level of your soil.
When you add a small amount of soil conditioner to your potting soil, the normal pH of the soil will balance out the conditioner. However, using soil conditioner on its own can result in dramatically high or low soil pH levels.
When the pH of your soil gets outside of the acceptable range, it can also lead to nutrient deficiencies.
Soil Conditioners Can Cause Nutrient Deficiencies
There are 17 essential nutrients, and plants need all of them. Since each nutrient contributes uniquely to a plant’s health, a deficiency in just one can have a profound effect. When the soil pH exceeds the acceptable range for a specific plant, it will not provide the proper nutrients for the plant to survive.
Different levels of nutrients exist at different pH levels. At a neutral pH of 7, there is a sufficient amount of every nutrient.
As the pH drops and the soil becomes more acidic, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium levels decline. On the other hand, alkaline soil, which is soil with a higher pH, contains less iron, manganese, phosphorus, and boron.
Even if you add nutrient supplements, your plants will not be able to absorb them if the pH of the soil is either too high or low. Therefore, if unbalanced pH levels cause nutrient deficiencies in soil, the situation becomes very difficult to fix.
Nutrient deficiencies can result in:
- Stunted growth of plants and produce
- Weak limbs
- Shriveled, discolored leaves
- Rotting produce
- Plant death
Since soil conditioners often do not contain all the nutrients that plants need, they cannot support plant life independently, so they cannot be used as potting soil.
Soil Conditioners Can Cause Nutrient Toxicity
Although nutrients are essential for the healthy growth of plants, too many nutrients can be equally harmful.
Nutrient toxicity occurs when the levels of a nutrient become too high.
The first sign of nutrient toxicity often takes place in the leaves of plants. Since there are not as many noticeable signs of nutrient toxicity as there are for nutrient deficiency, nutrient testing is important to address the issue before it becomes irreversible.
Toxic levels of one nutrient can also cause deficiencies in other nutrients because plants can only absorb a limited amount of nutrients at any given time.
If the plants take in too much of one nutrient, they won’t have the room or ability to absorb enough of the others. This often means that plants get most of the macronutrients they need but get cut off from the micronutrients, which are less numerous but equally important.
Using soil conditioner as potting soil puts plants at risk of dangerous nutrient toxicity. Although nutrients are necessary, remember that there can be too much of a good thing.
Why Potting Soil is Better than Soil Conditioner
While soil additive sounds like it must be the best thing ever in gardening (it is pretty good!), soil conditioner can also cause some issues if used incorrectly. Generally, it is good to be generous when using soil additives.
However, even though soil conditioner is good, too much conditioner can actually harm your plant life. As a result, you definitely can not use it as a replacement for potting soil.
The biggest reason for this is that, if soil conditioner were to be used as a replacement for potting soil, your plants would die. Plants take in the majority of their nutrients through their roots making them critical to plant growth.
Imagine them as little highways for plant nutrients. What would happen if the highway was completely blocked by 18-wheeler trucks? Traffic would stop, and people wouldn’t be able to get to their destinations.
The same is true with plant roots.
The nutrients, being the 18-wheeler trucks, would block important elements like water and air from getting to plant cells and plants wouldn’t be able to photosynthesis. The nutrients in plants are much larger than the compounds of water and oxygen, meaning that they literally block the way for these particles.
The other major reason that soil conditioner can’t be used as a replacement for potting soil is the fact that it isn’t strong enough to support the plant. Plants, like people, need solid footing in order to grow.
Soil conditioner is too thin for plants to stably grow without some sort of potting or garden soil.
The Purpose and Limitations of Soil Conditioner
Soil conditioner contains additives that address certain issues. The Soil Science Society of America classifies it as a kind of soil amendment that’s used in conjunction with soil. It’s either mixed in or layered on top of the soil.
Most soil conditioners are natural and used as an alternative to chemicals. Some natural materials used as soil conditioners include:
- Compost
- Vermicompost
- Wood chips
- Peat moss
- Coconut husks
They are often used for the following purposes:
- Increasing nutrient levels.
- Improving the soil texture.
- Improving soil water retention or drainage.
- Decreasing soil erosion.
Since soil conditioner corrects specific problem areas in your soil, it’s not well-balanced. As such, it can’t provide everything a plant needs to survive as it lacks some essential nutrients, which is why it can’t be used as potting soil.
Also, a soil conditioner on its own does not provide the ideal environment for your plants. If a plant is exposed to too many nutrients, it may not be able to absorb the necessary nutrients in the right quantities.
Identifying Problems With Your Soil
As noted, soil conditioner is primarily used in response to a particular issue., which is identified through nutrient testing. For information on how to perform nutrient testing on your soil, check out my article: Does Soil Need to Be Dry for Nutrient Testing?
Nutrient testing provides you with important information about what nutrient levels need adjusting and how much you need to adjust. It can also analyze the texture of your soil and determine how you can improve it.
Nutrient and pH levels are measured most accurately in a professional laboratory. Local governments and universities often offer these tests on soil samples you collect. Additionally, there are basic pH and nutrient testing kits you can use on your own, though they are not as precise as laboratory data.
Reusable meters are also available for pH testing.
If you send your soil to a professional laboratory for analysis, they will often provide specific recommendations for your soil. Be sure to provide them with as much information as possible, including what you plan to plant in the area, to get the most out of your personalized feedback.
Ultimately, you need to identify the specific problems in your soil before adding soil conditioner to ensure you do not over-supplement the soil.
Using Soil Conditioner in Your Garden
Soil conditioner can greatly contribute to your garden if you use it sparingly.
You can combine soil conditioner with your soil or place some above it. When you put the soil conditioner on top of the soil, the nutrients will slowly make their way down to the roots with the water. However, it is more susceptible to erosion and runoff.
If your garden is on a slope or in an area prone to pooling during heavy rainfall, mixing the conditioner with the soil is the best way to ensure the conditioner is accessible to the plants.
Plants absorb nutrients through their roots, so the root depth of your plants will determine how far down the conditioner needs to be added. Root vegetables such as carrots and onions grow very shallowly, so you only need to add conditioner to the top few inches of soil.
After identifying the adjustments that need to be made to your soil, make these changes gradually. Be careful not to over-correct by adding too much soil conditioner. You also need to test the soil regularly.
It’s recommended that you test soil quality every few years, but when making changes, you must test more often, such as every 1-2 months.
Tips for Using Soil Conditioner
It is very important when using soil conditioner that you don’t use too much, but you also want to use enough to actually have an impact on the soil. There are quite a few other things apart from this to also be aware of.
When using soil conditioner follow these tips:
- Till up about 3 or 4 inches (7.62-10.16 cm) of soil either in the ground or in your pot and mix your soil conditioner with it. It is recommended that you do this before you plant your vegetation in order to help in disturbing the plant less.
- Be sure after using soil conditioner to check for feeds or other unwanted vegetation that might be preventing your plant from growing. Since the soil conditioner is so rich, other plants that might not have succeeded previously are more likely to grow. If you see weeds or other plants start to sprout, remove them immediately.
- If it doesn’t look like your soil conditioner is working, try giving it a little bit more time. While soil conditioner instantly puts the important nutrients into the soil, it sometimes takes a moment in order for the plants to actually absorb the nutrients. Wait three weeks before reapplying more soil conditioner.
- Reapply if your soil eventually lacks nutrients once more. Generally, one round of soil conditioner is enough to last for a full season, but you might need to reapply the soil conditioner in following years. Additionally, if it is an especially wet year, you might need to use a soil conditioner more than once.
Final Thoughts
While soil conditioner is great for improving soil quality, it can not be used as a replacement for potting soil. Soil conditioner is too thin and too full of nutrients to be able to sustain plant life by itself, but it can be used as an additive to both potting and garden soil to improve soil structure and nutrients.
When using soil conditioner, be sure not to use too much. One application of soil conditioner in a season should be sufficient, but you may need more than one application depending on the soil depletion over the year.
If you consider using soil conditioner for your garden, you could read my other article here: Is Soil Conditioner Worth It? How to Decide
