Fertilizer and potting soil are both commonly used gardening add-ins that play essential roles in plant growth and development. However, they are not interchangeable and perform different functions.
Fertilizers can be organic or inorganic and are added to the growing medium to feed plants with the macro and micronutrients they need. On the other hand, potting soil refers to the substance used to grow plants, and while it may contain some nutrients, it typically needs additional fertilizer.
In this article, I’ll examine whether fertilizer and potting soil are the same. I’ll also explore what fertilizer and potting soil are in more detail so you can better understand how they should be used. Finally, I’ll delve into the relationship between soil and fertilizer, so read on to learn more!
Are Soil and Fertilizer the Same Thing?
Soil and fertilizer are both necessary for plant growth and survival, but they are not the same and don’t serve the same purpose. The main difference between soil and fertilizer is that they support the plant growth process in different ways.
Soil and fertilizer are not the same thing. Soil is a substrate used to root plants in while offering structural support to them. It may contain some nutrients. Fertilizer is a substance that may be organic or inorganic and used to supply plants with all the nutrients they need to thrive.
Apart from the differences in function, soil and fertilizer are also made up of different elements. Soil comprises organic and inorganic matter, liquids, gasses, and organisms. As a result, plants can get most of the nutrients they need from the soil.
However, plant nutrients can be divided into macro and micronutrients on the basis of how much plants need them. Plant macronutrients, as the name suggests, are nutrients that plants need in large quantities, which include:
- Nitrogen
- Phosphorus
- Potassium
These macronutrients are quickly depleted in the soil, regardless of the soil type. Organic or inorganic amendments need to be added to the soil to replenish these nutrients, and these amendments are known as fertilizers.
Pesticides are also amenders, but they are different from fertilizers and used to prevent pest attacks.
Fertilizers are made up of the macro and micronutrients needed by plants, fillers, and carriers like sand, which are used to round out the fertilizers and make them spreadable. Different fertilizers are available depending on the application, the rate of release, and whether the materials are organic or not.
When choosing a fertilizer, you’ll need to assess your plants’ requirements first.
The next step would be to get a soil analysis done because fertilizer is used to amend the soil with the necessary nutrients. Adding more fertilizer than necessary can lead to fertilizer burn, which significantly delays play growth and yield as the plant recovers.
Unfortunately, plants cannot grow with fertilizer alone. Fertilizer is a chemical substance that you add to a plant’s soil as a helpful addition. There are two main types of fertilizer: organic and synthetic.
Organic Fertilizer
Organic fertilizer is the safer fertilizer to use, but it takes time to kick into action. Gardeners must plan accordingly and measure out the correct amounts for this style of fertilization.
Many choose to make homemade organic options, but there are also some great store-bought fertilizers on the market today. Here are a few examples of organic fertilizer:
- Seaweed fertilizer
- Manure
- Compost
- Fish Emulsion
- Bone Meal
Synthetic Fertilizer
Synthetic fertilizers, on the other hand, are chemical-based fertilizers that quickly release nutrients to plants for easy access. Many choose this option because it is the most popular and provides rapid results.
However, synthetic fertilizer can lead to fertilizer burn relatively fast if you are not careful and it can have unfavorable long-term effects.
Synthetic formulas also contain minimal ingredients, so many people love this option. It provides what plants need on a chemical level and nothing more.
Synthetic fertilizers come in a few different varieties:
- Dry formula
- Pellets
- Liquid formulas
Individuals can also apply their fertilizers in a few other ways, which can apply to both organic and synthetic formulas:
- Time-sensitive release
- Foliar
- Side-dressing
- Soil application
The Relationship Between Soil and Fertilizer
Soil and fertilizer are both important for plants. Garden soil may contain some or all of the nutrients that plants need, but potting soil doesn’t until you add fertilizers into the mix.
Fertilizer is essential, as it provides all the nutrients necessary for your plants to grow and thrive; however, these nutrients can only be fed to plants through the soil. Fertilizers are soil amendments. As plants absorb nutrients through their roots, fertilizers are added to the soil.
While liquid fertilizer can be sprayed to the surface of leaves, the process is expensive and not a substitute for plants uptaking nutrients through their roots.
However, to improve overall soil quality, you must incorporate more organic matter into the soil.
The best approach is to use organic fertilizers like compost or slow-release fertilizers like spikes. These fertilizers improve microbial activity in the soil and release nutrients slowly, in manageable quantities for plants to use.
How Do I Know if My Soil Needs Fertilizer?
Most plants need regular fertilizer applications, especially during the growing season when they draw on the nutrients in the soil to grow as much as possible.
The best way to know if the soil needs fertilizer is to conduct a soil analysis, which will tell you what nutrients your soil needs so you can fertilize accordingly. Another way to tell that your soil needs fertilizer is if your plants start showing signs of nutrient deficiency.
A soil analysis is a good practice to implement for garden soil. When it comes to potting soil, the only source of nutrition is fertilizer. So if you hadn’t added any when you first potted your plants, you’ll need to fertilize your plants sooner rather than later.
Understanding Soil
Soil is a substance made up of organic and inorganic matter, minerals, nutrients, moisture, air, and several organisms, and is indirectly the source of all life on earth as plants are grown in soil. Herbivores and omnivores feed on the plants, and omnivores feed on herbivores.
Soil is vital when it comes to plant growth for many reasons, and understanding soil, its types, components, and functions will help us distinguish it from fertilizers.
Types of Soil
There are many different types of soil, each with its advantages and disadvantages. When referring to the soil types, we’re talking about the texture of soil and how that affects water and nutrition retention.
Soil texture is determined by the relative proportions of sand, silt, and clay within the soil. Based on the proportions, the soil may be categorized into:
- Sandy: Sandy soils are typically made up of up to 70% sand, which has the largest particles among sand, clay, and silt. This allows for great drainage in sandy soil but poor water and nutrition retention. For this reason, topsoil with more than 70% soil is not recommended for plant growth.
- Clayey: Clay has the finest particles among the different soil types, making it great for water retention. However, the size of the particles means that the compaction is also high, which can lead to a limitation in the amount of air present in clayey soils.
- Loam: Loamy soils are ideal for gardening because they have a balanced sand, silt, and clay ratio. Silt has particles sized in between clay and sand, and when combined in the right ratio, the soil becomes a well-draining mix that can also hold on to sufficient nutrition.
The ability of soil to hold onto water and nutrition is important for plant growth. Sandy soils are hard to grow plants in, even with the addition of fertilizers, because the fertilizers will be leached away.
Components of Soil
Soil provides nutrition to plants, but nutrients are only part of the components found in soil. Some of the functions of soil include:
- Medium to grow plants,
- Water filtration,
- Breakdown and recycling of organic materials,
- Habitat for several single and multi-celled organisms, and
- Materials for construction activities.
Soil can only perform these myriads of functions because of its many components. Here are some of the most important components of soil.
- Minerals: The minerals present in soil comprise about 45% of the soil. These minerals are stable elements and compounds that supply nutrition to plants. Minerals may supply both macro and micronutrients but are typically a great source of micronutrients for plants.
- Organic matter: Organic matter supplies nutrition to the organisms living in the soil, which breaks the matter down to humus. This breakdown releases macronutrients like nitrogen into the soil, which plants can uptake and use to grow and live.
- Air: Like all organisms, the inhabitants of soil also need air. Compacted soils like clay have less air than loamy soils, which means they have fewer organisms living in them. As a result, they won’t be as rich in humus and nutrition from the breakdown of organic matter.
- Water: Water is essential for life, and depending on the size of the particles, a type of soil may have different capacities for water retention. Soils like clay hold on to too much water, which is as bad as sandy soils that can’t hold on to any water at all. Plants either drown or suffocate in these soils.
- Living organisms: The living organisms in the soil are the ones who perform the process of breaking down and recycling the organic matter. These living organisms are essential for soil health, and soils that are more bioactive tend to be healthier than soils that are not.
Importance of Soil for Growing Plants
Soil is a medium for plants to grow, which means that soil and all its components are the material in which plants grow their roots. Plants anchor themselves to the ground through the soil, and the soil keeps them upright, allowing them to grow upwards towards the light.
Like all living organisms, plants also need air and water, which they uptake from the soil. Along with water, plants uptake nutrients from the minerals and organic matter present in the soil, which they convert to energy through photosynthesis.
Nutrients are only a part of what plants receive from the soil, and in areas where the plant density is heavy, these macronutrients deplete very quickly. Nutrient depletion is especially prevalent in garden soil, agricultural land, and pots.
In garden soil and agricultural land, plants and crops must produce high yields in short amounts of time, which uses an extensive percentage of nutrients and water supply.
What Is Potting Soil?
People worldwide rave about soil and fertilizer in the gardening world, and there’s an excellent reason for it. However, potting soil is also a great option that gardeners shouldn’t dismiss, as it can help plants thrive in many different ways.
Potting soil is an alternative planting mixture that contains ingredients to mimic soil. Usually, potting mixtures do not have soil and are used for potted plants only. Gardeners can use it to help their plants thrive in a container because, sometimes, soil can bunch up, preventing healthy roots.
Many avoid using potting mixtures because it does not contain any soil. However, potting mixes are excellent additions for gardeners who care for potted plants.
Soil, unfortunately, sometimes carries pathogens and fungi that can harm plants. Plants rooted in the ground can handle pathogens and fungus, but plants in a pot are sensitive and need room for drainage and root growth.
As great as ground soil is, it can cause more significant issues if used in a pot. Potting mixes contain the following:
- Bark
- Perlite
- Vermiculite
- Sphagnum moss
- Other ingredients like compost
Any organic material like compost in a potting mix will feed your plant, while the other ingredients help with drainage and moisture.
All in all, potting mix is a safe alternative for potting plants. Using potting mixture on the ground or even in garden beds is not recommended because of the cost and usage.
If you want to learn more, you can read my more elaborate article on the differences between fertilizer and potting soil here: Fertilizer vs. Potting Soil: The Differences Explained
Garden Soil vs. Potting Soil
Garden and potting soil are both mediums for plant growth, but they are not the same thing. As the name suggests, garden soil refers to the soil present on the ground in your gardens, which is probably made up of the components of soil discussed earlier in this article.
On the other hand, potting soil often has very little actual soil in it. It is a medium made up of different components that might include peat, bark, sand, vermiculite, and coco coir, among others.
These components are usually sterilized to prevent weed growth and pathogens.
Potting soil mixes can vary depending on the type of plant they’re used for. They tend to have adequate drainage, as well as sufficient water and nutrition retention properties.
However, there are no organisms performing the function of organic material recycling in potting mixes. Potting mixes also don’t have any minerals other than those found in their materials.
Potted plants need to be fertilized more often than plants growing in the ground as the increased drainage tends to leach the nutrition in the mix away. Organic fertilizers like compost and manure are often mixed in with potting soil to provide nutrition and improve water retention.
Do Potting Mixes Contain Soil?
Potting mixes have specific ingredients in their mix, and there is an excellent reason for it. Potted plants require proper drainage and nutrients, which cannot always be given through traditional soil, even if it is added to a potting mix.
Most potting mixes do not contain soil because soil can harm the plant’s rooting system. Soil has fungus and pathogens that can potentially weaken a plant’s roots, preventing it from growing.
Some potting mixes contain a little bit of soil, but it is uncommon. People may refer to these mixtures as potting soil rather than potting mix. If there are any additives in potting mixes, individuals may find compost or other organic ingredients.
The potting mix gives plants the nutrients they need and has great water retention. It’s light and fluffy, so plants can breathe and grow properly without the risk of suffocation.
Guide to Fertilizers
While soil can provide plants with nutrients, these nutrients deplete quickly as plants grow and need to be replenished.
Fertilizers provide the macro and micronutrients that plants need to survive and grow. Among these, macros are used up much quicker, so most fertilizers aim to add nitrogen, phosphorus, and potassium to the soil. The ratios of these nutrients are typically labeled as NPK on the fertilizer packets.
There are different ways to categorize fertilizers (each of these varieties of fertilizers can be used to meet different needs in plants).
Types of Fertilizers and How They’re Used for Plants
Based on their composition, fertilizers can be categorized into:
- Organic: Organic fertilizers are materials like compost or manure that occur through natural processes like excretion or decay. These tend to be nitrogen-heavy and not only provide nutrition to plants they also improve soil quality and bioactivity in the soil. Other organic fertilizers include fishmeal, blood meal, and bone meal.
- Inorganic: Inorganic fertilizers are synthetically created and composed of mineral salts that offer nutrition to plants. They can be applied in a number of ways and tend to work very quickly unless they’re specially treated. These come in any ratio of NPK and can be mixed together.
Based on their application, fertilizers can be divided into the following:
- Granular: Most granular fertilizers are inorganic fertilizers. They can be worked into the soil or broadcast on the surface depending on the season. Granular fertilizers are the most commonly used fertilizers in gardens as they’re easy to use and mess-free.
- Liquid: Liquid fertilizers can be organic, like compost tea or inorganic. Liquid fertilizers are useful due to their versatility, as they can be easily diluted. They can be applied to the roots and to the leaves in a foliar application of nutrients.
- Fertilizer Spikes: Fertilizer spikes are expensive but convenient to use and preferred for their longevity. In a pinch, you can break these fertilizer spikes before use or even dilute them in water and apply them for a quick nutrient supply.
Based on how they release nutrients, fertilizers be classified into:
- Slow-release: Slow-release fertilizers are not water-soluble. Instead, the nutrients are released through changes in soil temperature, pH, and microbial activity. This makes nutrients available to plants in easily usable quantities when the plants need them
- Fast-release: Fast-release or quick-release fertilizers are always inorganic fertilizers that make nutrients immediately available to plants. Among these, liquid fertilizers work the fastest, and diluted solutions are often used for seedlings as a starter fertilizer.
Can I Use Fertilizer Instead of Soil?
You can’t use fertilizer instead of soil because soil provides a medium for plants to root in, unlike fertilizer. The structure, minerals, and water retention capacities of soil cannot be mimicked by fertilizer. Additionally, too much fertilizer can stunt plant growth and cause fertilizer burn.
Growing plants without fertilizer is always possible; therefore, fertilizer can never replace soil. Soil provides structure, support, air, and water to plants, without which they cannot live or grow. Most soils contain at least some amount of the macronutrients that plants need.
Plants cannot be grown in fertilizer because adding too much fertilizer to plants has a number of detrimental effects on them. The plants will grow too quickly, become susceptible to disease and pests, and reduce yields.
Fertilizer burn is a likely effect of growing plants in inorganic fertilizers, as these contain mineral salts. The salts will draw water out of plant tissue, leading to dehydration and, eventually, plant death.
Do I Need Fertilizer if I Am Using a Potting Mix?
Potting mix is an alternative to soil, which contains certain ingredients that are very different from the soil. Due to this, many may wonder if they can use fertilizer in a potting mix.
You need fertilizer for your plants if you’re using a potting mix, regardless of which soil or potting mix you use. All plants need the three main ingredients of nitrogen, phosphorus, and potassium in their soil or plant mix to thrive and grow successfully.
Potting mix has excellent ingredients that help plants flourish in a potted container. However, there are certain macronutrients and micronutrients that plants and soil need to grow big and strong:
- Nitrogen helps plants grow strong leaves with a green color.
- Phosphorus helps plants produce successfully and establish strong roots.
- Potassium helps with the overall growth of a plant.
Without these main ingredients, plants can still grow, although not as optimally. If you’re considering growing your plants without fertilizer, it is recommended to add additives, at the very least.
Gardeners should try to use organic fertilizers if they can. Compact soil and chemicals can be harsh on a plant that is in a container, and since these plants are already relatively sensitive, natural substances can help them thrive.
Best Organic Fertilizers for Potting Mix
The gardening market has many great fertilizers available, which can help plants. Organic options, however, are recommended for plants that are potted or in a container.
Potted plants have obstacles since they grow in small spaces. Synthetic fertilizers can be helpful in small doses or diluted dosages, but potted plants are at higher risk for fertilizer burn.
Conclusion
Fertilizer and potting soil are both essential for plant growth, but they are not interchangeable. While fertilizer is used to feed plants the nutrients they need, potting soil (and other types of soil) provide a medium for the plants to grow and anchor themselves.
Fertilizer needs to be added to potting soil to feed the plants because, unlike gardening soil, potting mix has no minerals or organic matter to supply the necessary nutrients to the plants.
To learn more about fertilizing indoor and outdoor plants, you can check out this article: How to Fertilize Indoor & Outdoor Plants (Ultimate Guide)
