When comparing the ingredients of potting soil and fertilizer, you will find that many of them are the same. Indeed, these common gardening components share many similarities, so it is hard to tell the difference between them. You may even wonder if potting soil and fertilizer are the same and go by two different names.
Potting soil is not the same as fertilizer, and you can’t use the two products interchangeably. Potting soil is a growing medium, whereas fertilizer is an amendment. While potting soil has some essential nutrients for proper plant growth, gardeners usually add fertilizer as an enhancement.
In this post, I’ll explain what potting soil and fertilizer are, what you may use each product for, and how to use them together. I’ll also answer some commonly asked questions and share my recommendations for the best potting soils enhanced with fertilizers.
Potting Soil vs. Fertilizer: Understanding the Differences
Let’s look at potting soil and fertilizer and how they are used to understand the difference better:
Potting Soil
Potting soil is a growing medium typically used in containerized gardening. It contains various ingredients such as peat moss, perlite, vermiculite, and others beneficial to plant growth. One component often lacking in potting soil is actual soil since it is too heavy for houseplants.
Although it is called soil, most potting soils are a soilless mixture.
In addition to those noted above, some common ingredients of potting soil include:
- Bark
- Clay
- Coco coir (coconut coir/coco moss)
- Compost
- Humus
- Limestone
- Permite
- Sand
- Silt
- Sphagnum moss
While many of these components may supply some critical nutrients that plants need, the amount is too low to be advantageous for some plants. Thus, gardeners usually add fertilizer to help enhance certain elements.
If you are interested in learning more about improving your soil quality, check out this article: How to Improve Soil Quality (The Ultimate Guide)
Types and Purpose
As the name suggests, manufacturers market potting soil for use with potted plants and containerized gardening. They create different mixtures with specific plant needs in mind, and you can find specialized potting soil for any variety of plants you wish to grow.
Some of the more commonly used types of potting soil are:
Indoor
Indoor potting soil suits houseplants and contains ingredients that promote nutrient retention and proper drainage. These also typically avoid using bark and other components that may harbor common pests.
Outdoor
Manufacturers design outdoor potting soil specifically for potted plants living outdoors. It contains water-retaining materials such as peat moss or even topsoil. This soil also usually has fertilizer and other organic materials added for nutrition.
Compared to indoor soils, outdoor potting soils are heavier to better withstand environmental elements such as rain and wind.
All-Purpose
Suitable for any potted plant, all-purpose soil offers the benefits of indoor and outdoor soil in one. These soils contain various ingredients that encourage good aeration, drainage, and moisture retention. They also have a fluffier texture similar to indoor soil yet are a bit heavier, like outdoor potting soil.
Raised Beds
Purposed for outdoor garden beds and ideal for growing fruit and vegetable plants, raised bed potting soil uses larger materials to create better aeration and drainage. These are also packed with nutrition and use slow-release fertilizers to replenish nutrients throughout all development stages.
Fertilizer
Fertilizer is a source of nutrients for plants added to enhance soil and other growing mediums. It may be organic or synthetic and is used to supply nitrogen, phosphorus, and potassium (NPK), the essential nutrients plants need for healthy development and growth.
Primarily, fertilizers provide these three essentials.
Shortened in the green thumb community as NPK, these macronutrients work together to ensure proper plant growth and overall health:
- N (Nitrogen): Required for photosynthesis and chlorophyll creation
- P (Phosphorus): Essential for cell division, protein synthesis, and other complex processes
- K (Potassium): Needed to ensure robust, healthy plants that can endure their environment
Additional Nutrients
Yet, every plant has unique nutritional needs, and fertilizers can help to provide some other specific nutrients that potting soils may lack.
Some common nutrients supplemented with fertilizers include:
- Calcium
- Chloride
- Iron
- Manganese
- Sulfur
- Zinc
Types of Fertilizer
You may categorize fertilizers by their ingredients and physical form or application process.
When it comes to ingredients, fertilizers are either organic or synthetic. Organic fertilizers are natural materials such as manure or compost, whereas synthetic fertilizers contain chemicals.
In addition, fertilizers can be either wet or dry.
You may easily spray liquid-soluble fertilizers on top of plants and soils for a rapid nutrient boost. They can be applied as often as once a week. On the other hand, dry fertilizers are spread over an area near the root zone before planting and alongside plants as needed.
Composition and Nutritional Content
Some potting soil mixes contain fertilizer, yet most organic and soilless options do not. Many potting soils have slow-release fertilizers or other conditioners added to them for additional nutrition, which the manufacturer will clearly label on the packaging.
If you want potting soil with fertilizer added, keep an eye out for products marketed as a potting mix. These products are potting soil enhanced with fertilizers or other amendments. Some premium brands even include organic topsoils as conditioners.
Remember that while combination substrate and fertilizer potting mixes are convenient, manufacturers design them for specific plants. Indeed, this can be useful if you are growing only a few types of plants with similar nutritional needs.
However, if you have a variety of plants with different growing requirements, potting soil without fertilizer gives you the control to add nutrients at your discretion.
You’ll need to add fertilizer to some potting soil mixes to enhance them. Unless specially formulated for a plant type, potting soil usually lacks some of the extra nutrients needed for proper plant growth. Even NPK potting mixes may require additional fertilizer to supply other necessary nutrients.
Conclusion
Potting soil and fertilizer are not the same, and each has a different purpose. Yet, both play an essential part in plant development and growth. More often than not, you will need to add fertilizer to your potting soil to provide optimal nutrition and conditions for your plants.
To learn more about the differences between fertilizer and potting soil, you can check out this article: Fertilizer vs. Potting Soil: The Differences Explained
