I found that potting soil is a must when growing plants in containers. But what does it contain and does this include fertilizer? I tried to find this out and I’m writing this post with my research.
Potting soil does not contain fertilizer because it’s not actually soil but sterile media. However, you now get potting soil that come with added fertilizer. You should check the package for the ingredients if fertilizer is included in the potting soil.
The potting soil you buy will determine how good your plants will grow. You may need to add fertilizer yourself if it does not already contain some. I’ve added some information below on the fertilizer you can add to the potting soil and how you can do it with ease.
What are the ingredients of potting soil?
The potting soil you buy does not actually contain soil. That’s why it’s also known as a soil-less mix or a potting mix.
The ingredients of the “traditional” potting soil are supposed to only help provide the right texture to it. This texture helps the soil retain enough moisture for the plant’s roots while draining out the excess.
This texture will allow good air circulation among the plant’s roots that help it absorb nutrients from the soil.
The most common ingredients you will find in potting soil are peat moss, perlite, and vermiculite. Peat moss is an organic material obtained from the peat bogs located in certain parts of the world like the US and Canada.
The peat moss provides the potting soil its moisture-retaining capacity because it’s good at absorbing moisture and releasing it slowly. The problem with peat moss is it’s an expensive material.
There is only a limited supply available in the entire world which increases the cost and makes it unsustainable. A cheaper and sustainable alternative to peat moss is coco peat.
The remaining two ingredients you usually find in potting soil are perlite and vermiculite. These are materials processed from volcanic rock.
The purpose of these two is to provide a light and airy texture to the potting soil. This helps improve the air circulation among the plant’s roots. Vermiculite does have water-retention properties like peat moss.
You can make your own potting soil if you mix these three ingredients in the right ratio. You need to use 2 parts peat moss or coco peat, 1 part perlite, and 1 part vermiculite.
Do you need to add fertilizer to potting soil?
We now know what the ingredients of a traditional potting soil are. And as you can see there is no fertilizer added to such soil.
When shopping for potting soil, you need to check the bag for the ingredients. If the potting soil already contains fertilizer, you don’t need to add it yourself at first. You will need to add fertilizer later once the fertilizer in the potting soil has been exhausted.
Also, there are some plants like cilantro that would do just fine without adding any fertilizer. But there are several plants that will need a supply of nutrients when grown in a container.
When plants are grown in garden soil, the roots can reach into the ground and extract nutrients that are present. But when growing a plant in a container with potting soil, the roots cannot find such nutrients.
That’s why it’s a good idea to add fertilizer to the potting soil so your plants get the best chance of growing healthy.
Another option you have is to add compost to your potting soil when preparing the container with potting soil. The organic compost contains nutrients and microorganisms that are beneficial to your plants.
If you do have compost available, I would recommend adding that to the potting soil instead of any fertilizer.
If you don’t have compost, you can add organic or synthetic fertilizer to your potting soil. While both kinds of fertilizer will work for your plant, I always recommend going for organic.
The benefit of using organic fertilizer is it’s sustainable, does not harm beneficial organisms in the soil, and will not burn the plants as easily.
As a beginner, I would suggest using a readymade organic fertilizer instead of trying to mix up your own.
Once you have some experience growing plants, you will be able to make your own fertilizer mix that would be based on the specific needs of the plant.
Here’s a list of potting soil you may find useful.
- Fox Farm Happy Frog Organic Potting Mix
- Burpee Natural Organic Premium Growing Mix
- Black Gold All Purpose Potting Soil
- Perfect Plants Organic Potting Mix
- Espoma Organic Potting Mix
How do you add fertilizer to the potting soil?
You need to be careful when adding fertilizer to the potting soil. You don’t want to add too little where your plants don’t get the benefit. And you don’t want to add too much and risk burning your plants.
I would suggest to carefully follow the instructions you’ll find on the fertilizer bag or container. This will give you the most out of using the fertilizer
You can get two different types of fertilizer for your potting soil. It could be a slow-release granular fertilizer or a liquid fertilizer.
Slow-release granular fertilizer
The slow-release granular fertilizer will be released into the potting soil every time you water it. The benefit of using such fertilizer is you just need to add it 2-4 times to the potting soil.
The first time you can add it is when you are preparing the container with the potting soil. Just mix in the required amount of slow-release fertilizer.
As a general rule, you want to mix 1 tablespoon of a slow-release fertilizer per gallon of the potting soil.
This application will last you about a month and then you can apply another batch. You just need to apply the slow-release fertilizer 1-2 times during the growing season.
Here is a list of slow-release organic fertilizer you can use.
- Dr. Earth Organic Fertilizer
- Burpee Natural Organic Fertilizer
- Espoma Plant Tone Fertilizer
- Tomato-tone Organic Fertilizer
A liquid fertilizer is something that you dilute with water before using on the potting soil. Follow the instructions on the container on how much to use.
As a general idea, you can use 1 ounce of liquid fertilizer per gallon of potting soil.
You can use liquid fertilizer once every two weeks during the growing season. You could also use the liquid fertilizer every couple of days as long as you dilute it even further.
Add 1 part of the fertilizer to 5 parts water to dilute it enough that you can use almost every day on your plants.
The benefit of using liquid fertilizer is you can spray it on the potting soil as well as directly on the leaves. So the plants can absorb the nutrients fast.
You can also apply the liquid fertilizer as part of your watering schedule where you just add the fertilizer to a can of water.
Here is a list of organic liquid fertilizer you can use.
- Neptune’s Harvest Organic Fertilizer
- FoxFarm Grow Big Liquid Fertilizer
- Espoma Organic Grow Fertilizer
- Great Big Tomatoes Fertilizer
How long does fertilizer last in potting soil?
The amount of time fertilizer will last in the potting soil depends on the type of fertilizer and how much you’re using.
I recommend always using the amount that is specified by the manufacturer on the fertilizer bag or container.
Once a slow-release fertilizer has been added to the potting soil, it will last about a month before you need to reapply. Every time you water the potting soil, some of the fertilizer will be released into the soil and become available to the roots.
A liquid fertilizer that is applied to the foliage is immediately available to the plant for use. But if you spray it in the soil, the liquid fertilizer will be absorbed into the soil and stay there for a couple of weeks.