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Learn how to make your own DIY potting soil mix for your seedlings! This is a great recipe to mix at home to get a head start on your gardening season.

Why should I make my own potting mix
You may be wondering why you shouldn’t just buy some potting soil from the store to use for your seedlings. While it is totally fine to buy your own potting mix making your own can save you money.
Another benefit of making your own potting soil is you know what is going into the mix.

Making your own potting mix can help you grow the best seedlings ever! I have been able to grow my best plants by using this potting soil recipe.
Potting soil ingredients
Contrary to popular belief, you should not just use garden soil or top soil for your seedling mix. This soil can have unwanted fungal diseases, weed seeds, and pests that will harm your plants.
Using garden soil or topsoil can lead to a seedling problem called damping off where the seedlings die. If you want healthy seedlings, don’t use topsoil.
A good seed starting mix actually doesn’t have garden soil in it! This mix has ingredients that help young seedlings grow well without needing topsoil.
There are 5 main ingredients for this potting mix recipe. Below I will explain what each item is, where you can buy it, and why it is included in this recipe.
- Coconut Coir
- Worm Castings
- Perlite
- Vermiculite
- Trifecta+ (fertilizer)
Coconut Coir
Coconut coir is the husk of coconuts that is ground up to be used in gardens. This coir is a byproduct of the coconut industry, but gardeners have found a use for it.

What does it do
Coconut coir adds water retention qualities to your soil mix, so it will not dry up quickly. It is also light and fluffy creating air pockets in the soil.
Coconut coir is a newer item in soil mixes, because they used to use sphagnum peat moss in soil mixes. Peat moss does not hold as much water as coconut coir and I find that it can become hydrophobic if it dries out.
There are also concerns as to how sphagnum peat moss is being harvested, so some gardeners have abandoned it completely.
Substitutes
Coconut coir can be substituted for equal parts of sphagnum peat moss. If you do add peat moss instead of coconut coir, you will have to add in agricultural lime to correct the PH. You only have to add the lime to the soil if you decide to use peat moss.
Where to buy coconut coir
When buying coconut coir you need to look for coconut coir that has low salt content. Salt can be in coconut coir and that can affect your plant’s growth.
You can buy the same type of coconut coir that I bought here that is buffered and has low salt content.
Worm castings
Worm castings are quite literally worm manure! These castings are created when worms eat food waste and turn it into manure.

What does it do
Worm castings are rich in the nutrients that plants need to grow. This recipe has worm castings to improve plant growth as coconut coir does not have many nutrients in it.
An added benefit is that worm castings are also full of bacteria and soil life that promotes plant health. These castings help add in the good bacteria while keeping out the fungal diseases.
Substitutes
Compost can be substituted for worm castings with the same ratio. Please be mindful that compost that has not been heated correctly may contain weed seeds. Compost can add in unwanted soil bacteria, so to be on the safe side opt for worm castings.
Top soil is another substitute for worm castings in this recipe following the same ratios. I really don’t recommend this substitute, because it can contain weed seeds and it does not offer as many nutrients to your plants.
Where to buy worm castings
You can find worm castings at many garden stores and retailers. You can find the same worm castings that I used here.
If you make your own worm farm you can save money on worm castings and use your own!
Perlite
Perlite is white in color and looks similar to ground up Styrofoam. Perlite is not Styrofoam, but is volcanic glass that has been “popped” like popcorn.

What Does It Do
Perlite keeps soil airy and allows for good drainage in potting mix. Perlite is a necessary part of soil mixes to keep them light and fluffy.
Make sure to add perlite to your growing medium. This recipe is great for most vegetable seedlings. However, if you find that your soil will not drain, add perlite; if it is draining too fast, you added too much perlite.
Substitutes
Biochar is a great substitute for perlite and has many added benefits. You can learn how to make your own biochar here.
Another alternative to perlite is rice hulls. Rice hulls should offer the same aspects that perlite does; although, I have not used them before.
Where to buy perlite
I thought that I could just buy any type of perlite, but soon found that to be wrong. Some companies will add fertilizer to their perlite to “enrich” it. If the perlite is not certified organic, then the fertilizer is most likely synthetic.
I found this perlite that is organic and does not contain any synthetic fertilizers. I really like the quality of this product!
Vermiculite
Vermiculite is a mineral that is heated to expand it. Vermiculite is similar to perlite, but it does serve a different purpose.

What does it do
Vermiculite has many pores in it that hold onto moisture and nutrients in your soil mix. This vermiculite helps to retain the soil’s natural nutrients and holds water close to the plant’s roots.
Store-bought soil mixes have about 5% vermiculite in them. When you make your own mix you can add more vermiculite to help your seedlings get off to a great start. It is optimal to have about 10-15% of the soil mix vermiculite. My mix hits this range right in the middle.
While some think that perlite has the same qualities of vermiculite that is wrong. Vermiculite is said to hold much more water than perlite does.
Substitutes
Biochar is the only substitute for your own seed-starting mix. Biochar has the same porous qualities and can hold onto the water and nutrients. If you are also using biochar in place of perlite, add the same ratio for vermiculite.
Where to buy it
Non-organic vermiculite can also have additives that you don’t want in your soil medium. I found this organic vermiculite for my mix. If you shop at your local garden center just confirm that the vermiculite is organic.
Trifecta+
Trifecta+ is a fertilizer that is made by a small seed company called MIgardener located in Michigan. This company offers heirloom seeds and is noted for making Trifecta+ fertilizer.

What does it do
Trifecta+ is a fertilizer that can be used on all types of plants. To make the best potting soil, I added this into my mix.
This fertilizer offers many nutrients that your plants need. While this product is not certified organic, I believe that the ingredients are fine to add to my soil.
None of Trifecta+ ingredients are made from synthetic chemicals, but it is too time consuming and expensive to get their fertilizer certified organic. MIgardener does offer a complete list of the ingredients that they use to make Trifecta+.
Substitutes
If you want the best seedlings, I recommend that you use Trifecta+ in your seedling mix. This fertilizer offers both fast and slow release nutrients so that you don’t need to water your plants or fertilize often.
If you choose not to add Trifecta+ you can add other organic fertilizers; just make sure to follow the packages instructions.
Where to buy Trifecta+
Even though Trifecta+ is made by a small company you can buy it through Amazon. MIgardener offers this fertilizer in three different sizes. For this seedling mix you will only need 3 tablespoons per gallon of soil.
Best Seed Starting Soil Recipe!
Now that you know all the ingredients needed here is the recipe for the best seed starting mix!
2 parts coconut coir
1 part worm castings
1/2 part perlite
1/2 part vermiculite
3 Tablespoons Trifecta+ per gallon of mixed soil
A part can be anything you choose! I used the empty worm casting bag to measure out the perfect amount of ingredients I needed.
To find the gallons of soil that you have mixed, simply measure the height, width, and depth of your soil and multiply those numbers to find the cubic feet.
Every cubic foot of soil is about 7.5 gallons of soil. So add three tablespoons of Trifecta+ for each gallon of soil you have.
How to mix this soil recipe
Here is how I mixed this soil recipe. You might find these items handy when mixing your seed-starting mixes.
- Large Tote
- Trowel or hand rake
- Gloves
Step 1
When you buy coconut coir it comes in bricks that are called coco coir bricks. These bricks of coconut fiber will need to be hydrated before they can be used.
To hydrate your coco coir bricks you simply pour warm water on the brick and it expands to about 6-7 times it’s original size. Make sure to check the packaging to see how much water you should add.

I hydrated the coco coir brick first so I could use the same tote to mix my soil. After hydrating the coco coir, I placed it back in the bags that came with the coconut coir I bought.

Step 2
Now that you have your tote cleaned out after hydrating the coco coir you can start to mix your soil. Add in one part of worm castings to your tote. If you used the entire bag of worm castings, you can use this as your part for the rest of the recipe.

Step 3
Add in two parts of your hydrated coconut coir.
Step 4
Add in one half part perlite and one half part vermiculite to the tote. If you substituted biochar for both the perlite and vermiculite, then just add in one part biochar.
Step 5
Mix all your ingredients well! You can just use your hands or you can use a garden trowel or rake for this job. Next time I will make sure to use a hand rake because my hands were coated in soil.

Step 6
After you have mixed the soil thoroughly, calculate the cubic feet of your soil and convert it to gallons. Then add in 3 tablespoons of Trifecta+ for each gallon of soil and mix that in well.
You now have the best soil mix for starting seeds. This soil mix is great for delicate seedlings to grow in, and my own seedlings did great! Now you can use this soil for your seeds!

Best DIY Potting Soil Mix
An organic soil mix that will grow the best seedlings you have ever seen!
Ingredients
- 2 part coconut coir
- 1 part worm castings
- 1/2 part perlite
- 1/2 part vermiculite
- 3 Tbsp Trifecta+ fertilizer per gallon of soil
Instructions
- Hydrate your coconut coir brick and place it aside.
- Add one part worm castings to your mixing container.
- Use the worm casting bag or whatever you are measuring your "part" with to add in 2 parts of the coconut coir you set aside.
- Add in one half part both perlite and vermiculite.
- Estimate or measure how many gallons of soil you have and add 3 Tbsp Trifecta+ fertilizer per gallon of soil.
- Mix all ingredients well with your hands or a trowel. Now you have the best seed starting mix for your plants!
Notes
You can substitute the coconut coir for peat moss. You can also substitute the perlite and vermiculite for biochar. Add in kelp meal, blood meal, feather meal, or other organic fertilizer in place of Trifecta+.
Recipe variations
While this recipe is meant to be used for indoor seed starting I have used it for more than just seed germination. You can use this as a potting mix for house plants or for container gardening.
I did make this soilless seed starting mix because seed starting mixes that use soil can contain bugs and unwanted pathogens. If you are wanting to use this as a potting mix here is how you can change this recipe up.
Compost, top soil,
You can substitute the worm castings for compost or top soil if you are not using this recipe for indoor seed staring. Using these common ingredients can help you save money on potting mix.
Leaf mold
Another great way to save money on this soil mix is by substituting the coco coir for leaf mold. Leaf mold has many of the same properties as coco coir and you can make it yourself.
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