How To Make Your Own DIY Potting Mix & Garden Bed Soil

Here at Frosty Garden, we make a lot of our own soil.

Making your own garden soil is a really easy process.  It’s really just a matter of combining ingredients in certain ratios.

At a certain scale, making your own soil can also be much less expensive than commercial soil bags you purchase at the store.  Herein we’ll teach you our techniques and methods that we use.

When you understand the components of a good garden mix, it can open a lot of doors for you.  You will know how to improve practically any soil that you might be working with.

What Characteristics Make For A Good Potting Soil?

This is probably a good starting point for the discussion.  Dirt is not great for gardening and potting soil or garden mix is not necessarily “just dirt.”

There are some characteristics that you want to see in a good quality potting soil or garden mix.  In general, a quality soil that will help your plants thrive has the following characteristics:

• Plenty of nutrients for your plants initial growth
• Drains water well / Non-clumping
• Retains moisture
• Healthy pH for plants

Good quality potting soil will compress together and hold its shape, without breaking apart.  It should also crumble apart with only a small amount of effort applied.

What you definitely don’t want to do is dig up a bunch of dirt from your yard and try to use that in your garden!  Your average dirt will have none of the above characteristics and will offer you more troubles than it’s worth.

It’s important to point out that what is commonly known as “garden soil” is also not usually great for the purposes of growing plants.  Garden soil can be used as an element in a soil mix, but it shouldn’t be used exclusively.

Don’t Worry Too Much About Soil pH!

We were hesitant to even mention pH, simply because that can turn a lot of people off from making their own soil.  “It sounds complicated!”, they’ll say.  We agree.

Here’s the thing.  Plants are quite good at growing in soil that has a fairly wide pH.  The image below shows various pH and the generally recognized ranges where a plant can take up those nutrients.  Wide bars are good, narrow bars are bad.

Will your plants grow a little bit better with the perfect pH?  Sure.  Will they also grow just fine if the pH is a little off?  Yes they will.  You have a pretty wide range to work in if you’re growing common garden vegetables.

With the ingredients we discuss here, the main one you have to worry about is sphagnum peat moss.

Peat moss has a lot of benefits.  It will provide bulk, it breaks down slowly, it retains moisture and it promotes good soil drainage.  But, peat moss is naturally acidic and will therefore tilt your DIY soil towards acidity.

If you want to correct the pH, you can do so by adding dolomitic lime, more commonly called garden lime.  You can also find calcitic lime, which is basically the same thing with more calcium.

There are two types of these lime products out there, powdered form and granular form.  Powered forms will tend to correct the pH more quickly, whereas granular variants will correct it more slowly.  For that reason, granular variants are generally considered safer to use.

In general, consider adding the following amounts of garden lime to soil that uses peat moss:

• 1 Tbsp per gallon (4 liters) of soil mix, or
• 1 (heaping) cup per 15 gallons (60 liters) of soil mix, or
• 3 (heaping) cups per 50 gallons (200 liters) of soil mix

Other than that, you don’t really have to worry about pH.  In many cases, you could probably even skip this step and still be just fine!  Again, this is about trying to get optimal pH and not about just getting plants to grow.

Example DIY Garden Soil Mix Recipes

Here are a few of the garden soil recipes that we know about and have also used.  We use the “part system” so you can decide what quantity you want to make.  That way, you can base it on gallons, liters, buckets, bushels, or dump trucks for quantities.

Mel’s Mix from Square Foot Gardening

• 1 part compost (from 5 different sources)
• 1 part vermiculite
• 1 part peat moss or coco coir
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Frosty Garden’s “Secret Weapon” Potting Soil:

• 2 parts compost (typically homegrown, sometimes commercial)
• 1 part peat moss (locally sourced when possible)
• 1/2 part vermiculite
• 1/2 part perlite
• Greensand per manufacturer recommendation
• Biolive per manufacturer recommendation
• Azomite per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

General Potting Soil

• 1 part peat moss or coco coir
• 1 part compost
• 1/2 part perlite
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

DIY Potting Soil

• 2 parts peat moss or coco coir
• 2 parts vermiculite
• 1 part compost
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Homestead Potting Soil

• 2 parts peat moss or coco coir
• 1 part compost
• 1/2 part vermiculite
• 1/2 part worm castings
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Garden Soil Based Potting Mix

• 1 part peat moss or coco coir
• 1 part garden soil
• 1 part compost
• 3/4 part perlite
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Houseplant Mix

• 2 parts peat moss or coco coir
• 1 part perlite
• 1/16 part sand (approximately 3/4 cup per gallon of mix)
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Cactus Mix

• 3 parts peat moss or coco coir
• 2 parts sand
• 1 part perlite
• 1 part vermiculite
• Fertilizer per manufacturer recommendation
• Garden lime, if using peat moss (~1Tbsp per gallon of mix)

Example Seedling Mix Recipes

If you’re looking to build your own seedling mixes, there’s a number of different approaches that you can use.  All of these will work for germination and raising baby seedlings.

One important thing to observe is that these are all “low nutrition” soil mixes.  They are not designed for long term plant growth.  Rather, they are best used for initial germination with a plan to transplant your seedlings to more substantial soil once they are established.

You’ll likely see a lot of similarity between the recipes.  The differences are mostly about the drainage performance of the soil, which is highly beneficial for germination purposes.

When we build seedling mixes, we strongly prefer using coco coir over peat moss.  The reason for this is that its slightly less biologically active.

We have some additional notes on the sterility of seedling mixes below.  This is a difficult process to perform in a DIY fashion, so sometimes commercial mixes are beneficial to buy.

High Drainage Seedling Mix

• 2 parts coco coir
• 2 parts vermiculite
• 1 part sand

Premium Drainage Seedling Mix

• 2 parts coco coir
• 1 part vermiculite
• 1 part perlite (fine, if possible)
• This is our generally preferred seedling mix!

Low Adjunct Seedling Mix

• 7 parts coco coir
• 1 part vermiculite
• 1 part perlite

Super Basic Seedling Mix:

• 1 part coco coir
• 1 part vermiculite

Seedling Mix

• 2 parts coco coir
• 2 parts vermiculite
• 1 part perlite (fine, if possible)

What About Making Your Own Seedling Mix?

One of the most important characteristics of seedling mix is that it’s sterile.  That means that it’s completely devoid of life.  We are also speaking in terms of microbiology, nothing is alive.

Sterile can be difficult for the home gardener to achieve.  It can be done in the home, but it requires certain treatments.

In general, we would advise most gardeners to purchase seedling mix instead of making their own.  Almost all commercially available seedling mixes are sterilized.

Seedling mix is not often needed in extremely high quantities, either.  Only a CSA farm, or other major food producer, would have the demand needed to make your own seedling mix make sense.

We buy our seedling mix, despite having every one of the needed ingredients on hand.  We go through a large bag every two years, so it’s not worth our time to make it.

If you want to sterilize your soil, steam is the best technique to use.  What we recommend is heating your soil with steam to about 140-160 degrees Fahrenheit and holding that temperature for at least 15 minutes.

There are other techniques out there, but this is the safest method that will ensure good results.  If you’re reading about putting soil in your oven or microwave, do yourself a favor and don’t do it.

Should You Build High Quality Potting Soil For Raised Beds?

We think this is a good question and the answer is that it’s entirely up to you.  It can be quite costly to purchase all the supporting materials to fill such a volume.

We made our own soil for our beds (using our “Frosty Garden secret weapon” described above) and can tell you that we spent hundreds of dollars on the soil for our beds.

We looked at our soil as a long term investment and wanted our beds to produce intensively for years to come.  Our raised beds produce every kind of fruit or vegetable incredibly well, so it was worth it for us.

What we can tell you is that we’ve seen people experience a lot of troubles with trying to fill beds inexpensively.  Almost everyone that does it “cheap” has regrets afterwards.

How Much Soil Do You Need To Make?

Warning:  MATH!  If you don’t need to learn how to make complex soil quantity calculations, feel free to skip this section.

It’s usually a good idea to figure out how much soil you will actually need.  This will help you when planning out how much material to purchase for your project.

In our experience, figuring things out by the cubic foot has been the most accurate method that we’ve found.  (You can do this in metric, too, but the math will be slightly different.)

Most of the products you might purchase are sold by the cubic foot, also making this very easy.

Here are some reference numbers that you might find helpful:

• 1 gallon container:  0.13 cubic feet
• 5 gallon bucket:  0.69 cubic feet
• 10 gallon grow bag:  1.3 cubic feet
• Raised bed:  Length (ft) x width (ft) x (height (in) / 12)

As we know, we need different quantities of different materials.  You can fairly easily determine how much of each material that you need.

For our example, we’ll assume you are filling a 4 foot x 10 foot x 1 foot raised bed and you’re using “Frosty Garden’s Secret Weapon” soil mix.

First, figure out how many cubic feet of total soil mix you would need:

• 4 foot x 10 foot x (12 inch / 12) = 40 cubic feet

Then, determine the recipe’s total number of parts:

• 2 parts compost + 1 part peat moss + 1/2 part vermiculite + 1/2 part perlite
• Simple addition gets us to 4 total parts in the recipe

For each material, divide the total cubic foot volume needed by the total number of parts in the recipe, and then multiply by the parts needed of each material:

• Compost:  (40 cubic feet / 4 parts) x 2 parts compost = 20 cubic feet
• Peat Moss:  (40 cubic feet / 4 parts) x 1 part peat moss = 10 cubic feet
• Vermiculite:  (40 cubic feet / 4 parts) x .5 part vermiculite = 5 cubic feet
• Perlite:  (40 cubic feet / 4 parts) x .5 part perlite = 5 cubic feet
• Total:  40 cubic feet!

In the event you are ordering materials by the cubic yard, you can figure that out too!  Simply divide the total cubic feet needed by 27 to get the number of cubic yards.