How to Make Potting Soil

If you use a lot of potting soil when gardening, you know that you can end up spending a lot of money very quickly when buying it in bags. But buying the ingredients separately and mixing up big batches isn’t hard—and it can save you some money!

Especially if you find raised bed soil on a closeout sale like I did. We found these bags of Bonnie Harvest Select raised bed soil for $1 a bag at a local Home Depot. They were cleaning out their stock in early December, and we benefitted greatly from it!

However, the soil was too heavy to use in my large pots and my Greenstalk Garden. Here’s how I mixed in a few extra ingredients to make the perfect potting soil for my container plants—and how you can, too!

Step 1: Examine your base material

The first step is to examine your base material. My raised bed soil was pretty heavy—you can probably see what I mean by the photo below. While this would be great in my raised beds, it definitely needs lightened up a bit for my other container gardening.

If you’re starting with compost or something similar in consistency to what I have below, I recommend working with a ratio of roughly 1:1:1 base material, coco coir, and perlite. However, you can adjust this ratio as you mix up your potting mix and get the perfect consistency for what you’re planting.

I approach these things with a simple mindset: it isn’t rocket science. I eyeball a lot of what I do, so that’s what I mean when I said a ratio of “roughly 1:1:1.” It’s possible that the compost you start with will be super heavy, in which case I would recommend mixing in more coco coir.

Step 2: Moisten & add coco coir

The next step is to add in coco coir. Coco coir is a great and far more sustainable alternative to peat moss. It lightens up the soil and has a feathery texture that facilitates lightweight moisture retention and oxygen flow.

I ordered a set of coco coir bricks online because it’s more economical. I got 5 bricks on sale for $18.39, so about $3.68 a brick. To fill two tiers of my new Greenstalk planter, I used two bricks.

The bricks come compressed, and all you need to do is add warm water to expand them. I do this in a bucket, adding water and then scraping off the coco coir that expands until the whole brick has expanded.

Then I dump it into my mixing bin with the original raised bed soil and use a shovel to start mixing! Again, if the base material you’re working with is very heavy, you may want to consider working in more coco coir than a 1:1 ratio.

Step 3: Mix in perlite

And last I add in perlite. Perlite looks like small pebbles, but it’s a super lightweight volcanic glass. It also serves to lighten up the soil, improve air flow, and improve drainage. You can usually buy perlite at big box stores and local nurseries, but I find buying it in bulk to be much more economical.

Step 4: Store or use

Once it’s thoroughly mixed, you can use it! I don’t recommend storing it in an air-tight container because the moisture will leave to mold growth. you can put it in a tub like this, just leave the lid cracked. I put mine immediately into my Greenstalk tiers, so I didn’t have to worry about storage.

Also remember that bagged potting soils often some with a slow release fertilizer in them. Unless the base material you’re working with was compost or something with nutrients already added, you’ll definitely want to supplement with fertilizer or plant food or some sort. I love Liquid Seaweed for this, a jug lasts me forever!

Real-life cost comparison

Each of the tiers holds one cubic foot of potting mix (about 8 gallons). So, for 2 cubic feet of potting mix to fill two tiers of my Greenstalk, I paid about $13 total! This is much cheaper than buying the potting mix I usually use for smaller containers, Fox Farm Ocean Forest, which is 1.5 cubic feet for $25-$28 depending on where you buy it.

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