Potting mix is pricey, and it’s only getting more expensive – but the good news is, you can make your own much more cheaply. A standard bag of all-purpose potting soil costs around £8 (USD $10), and at 40 liters in volume that works out at the princely sum of 20p (25c) per liter, which soon adds up when you’re filling lots of containers.
So today I’m going to share three home-blended potting mixes that will all prove considerably cheaper than bought-in mixes, and can be made in minutes. The ingredients can be either picked up at any garden center, or found right in your own garden. Let’s get started!
Budget-Busting Potting Mix From Your Garden
In the spirit of saving a pretty penny, let’s start with the cheapest mix of them all! This is a general-purpose potting mix ideal for those on a strict budget, and suggested by none other than the Royal Horticultural Society. It’s ideal for bigger or longer-lived plants such as trees, shrubs, and perennial flowers. The best bit is that it costs very little to make – and could even cost you nothing at all!
The bulk of this budget-busting mix is simply garden soil. You can take it from several spots around the garden so you don’t leave a big-old hole in any one place. Soil will add weight and stability to the mix, making it ideal for plants that will be in containers for years. Make sure to use soil from areas that are broadly free of weeds to reduce the risk of weed seeds being in there, and definitely avoid areas containing perennial weeds, which can be a lot harder to get rid of!
If you happen to have any molehills in your garden – you lucky thing! Molehill soil is like gold. It will have a lovely crumbly texture because those handsome moles have sifted the soil for you. What obliging fellows!
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Homemade leafmold or compost mixed with garden soil is free and provides everything established plants need
To add nutrients and open up the structure of the potting mix, we’ll need to add some organic matter. This could be garden-made leafmold, well-rotted manure or some lovely garden compost. I’ve also got some grit, for a very specific reason.
In most cases you’ll only need soil and organic matter for this mix, using an approximate ratio of seven parts soil to three parts organic matter. But if your soil is like mine – a heavy, claggy clay which doesn’t drain well – you’ll need to reduce the soil element of the mix down to six parts, then add one part grit. On the flip side, if you have a very free-draining sandy soil that dries out a little too quickly, you might want to swap out one part soil and replace it with organic matter, giving six parts soil to four parts compost or manure to improve water retention.
It doesn’t matter what you use to measure everything out, so long as you’re consistent – it could be a cup for smaller quantities, or a bucket for a bigger load.
The only cost in this mix – to me at least – is the grit, which brings the total cost to a mere 7p (9c) a liter. But obviously if you’re not using the grit then this has the potential to cost you nothing at all!
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Coconut fiber is sterile, helping seedlings get off to a trouble-free start
Supercharged Seed-Starting Mix
When you’re buying a pre-made potting mix, you’re partly paying for convenience. But, as I hope I’m showing, it really doesn’t take that much effort to make your own. And that especially goes for a seed-starting mix, which is simplicity itself.
My straightforward mix uses just three ingredients. The bulk of the mix is coconut fiber, which is produced as a byproduct of coconut farming, Coconut husks are shredded to a fine texture to create a product that is both light and sterile, so there’s far less risk of seedlings getting clobbered by fungal diseases, molds or fungus gnats in those more vulnerable early stages. You could use your own garden compost as the base to this mix, but I just reckon it’s safer to use something completely sterile when plants are young and vulnerable.
My other two ingredients are perlite and vermiculite, and both offer huge advantages. Perlite is expanded volcanic glass. It’s a bit like popcorn – it’s heated up and then explodes out into this lightweight, almost polystyrene-like texture. It is completely sterile and really helps to open out a potting mix. It will improve drainage by stopping our mix from slumping down and getting compacted.
Vermiculite is also lightweight and sterile, and also made by heating something up, in this case a naturally occurring, mined mineral called magnesium-aluminum-iron silicate. Its texture is like a layer of flaky pastry, and these layers can absorb and hold onto both moisture and nutrients. So while the perlite will keep the mix from getting too wet, the vermiculite will keep things from drying out too quickly; we want a bit of both.
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The addition of perlite and vermiculite elevates this homemade seed-starting mix above commercial offerings
For this mix, we need seven parts by volume of sifted coir to start. Sifting it helps remove any stray bits and pieces, and any longer strands that will just get in the way of emerging seedlings.
Then add two parts by volume of perlite. Mixing perlite creates a bit of dust, so you may want to wear a mask for this step to avoid breathing it in. To finish, add one part vermiculite. Mix it well. Using a large mixing vessel like a big bucket or even a wheelbarrow or similar makes this easier, so you can properly turn and evenly incorporate the ingredients.
The total cost of this mix is summarized below. It’s a lot cheaper than your standard seed-starting mix, and yet it doesn’t scrimp on the good stuff. The inclusion of perlite and vermiculite makes it a genuinely superior product to many of the off-the-shelf mixes.
This seed starting mix is very low in nutrients, but that’s absolutely fine because all the nutrients a seedling needs early on in its life come from the seed itself. They won’t need any extra nutrition until they have their first adult leaves, maybe a week or two after they’ve germinated, at which point you can move seedlings on into my next mix: a fantastic, all-round potting mix for just about any use in the garden.
- Coir/Coconut fiber: 7 parts - 15c/11p per liter
- Perlite: 2 parts - 34c/25p per liter
- Vermiculite: 1 part - 40c/30p per liter
- TOTAL COST PER LITER: 21.3c/15.7p per liter
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This all-purpose potting mix gives plants everything they need to really thrive
Homemade All-Purpose Potting Mix
So next up is my all-purpose potting mix, which is great for potting on seedlings and for container-growing most vegetables and annual herbs. I’m using a formula that makes use of garden compost and adds a few goodies for additional nutrition to help support plants (including seedlings, young plants and veggies) for longer.
Sift your garden compost to remove any lumpy bits and give a finer texture in the end product. Any woody bits can either be used in the bottom of larger containers, to part-fill them, or simply tossed onto the soil as a mulch around growing plants, so nothing’s going to waste.
Start with two parts by volume of compost, then add two parts coconut fiber and one part perlite to further help with drainage. There’s no need for vermiculite in this mix because the compost will do a good job of holding onto moisture.
Now you could leave it at that – there’s good drainage courtesy of the perlite and it’s nice and rich thanks to the compost, but by adding a few more treats we can really supercharge this mix. A good handful of volcanic rock dust (also sold as azomite) will help to encourage microbial life in the mix and is a great source of trace elements and minerals that will be released slowly over time, creating a vibrant and alive mix that roots will love to tuck into.
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Perlite helps to open up a homemade potting mix and allows it to drain more freely
Worm castings (literally worm manure!) are another fantastic source of nutrients which, along with the garden compost, will help to inoculate the mix with all sorts of good things. If you can’t get hold of worm castings then you could try kelp meal or seaweed meal instead, which will really help to stimulate growth.
Below are the final figures for this mix. The volcanic rock dust and bought-in worm castings aren’t cheap, but the volumes used are so small that the overall cost impact is minimal, which makes this genuinely outstanding mix come in at nearly half the price of pre-mixed potting mixes. Beautiful stuff!
