They are just a containerized gardening system so any container/potting soil can work in them. If you want to make your own custom mix, I'd suggest the 5-1-1 mix - 5 parts pine bark fine, one part peat and one part pumice. I use it in ALL my containers (except for cacti and succulents) and have for many years and grow great plants!

You can safely ignore any instruction that the mix should be at least 75% peat :-) Peat is too finely textured, excessively moisture retentive (can lead to rots), compresses and collapses well before the end of a growing season and needs a pH adjustment to alleviate the high acidity. Keep it on the low end of the mix. And no vermiculite, ever!!

Earthbox does list a wide range of "suitable" bagged potting soils so you might find something quick and relatively inexpensive there.

Hi,

Thanks for the reply. Yes, the EarthBox website is where I found the Blackgold Natural and Organic potting mix. The goal is to mix my own potting mix to save money.

This is from the Earthbox website:

The growing media should be Sphagnum peat-based (70%-95%) that contains perlite or vermiculite. It should be light and fluffy when dry, and spongy when wet. It should NOT contain any rock, clay, sand, or soil. We do not recommend using topsoil or compost.

So you're thinking I should go against the Earthbox suggestions and I would still be fine?

Yep!! That advice is contrary to just about any good container gardening resource. Vermiculite can absorb 3-4 times its volume in water but once fully saturated, collapses and compresses into a soggy sludge that will impede good drainage. Same with the peat - too fine, too absorbent and also very soggy when wet.....not spongy at all!

When you have water reservoir at the base, you for sure do not want a potting mix that will be overly water retentive!

70% peat based is required to enable it absorb humidity from below and wicked up to prevent root become dry. Earthbox giving ideal mix for busy people that sometimes forget on watering. That mix increase plant survivability. You can replace it with others that have similiar function. Cocopeat also able to wicked water so i think it's ok too, just make sure no less than 70% or bottom up water flow doesn't work and it will be just like ordinary container gardening.

Ekor Tupai-

Thank you for the reply. What you said makes sense but your advice seems to go against what gardengal48 suggested. She said "You can safely ignore any instruction that the mix should be at least 75% peat :-)".

Now I'm a little confused. I think I should probably go with the Earthbox recommendation considering I've always used Black Gold Natural and Organic which is on their growing media list of recommendations.

Of course you can use whatever you like. But ALL container soils will wick water up from their base.....that's just the way it works :-) An Earthbox is just a self-watering container so why would the soil mix need to be any different in that than it would need to be for any other self-watering container? None of which have any "requirements" for the amount of peat they contain.

The issue with that high a percentage of peat is that peat is excessively water retentive and tends to create a very high perched water table. A high PWT leads directly to root rots. And because peat has a such a fine particle size, it tends to compress and collapse over time, leading to even slower drainage and a higher PWT.

There is science behind this if you'd like to research :-)

You have 10 boxes so if you wanna try other potting mix, use 1 or 2 for experiment. Simple fact is worth more than thousand words of oppinion, even if it's sound scientific.

I have 30 Earth Boxes. It took me many years of experimenting to get the mix right. I started out with potting mixes that contained coir, forest products. compost and soil mix. I was not successful until I found a mix that fit the Earth Box mfg profile which included the heavy percentage of peat content. You can mix your own and it will work but for me with 30 boxes, too much work was involved. Our success came from using the Lambert Potting Mix which is an all organic product and comes in 2 cubic ft bags. You can experiment like I did to see what works but its very disappointing to have to discard expensive potting mix that doesn't work. We lived close to the inventor of the Earth box who had his research center in Ellenton Florida. He passed away in 2018, but personally knowing this man, I can see no reason he would want to give advice that would provide failure for people using his Earth Boxes.

Lambert is what I used to use until Home Depot stopped carrying it. Where do you get your? Thanks.