What is the cheapest yet best way to make your own potting soil?
Thanks
Clayton

I found a couple recipes online.

BASIC MIX
6 parts sphagnum peat moss or coir
1 part EACH perlite & vermiculite
Combine & water until moist, then add seeds.

SOIL-BASED MIX
1 part EACH peat moss OR mature compost
1 part EACH garden loam OR topsoil
1 part EACH clean builder's sand OR perlite

ENRICHED MIX
4 parts sphagnum peat moss
2 parts compost
1 part perlite
1 part vermiculite

Start with whatever pretty-good mix you can afford or afford to make.

Then make it half as expensive by mixing it with an equal or greater amount of screened bark - inexpensive pine bark shreds, fines or small chunks (grit-sized, up to around BB size). Bark will hold a good bit of water if it is too fine (smaller than 2 mm).

Coarse bark makes fine mixes LESS water-retentive and BETTER AERATED if you add gritty-size shreds, like larger than 1/10 inch or 2.5 mm.

Pine bark breaks down slowly, like a year or more for fines, and several years for coarser chunks.

It won't cause anywhere near the nitrogen deficit that wood does in similar sizes, because bark breaks down slower and has some nitrogen itself.

You said "cheapest", so screen your own bark to the right sizes, starting with the cleanest bark mulch or other bark product you can find - pine, fir or balsam are best.

"Mulch" from my Home Depot is all soggy, smelly, dirty logyard trash. I only buy from Lowe's now. Lowe's had some pretty clean mulch, and VERY clean "fine pine bark NUGGETS".

Try to get bags that were never stored outside in the rain. Once they soak up water, they go into aerobic fermentation and produce toxins like organic acids and alcohols (bad for root hairs). And anaerobic microbes are NOT beneficial microbes in soil for gardening.

Screen it with hardware cloth, like 1/4" and 1/8". It can go faster if you use coarser screens to remove big stuff first. Then you can chop up the big stuff with a clean lawn mower or chipper, and re-screen that. Or use the coarse stuff as top-dress mulch.

I lay hardware cloth over some steel shelving I found, and lay that on top of wheelbarrows. Then push the bark around with the back of a rake, or prop the shelving on a slant and "pour" the bark down the slant.

I re-screen several times with different size mesh. I wish I had some 1/16 inch mesh to test! I read about someone who uses window screening (24 mesh!) to "de-dust" his bark fines.

If your store-bought or self-made "good" mix is finer than you need, screen the bark to be coarser. Try to get rid of dust and fine bark fibers. Keep sizes from 2mm to 4mm (ideally).

If the store-bought mix is already more than coarse enough (I never saw that happen), screen you bark to be a little finer.

If the store-bought mix is about coarse enough to have good drainage and very good aeration, screen the bark so you don't mess that up. Keep some fine stuff (1 mm) and plenty of gritty stuff (1/10 inch to 1/8 inch or 2-3 mm).

Perhaps test the bark you've just screened by filling a tall pot and soaking it well. Water should run out the bottom freely and leave the pot only somewhat heavier than it was dry - not HUGELY heavier with excessive retained water.

If the pot retains to much water, it has few or no air spaces left. Oxygen and CO2 can only diffuse in and out fast enough if they find some air-filled pores to diffuse through.

Gases diffuse literally 100,000 faster through a gas than through water!
A water-logged mix drowns roots and kills potted plants.

Well said, Rick, as usual!

Roots need oxygen & moisture at the same time to function. When there is only moisture, (because particles are so small that they fit closely together with no air spaces between,) roots suffocate and rot (overwatering.) When there is only air, they shrivel and die. An ideal mix is one that is plenty of air in it while moist.

Whatever kind of soil or mix one has , NOT packing it tightly into the pot can help preserve tiny air spaces.

Vermiculite collapses when wet. I wouldn't use it for anything but starting seeds. Perlite would perform oppositely, and is a helpful addition for maintaining more oxygen within container soil.

A good soil is more about its' texture and particle size than the actual "ingredients" used. Over time, organic bits decompose into smaller bits, so even the "best" soil, if it has organic components, will need to be replaced when this happens. The speed at which this happens depends on many variables, but on average, about 1-3 years.

I agree with everything Tiffany said.

>> Whatever kind of soil or mix one has , NOT packing it tightly into the pot can help preserve tiny air spaces.

I agree you can't just "tamp it down" tightly, the way you might stomp on the soil around a tree or bush that you just planted outdoors in dense soil. especially in a pot.

But when I try to "add air" to the soil in one of my outdoor raised beds, I do a little "firming" of the soil after amending with chunky stuff and compost and then "fluffing it up".

Here's my theory: after I fluff it up with a garden fork, the soil is very loose and maybe as much as 30% air in large pores. But it's unstable. Just the weight of soil and mulch would soon compact it down too much, and rain or watering would make it slump and run together horribly like thick soup or thin pudding. The clay would "dissolve" and run down to fill ALL air gaps. The clods that were barely supporting each other would collapse and lose their structure.

My theory is that I need to firm it down "a little" so that clods touch semi-firmly without air spaces collapsing, and big chunks have a chance to sit upon each other and "lock" into place. It seems to me that once it has been "firmed" a little, the remaining large air spaces (15%??) are more stable and the clay seems more inclined to "stay in place" inside clods or peds, instead of turning into soup.

If true, it's another of those darn gardening "Goldilocks principles", like in the story "The Three Bears".

The porridge had to be not too hot and not too cold. It had to be "just right".

But what the heck does "just right" mean? If you don't already know what "just right" feels like and looks like, and how to create and maintain it, what good does it do to know that something needs to be "just right"?

In gardening, it seems as if everything is the "Goldilocks principle".

Seed-starting mix has to drain well enough to stay aerobic, but can't drain so fast that the seeds dry out between waterings. Potting mix (and garden soil) also need to hit that "golden middle", balancing drainage and aeration against water retention.

Soil has to be "fertile enough" for the current crop, but no mineral may be concentrated enough to hurt root hairs. Total soluble minerals can't be excessive or the plant will die of salinity. Over-fertilization kills plants, and under-fertilization slows their growth.

You can't overwater, or roots drown. You can't under-water, or plants will sulk and wilt.

Each plant needs the right amount of sun. Even plants that need "full sun" may not be able to take "full sun" in a Texas or Arizona summer afternoon.

Temperatures have to be warm enough but not too hot.

Day length has to be long enough, but nights also have to be long enough. Sometimes you even need daylength to be in creasing or decreasing - by just enough.

And experienced gardeners give advice as if we "just know" what is "just right", like Goldilocks apparently does.

I think that gardeners who learned by watching an experienced gardener are incredibly lucky. They were able to see and feel what was too compacted, over-watered, over-fertilized or burned by the sun.

Those things are hard to put into words. The closest I've seen is explanations that stick to "operational" definitions.

"The soil is too heavy IF you squeeze a damp handful of soil firmly and it clumps into a hard ball.
It's too loose if it falls apart when you open your hand.
It's just right if you have to poke it a little firmly before it crumbles.
it doesn't drain well enough if water runs off the surface during a rain.
It drains too fast if plants wilt one day after a good rain.
It's too hard if you try to push a shovel into the ground and the shovel blade bends."

"Operational" definitions say to do X, then look for Y or Z.

That tries to avoid the need for you to be Goldilocks ... except that it does require you to "just know" what is meant by "damp", "firmly" and "hard".

I think most of us who did not learn at our mother's knee have to learn by killing plants and guessing at the reasons.

"They all died ... maybe they were over-watered!"

"Hmm, they all died again, maybe this time it was over-fertilization."

"Hmmm, they lived until they turned into 6-inch-tall spindly stems and then all fell over dead. Maybe not enough light?"

Don't know if you can access this without being a member of Cubits, and Al Tapla's cubit in particular, but he posted a great article on container soils here: http://cubits.org/containergar...

I agree with RIcCorey and purpleinopp. I buy a decent potting mix (12$ huge bag) then further cut it with fine bark ($4 huge bag). I use Kambark from the Ace stores here on the East Coast (elsewhere too?) Seems kind of silly to buy all the special ingredients just so you can make good potting soil? You can buy some excellent potting mix if you hunt for it. (Fafard made a good one, are they still around?)
Do read tapla's advice for understanding of what makes good soil.

sallyg said:... I use Kambark from the Ace stores here on the East Coast ...

Thanks, Sally! I'll have to check Ace. They're lots closer to where I live than Lowe's is.

I got sick of paying such a lot for potting mix a while back and bought some of a cheapo brand that was at Lowe's. In the long run, I'm now sure it cost me more than the good stuff would have because everything I potted in it died. Guess I should have known because of how heavy the bag was, there was too much sand in it, and not nearly enough good stuff. It compacted immediately. Anyway, now I do buy the "good stuff" - it says it's all organic which means it's probably too moisture retentive - and stock up when it's on sale. I always lighten it up some by adding Perlite too, but that doesn't really save any money because Perlite isn't cheap either.

Btw, if you buy bags that have been torn and are leaking at Lowe's they sometimes mark them down for you. (I carry an old towel in the back of my car to put plants and leaky bags of soil on . .. just shake it out into the garden when you get home to clean up)

My method for getting the right density in the pot is to pour potting mix in the pot, water it and let it drain. Add the plant, pour more potting mix around the plant, water it again and let it drain. Keep adding potting mix until it's at the right level for the plant, watering and letting it drain. I don't ever tamp or firm the soil by hand any more. Too variable.

sure thing, anything for an old compost buddy.
Their 'mulch' one here was the very small pieces.

Elaine, I hear you on that cheap potting soil from Lowe's. Yeck! Everything I potted in it died too, but it was mostly Stella d'Oro daylilies. I've since learned what makes a good potting soil from RickCorey, Purple and Tapla among others. with what everyone said above. Clayton, you can learn to avoid making some of our mistakes, by asking questions and experimenting until you're satisfied with what works for you. A soil mix that works for a dry environment like California or Arizona, will not work for a humid and wet one like what we have on the east coast. Be sure to read Al Tapla's thread, it has some very good information in it. And ask more questions until you're comfortable with your homemade soil. Also, check with your local nurseries to see what they are using, and ask if they will sell to you from their stock. If not, ask them to order the ingredients you need to make your own soil.

I have made my own potting medium for years. I use 2 parts peat moss, 1 part compost (NOT manure), and 1 part sand. I've had great luck with it......nothing has croaked from that........maybe from poor care on MY part.......... but not the potting medium.

I've been making the 5-1-1 container mix aka Tapla Al's for years now and it works great. I'm too lazy to do the screening part, but try to look for good sized bark to use. Some years it is harder than others to find it. A bale of peat moss, a 4cf bag of coarse perlite, fertilizer, and a bag of garden lime last a long time. I just need to buy pine bark most years. Much cheaper than any commercial mix, and the plants are much healthier. You need to water more regularily than with those "moisture mixes", but you won't have the root rot and stunted growth that you often have with those. Similar high quality commercial mixes are available at nurseries, but are very pricey here.

For starting seeds with wintersowing I use regular potting mix though, preferably compressed bales of ProMix when on sale. The 5-1-1 isn't good for seed starting. It stays so loose that it falls away from the roots of seedlings at transplant time.