I completely disagree with whomever told you 'purely organic' was feasible. I think it's just the opposite. Inorganic fractions have longer lasting structure than organic ones. You can grow plants in containers with a 'purely organic' strategy, but reusing the medium year after year is going to present serious problems as the organics turn to anaerobic muck. The media with the most long term stability are going to be the more hydroponic ones. I have plants growing in what is known as the Missouri Gravel Bed mix which is 2 pea gravel : 1 calcined clay. I've also used LECA and the very popular 'round these parts Gritty Mix as well. I reuse it by placing old media in a tub of water to let the organics like roots and such to float to the surface. Then I pour of the water and organics and can reuse the MGB media at the bottom. It will effectively last forever. The same can be said for scoria, pumice, and LECA.

You are going to get a lot of recommendations for Gritty Mix. You can definitely count me as a fan of it. I think it's very easy to use.

I live in a very short season, low-night temperature climate, so I grow peppers and eggplant in containers. I can start them indoors, the soil warms much quicker, and the yield is 3 or 4 x what I get in the garden. So I have a 'fleet' that consists of 40-odd 2 to 7 gallon containers.

I've been 'recycling' my potting soil for years now. I began with standard potting soil mixes, added some very rich pond soil for trace minerals, and each spring, I tip them out on a concrete slab, smack them with a shovel, pull out the roots and shake the dirt off, and then add another few bags of fresh potting soil and some home-made compost, mix the whole thing up, and refill the pots.

What happens is that the perlite, those small inert white bits, and other inorganic components continue from year to year, while the organic part decomposes and disappears. So you end up, as the years go by, with a lighter and more 'airy' soil.

Following this forum for a few years, I have increased the bulk/structure of my potting mix by adding pieces of beetle-killed pine bark - I burn the wood for fuel, so have an abundant, free supply of bark thats perforated with tiny beetle holes, which the pepper plant roots just love. This year, I'm up to about 1/4 by volume pine bark. This summer, I intend to compost a few cubic yards of pine bark, see if I can incorporate that in my mix as well.

I also threw in a 40 lb bag of Azomite into the kitty for more trace minerals, again from reading on Gardenweb.

So, yea, you can do it. Look for an initial mix that has a lot of perlite. As you go along, keep in mind that you can't just slosh away with the water 3 times a day like you could with one of the fast draining mixes, you'll end up with an anaerobic mess. Pay attention and only water when they need it, and when the plants are large - 3 ft high pepper plants - towards the end of the season, that can be every day.

This post was edited by david52 on Mon, Apr 8, 13 at 23:20

Yeah, but you still have to bring new media in yearly and remake the mix, David.

Also to the OP, potting medium is the most expensive part? That's crazy talk as far as I'm concerned. I use free composted 'mulch' from the city and big bags of perlite. Potting medium can be cheap.

Where I live, a 6 cubic foot bag of perlite is $45. 2 cubic foot bag of good quality potting soil (Fox Farm) costs $20, the cheap stuff (peat and Miracle grow) $10.

I'd have to calculate how many cubic yards of potting mix I use every year. I add cubic FEET of fresh potting soil/compost a year to cubic YARDS of recycled potting soil.

If you can find free materials for your potting mix, I'm glad it helps you cut costs. Unfortunately such isn't the case for me.

I also live in a small and rural area, so I can't find the stuff for my soil less recipe locally in large. quantities (i.e. by the cubic yard).

The soil less mix I use is the 5-1-1 mix; it uses pine bark mulch, spaghnum peat, and vermiculite as the base.

Somebody recommended replacing the vermiculite with compost; I make the recipe in 30 gallon batches (that's what a large batch yields) and it calls for 5 gallons vermiculite. Would adding that much compost cause the
soil less mix to absorb too much moisture?

Also my concern is they said reusing a soil less mix, it would reduce in volume over the course of the initial growing season that it's being used. I'd have to replace what eroded somehow, how could I do this economically?

The only thing I can really get in large quantity is
the peat moss, it's abut $11 for a 4 cubic foot bag.

My concern about the gritty mix is that it would drain too fast. I've used the 5-1-1 mix and any veggie that needs consistent soil moisture when setting blossoms/fruit hates it, cause it dries out too fast.

Also I don't know where to find the ingredients of the gritty mix, and I am not really sure what the terminologies for the mix as is mean.

Maybe the best way of looking at recycling container mix is: you're not so much recycling the nutrients, you're trying to retain/recycle the 'structure' - which allows enough air penetration so you don't end up with an anaerobic mess.

Perlite holds up year to year. Some commercial blends have volcanic pumice, rocks, sand, whatnot to build structure. Pine bark, at least the landscape mulch size, holds up pretty well. So be on the lookout for inexpensive structure components.

Peat, compost, manures, and - in my experience, vermiculite - disintegrate into dust after a season or two.

So its a question of getting enough volume of this 'structure' stuff to recycle. The broken down organic matter, or dust, comes along with it - there is still plenty of plant nutrition in the organic 'dust', but as the over-all volume inevitably shrinks, I add / top off every year with fresh compost, fresh potting soil, etc.

It's an investment - like the containers themselves.

The vermiculite and peat are two major components of my soil mix and are common ingredients in other soil recipes I've found.

What can I use in place of the peat and vermiculite to retain the structure of the soil? Like you suggested I will probably end up using pine bark mulch. The variety I'd use would be double shredded the kind I get locally is just too big in size and causes the soil to dry out too fast.

If the size of the pine bark mulch is small will this cause the mix to break down or will it still retain it's structure?

Also since you said manure/compost tend to break down, what can I use as a substitute for them?

I'd use synthetic fertilizer but I've heard the longer it's the soil, over time that salts build up as a result.

I am sorry for the double post but how much compost would I need to replace the compost/manure that shrinks?

The soil mix I'm debating using is ...

1 part soil (potting mix, I'd using something like Pro Mix or Miracle Grow; would this be suitable for container gardening and in a mix to reuse)

1 part Compost (I'd not be making my own it would be commercial compost)

1 part peat/vermiculite (since you said they'd break down, what are my options for a substitute)

Miracle grow is mainly peat already.

Al's 5:1:1 mix uses perlite not vermiculite.

The Gritty Mix is equal parts bark:gravel:calcined clay. The bark you have already said you can get. I would think gravel or chicken grit would be findable in a rural area fairly easily. Then all you would need is calcined clay which is also called Turface. Many people substitute Floor Dry from NAPA Auto Parts or stall-dry, which are diotamaceous earth products. The Turface is used for baseball fields which might help you source it.

Yes the Gritty Mix drains very quickly and you would have to water it more often. But, I'm in Los Angeles and I don't have a problem maintaining moisture with regular water.

With regards to synthetic fertilizer buildup, that is easily solved by flushing the containers with plain water occassionally.

Can we get a picture of your 5:1:1? I'm a little surprised that you are having trouble with moisture retention while using vermiculite instead of perlite.

I'm a fan of larger sized pieces of pine bark - they don't disintegrate very quickly, they contain some nutrients, they hold moisture pretty well, keep good structure, for me its free, and when I empty out the containers, the roots are all over the bark.

Here's a picture of some recently planted containers with small pepper plants, a Sharpie pen for scale, and you can get an idea of the size of bark that works well for me - as well, you can see that there's a fair amount of perlite.

TO clarify I thought the 5-1-1 mix was the mix I've used before; it wasn't I made a mistake sorry.

Below is a mix I found earlier which I'm debating using...

The pine bark fines/mulch I use aren't that big but there are still some larger pieces.

I found this potting mix (DYI) on the internet earlier.

Would I be able to reuse from year to year (NOTE: I am NOT making it as is, I'd be making adjustments to it based on the suggestions given here)

ORIGINAL RECIPE:

1 bucket (2-1/2 gallons) peat moss
1 bucket(2-1/2 gallons) vermiculite or perlite
A half bucket (1-1/4 gallons) screened compost or composted cow manure
2 cups fine sand
2 cups pelleted time-release fertilizer
1/2 cup lime (to counter the acid of peat and keep the pH level near neutral)
Mix thoroughly. Makes enough to fill two 14-inch tubs or five 12-inch hanging baskets. Double or triple recipe for bigger containers.

MODIFIED VERSION (As per suggestions given)

1 bucket (2-1/2 gallons) pine bark fines/mulch
1 bucket(2-1/2 gallons) coarse vermiculite (to absorb water)
A half bucket (1-1/4 gallons) screened compost or composted cow manure
2 cups fine sand (or perlite, for drainage)
2 cups pelleted time-release fertilizer(Osmocote)
1/2 cup lime (to counter the acid of peat and keep the pH level near neutral)
Mix thoroughly. Makes enough to fill two 14" tubs (how many gallons would this be per batch)

Also I'd be tripling it for larger containers (have 45 gallon ones)

Here is the tripled measurements...

7.5 gallons pine mulch
7.5 gallons coarse vermiculite
3.75 gallons compost
6 cups sand (or 4 c perlite)
6 cups pelleted fertilzer (would use Osmocote)

Have three questions about the mix...

Would it be suitable to reuse from year to year. If I have to ammend by adding more compost the following season, how much would I need to add per tripled batch?

Is it too heavy on fertilizer? I don't want huge fruiting plants (rampant in growth...i.e. tomatoes, peppers, melons etc.)
and no fruit

Should I reduce the fertilizer or is it not too much?

holy cow David those are some big pieces of bark!

Thats bark from beetle-killed pine trees, 4-5 years old. Its riddled with tiny holes, and the cambium side is covered in assorted fungus.

When I empty them out at the end of the season, the bark pieces are just covered with rootlets, growing in every possible hole and crevice.

I would say that definitely qualifies as making the best of a bad situation. I have family in CO so I know what the bark beetle is doing out there. yeesh

The soil mix I plan to use is the one listed above. Would it be suitable for being reused?

Regarding the size of the pine bark mulch, it would be either single or double shredded (this is the initial use before it decomposes over the course of the growing season). Would this be too small?

One batch of it makes 6 gallons. Is it too heavy on fertilizer?

If I were to make a triple batch that would be 6 cups of pelleted fertilizer. Should I reduce the amount of fertilizer?

controlled release fertilizer is typically added as 1 pound of Nitrogen per cubic yard.

I don't know what to tell you. I wouldn't use that mix at all much less reuse it. Fine sand isn't a replacement for perlite. I mean they aren't even anywhere close to the same particle size. I have found fine sand to cause drainage problems not help with drainage. Vermiculite breaks down quickly and you want ingredients thatdon't break down quickly if you want to reuse it.

kawaiineko, have you read this post about container soils yet?

Container Soils

5 parts pine bark fines (partially composted fines are best)
1 part sphagnum peat (not reed or sedge peat please)
1-2 parts perlite
garden lime (or gypsum in some cases)
controlled release fertilizer (if preferred)

The 5-1-1 mix is very similar to the mix I currently use.

The mix I use is basically the same ingredients just in different quantities.

Unfortunately how much Osmocote (which is what I use)
would I use? It doesn't specify.

If I were to make a 30 gallon batch (which is the quantity I normally make my current soil mix in) how much lime and fertilizer per batch?

Also could I add a little bit of compost to the mix without having to worry about it breaking down?

I would most likely use double shredded pine mulch as I can find it in bulk at a decent price.

However if I use double shredded mulch, then would I not be able to reuse the soil mix?

Basically does it really matter what size the pine mulch is?I'

The fertilizer is going to be added at a rate of 1# nitrogen per cubic yard. That's elemental nitrogen so if the NPK ratio is 10-10-10 the fertilizer contains 10% by weight of elemental nitrogen. That means you would have to add 10# of that fertilizer per cubic yard. A cubic yard is about 300 gallons.

Yes it does matter how big the bark is. Large pieces will drain faster than small pieces. David gets away with those big pieces because the surface area is unusually high due to bark beetle damage. But also because he has a bunch of fines that hold water and he restructures the medium each year to counteract the collection of fine water retentive particles in the bottom of the container. I wouldn't recommend people use bark that big normally.

Some people stretch the 511 to two or three seasons and then make new batches and chuck the old ones into the garden. It seems to be the consensus around here that after three years there is significant degradation of the medium that justifies replacement. I make new every year and use the old batches as topdressing for permanent perennial beds or as an amendment to vegetable beds that don't have enough organic matter.

Kawa, I would most definitely not use the soil recipes you have posted. It would be a very labor intensive way of drowning all plants, I'd guess.

Al's gritty mix is perhaps the most reusable, especially if you will take it, wash off all the inorganic parts and re-add new bark. Doing it in all turface or all perlite would also work.

But what you're describing is a swamp, basically.

I'd suggest you study the 5:1:1, and the rationality behind why it's good -- and then go ahead and replicate with replacements if you feel like it.

I adjust the amount of all three components based on plant needs as well as how often I intend to pay attention to that pot. Upping the peat will obviously increase moisture, as will using smaller perlite bits; upping the bark or perlite will obviously decrease moisture retention. Replacing peat with coco coir or whatever other potting soil changes the dynamics, etc.

But reusable for years and years -- no...but given how cheap bark is, it's been incomparably cheaper for me to make 5:1:1 than the fancy soils around. I bought a 3.8 cu ft bale of Pro-Mix for $40. I'd pay $48 for the same amount of Eden Valley Blend. For that price, I could have bought 32 cu feet of fir bark, and toss in 1 part of peat and perlite, both quite economical -- and you have a really cheap soil. Now the amount of space these big bags take up in my tiny storage --- at real estate prices here in SF, THAT is considerable lol.

Grace