Container soil

Does anybody have a potting soil recipe without much in the way of inputs. I assume both native soil and compost, though most establishment potting soil recipes do not seem to include native soil. I imagine leaf mold, coir, rotted sawdust, probably redwood, would play a part?

Growing in containers really doesn't work very well for me;
from what I understand, mineral soil compacts very badly in pots
but no soil means little microbial life to assist plant growth, and organic matter compacts too...
Pot 'experts' generally recommend growing in a soilless medium and force-feeding plants artificial fertilisers.
I've got several pots of basil going, but it's a bit pathetic.
My pots have compost, coir, perlite, aged bark and a bit of soil.
I feed them with nitrogen-rich teas when I remember.

Thanks Leila- I remain a little puzzled in all of this. I realize many here have fairly large properties, and are understandably not involved or interested in container gardening. At the same time I would think many of the urban farming permie types would have inforamtion on this topic, but i am not able to find it on a Google search. I do not dispute anything you have said about this, but just in general wonder why there is not more info on this. I would assume if you were to till in compost to your large containers that that would reduce compaction. I understand the idea of no-till in terms of beds. But if the choices are to use only highly processed, if not artificial substances, for a potting soil versus adding compost that is turned on probably at least a yearly basis, I would opt for the latter. Obviously this would apply only to annuals being grown in containers

I should add that i have seen some examples of nitrogen fixers and other companion type plants fro vegetable producing container crops. I assume Daikon would be something to use to avoid compaction

using just compost and soil from your yard doest make good potting soil, unfortunately.
in a big garden in the ground its different, theres checks and balances in the soil, it works out great...but in the tiny pots it gets weird.

you can add some smaller amount of well finished compost and some native dirt, to regular bag soil.
also leaf mold, coir and sawdust, sure...but a big NO on redwood, which has a very peculiar pH. apparently a lot of commercial bag dirt has a lot of wood in it.
the best is the stuff thats mostly coconut coir, imo.

i have access to a lot of recycled bag soil here, people give it away by the truckload and so i reuse this. there are some places here people have drop offs and pick up sites for dumping used bag soil. craigslist is another place people list recycled bag soil.

i screen it through a large hole screen to get most of the roots out and re use it. i often mix in different things to make more of it...add some native dirt (also screened) maybe finished compost....and lately i have been experimenting with adding local moss and river sand. some people really like to grow in sand, the kind you can buy at a store in big bags.

moss and sand are pretty good for a soiless growing medium...but theres no food in this for the plants....so you would have to work that out.

The problem with container gardening is that it changes too much for typical soils to work naturally. The smaller mass heats and cools quicker, changing the microbial activity. They dry much quicker, requiring more frequent watering's which lead to compaction of the clay elements. The lack of worms and other critters mean the soil isn't being aerated. Using a tillage crop (like daikon's) between grows won't resolve the issue as by the time the root has fully decomposed and is releasing N instead of using it, the gains would be minimal as it would be compacting from the repeated watering's to maintain the biological activity needed to compost it. The uneven drying of typical soil composition causes a lot of stress on the roots as either the ends die from dehydration or root from being waterlogged. Root growth itself is significantly altered by the constraint of the pots, unless you're using a fabric pot which air prunes the roots, in which case they need more frequent watering to compensate for the increased evaporation.

If you look at it from the context of creating an artificial environment to grow in, it becomes clear that we have to adjust our techniques to mitigate the problems. Typically by adding an inert high carbon component, usually peat or coco, as they provide structure that doesn't compress and ensure even drying/aeration of the mix. Outside of them, high sand mixes can work but require a lot of watering as it won't retain much and fertigation as the CEC is very low. Which is a highly artificial system even though it uses local natural inputs. So the question becomes "what's the goal?", are you trying to mimic nature or produce food? If the goal is food production, looking at alternate high output, low input systems makes sense. Aquaponics are a good example of balancing artificially managed components to create a functional system that mimics nature. I'm guessing that's going the opposite direction of your interest.

You could try altering how you cultivate containers to mitigate the issues. Bottom watering or wicks will significantly reduce compaction. Using lots of mulch and keeping the pots cool would make a big difference by increasing the stability of the rhizosphere. It'll still be hard to maintain healthy growth but it would help, if going that root a strong ability to diagnose nutrient imbalances becomes essential.

Jacques Fortin wrote: Typically by adding an inert high carbon component,

I've been having better results with pots since I started using biochar as the carbon component. Also, I try to use as large a pot as practical for the given task, given what Jacques says about the smaller mass. Smaller pots also dry out quicker in the bright sun, and if you have forgotten to fill the saucer below the pot with water, well, there goes whatever you were trying to grow.

Biochar helps in multiple ways: CEC is better, beneficial microbes can find a home in it, and it retains water. A couple percent biochar gives noticeably better results, and studies have shown that the point of diminishing returns is well over 10 percent by volume.

You can make an organic container soil that will work fine!

I put redworms directly into my containers and they love life! I've kept a small population of redworms alive for the last year and a half in a two-gallon fabric pot.

You can grow in finished compost, provided enough aeration is there. I always add native soil to my composts, so yes it can be used.

My wife is having good results using Nature's Way - "Square Foot Garden Potting Soil & Mix." It's not cheap, but it's the best we've tried IMO. It always throws up a few Mushrooms & grows Moss in her herb pots.

I added biochar to my indoor garden this year and had good results, definitely increased the effectiveness of the worm casting top dressings. Unfortunately we had to move as the landlady was convinced the 45w CFL's were jacking up her hydro bill...

I wouldn't plant straight into the compost we make as it's too rich and the plants would be scorched. By the time it's diluted enough to be usable there'd be enough native soil mixed in to create compaction issues as the soil here has a high clay content. Obviously regional differences will effect what you can/can't do.

I'd like to hear more about keeping red wigglers in the pot Johnny Niamert if you don't mind elaborating. My worms are constantly devouring everything in sight, it's actually becoming an issue finding them enough food. I guess the lower moisture content of potted plants would slow their breeding down, can you give an idea of how many worms and what if anything you feed them?

Jacques. I always add some red wigglers to most any potted plant I have. They seem to live fine in the potting mix, but I usually mulch and top dress so they have some fresh stuff every now and again. I will add 5-10 worms to any freshly potted plant. I usually find cocoons and babies by the time the plant is finished.
I have some red wigglers that I kept in a 2 gallon smart pot. I was forced to move awhile back, and I loaded this pot with wood chips, compost, and leaves. I top dress with things like kelp, alfalfa, leaves, ground corn, and they slowly disappear. The worms are a bit smaller than in the wild, but they still grow/reproduce. I'm planning on starting a bigger bin soon, and I will use these to populate it.
I also always add red worms to my outside compost bins and all my compost has red wiggler worms and cocoons in it. I was just turning my pile a few days ago and the worms were still there after winter.

I have had good success with adding leaf mould. I have a good free source for this in out local land trust. It does come with some weed seeds but no big problems.

My mix is not sterile! In the spring I mix all the old container contents, leaf mould, finished compost, some sand and some broken pottery. Last year I added a chunk of rotting wood to the bottoms of the bigger containers and watered with diluted urine to good effect. This year, biochar!

Thanks for elaborating Johnny. When you say you say you loaded the pot with compost, wood chips and leaves, it got me wondering if the wood chips have tied up enough N from the compost to cool the soil enough to avoid burning the roots. Obviously it's purely conjecture as I have no clue what your compost is like and I'm assuming you've mixed them all together. Which would make sense, the wood chips would provide the inert mass keeping the mix from compacting while the worms provide a readily available source of nutrients independent of the other interactions. When you say you top dress, I assume you mean un-composted raw material?

If you can't plant into your compost, it is not anywhere near finished yet.

There's too much variability in how compost is made to make blanket statements. Could you elaborate on how unfinished compost is releasing too much N, causing the plants to burn? Typically unfinished compost lock N up as the microbes use it to break down material, not the reverse by releasing too much.

Good information. Thanks to everyone. A little controversy here and there, but I love hearing the different experiences. I am hoping to do quite a few pots , at least 20+ gallon containers. I plan on using a variety of techniques to try to be experimental. I will probably do a couple of containers of store bought compost with perlite and coir, compost with some other combos which include peat, leaf mold, bio-char, worm castings or conifer shavings, and then some mixes that include compost with some native soil, from what I have seen more than 30 percent is probably too much, with some of the other ingredients mentioned. I have a couple more questions if people have time. I have watched some bio-char YouTube video, but have had trouble finding information in general. The conferences put on for bio-char have not included video or audio as far as I can tell and that has been a disappointment. It seems bio-char can come in several forms, so I am confused about what appropriates proportions of it would be in a mix. Some folks seem to say it is a replacement for perlite, so, in that case, I would assume you might go up to a quarter bio-char in a mix? If anyone can suggest a site, a book, or an organization with accessible information on bio-char i would appreciate it. The other subject I am pretty hazy on is wood chips. I usually hear redwood or cedar and that it should be chipped or shaved down to a certain size and that perhaps it should be composted. Thanks again

P.S I rent and have a pretty large patio area with bricks, so that is the reason for containers. I have considered growing right on top with the bricks with the bottom of containers removed, but I am concerned it would stain the bricks and perhaps not make that big a difference in terms of aeration and drainage. The bricks are not fancy by any means, So I am might try a small area and see if I get stains. And I am growing vegetables if I have not made that clear

I made some vertical garden barrel planters with 48 pockets on the side.

I'm planning to use a mixture of sand, soil, rotted wood, compost, and biochar. In the center "column" of the barrel, I plan to use about 30% activated biochar and either a log or bundle of small logs and branches to act as a sponge.

Really though, 55 gallons is a lot different than 1 gallon which is what you are talking about.

If I was dead set on indoor/patio/small space production, I would take a hard look at aquaponics.

I'd definitely second going vertical with container gardening as it takes advantage of the container to maximize space, which will increase your yields.

I don't have enough experience using biochar Matt, but here's a good source for more info. http://www.biochar-international.org/biochar/faqs#q19

Thanks Jacques and Luke Vertical is something I should think more about. Took the short course on aquaponics up here a couple of years ago. He is our N California guru, and i am a wanna be aquaponics type. It is a little complicated my reasons for going this way. First off am also an aspiring activist trying to provide my neighbors and townfolk some hopefully good info on how we might organize around local food and health, and healthy consuming. You know the kind of thing idealists waste their time doing. Anyway from that perspective, I feel a little compelled to have actually done some of the basics before telling any one else. Modeling a productive space for container and intensive gardening might be a better model, or a more practical one, the aquaponics from this perspective. But I will move it up as priority from this, and others who praise aquaponics as the way to go on hardscapes Second to that I also have some concerns about how the local farmers market here works


I had discounted vertical since things are going to be pretty stacked side to side, but for summer months around the solstice it should work well.

I am somewhat resolved to buying vermiculite and Peat Moss at least. I am wondering about minimizing the amount of soil by trying to plant in shallow containers probably only 3 or 4 inches. I have only seen something like that for the large growing trays that are 8 by 4 ft or something. anybody see a problem with that strategy

The shallower the container the quicker it will dry out.

Maybe you could do fewer larger containers?

Understood. I would be interested in using deeper pots as well. I assume you can muulch the surface of the container soil to improve on the soils water retention ability. Not sure what might help below the bottom of the medium

I did earth box style wicking containers and Mel's square foot mix (1/3 peat/coir, 1/3 vermiculite, 1/3 compost/organic) this year. We will see if the water reservoir helps with stability.

In a former place I used sand and a little clay instead of vermiculite to save $$ and it worked great in a raised bed garden, but I wouldn't want to have to move a container of it!

Thanks R Scott. I am not clear what the reservoir idea is, so if you could add to that I would appreciate it. I have heard for some folks that using pallets can be a good idea. I would probably add some height with some additional 2 by 4, or possible using some of the existing pieces I tear off of to increase the height of the pallet. Then line it with shade cloth to hold in the soil

http://www.instructables.com/id/how-to-make-an-earth-box/

An earth box is a brand of small wicking bed. The idea is the soil pulls the right amount of moisture up to the plant and the plant grows down to the water.

Mine are done in big round tree pots so they "look pretty"

There are dozens of ways to make wicking beds, depending on the size you want. search them on youtube and you can get a lot of variations based on the size you want.