Generic topsoil in bags from Wal-mart. Then mix a small amount of FINISHED compost into it. We have a local organic researcher who used that blend as his base.

Sounds good to me.
You can mix up some manure with shredded leaves in the fall also.

You might wish to consider something that will ensure better aeration and significantly less compaction and water retention than any mix with topsoil as a significant fraction. Aeration, drainage, and water retention are all directly linked to particle size and your soil is comprised of ALL fine particles, which means it will be difficult to grow in, with your watering.fertilizing technique critical because of a very narrow margin for error.

Consider trying

5 parts of pine bark fines
1 part sphagnum oeat (coir if you must)
1 part perlite
1/2 cup dolomitic (garden) lime/cu ft
for a well aerated mix that will make life much easier and your plants much happier.

AL

Here is a link that might be useful: In greater depth if you click me.

There are potting mixes available that do not contain any peat moss and are made of finely ground bark or sawdust. There are also coir, coconut hulls, based potting mixes although you may consider the fuel used to bring that material from where it begins here as unsustainable, and that by continuing purchasing coir we may be robbing the soil where it is produced of organic matter they need.
I have successfully used compost that I make as a growing medium in containers although there are those that will simply tell you it cannot be done.

Read Al's link :-) No one is saying compost can't be used in container culture -- only that it provides rather unsuccessful results for any kind of long term situation. Would certainly skip any garden soil as a component for the reasons Al mentions, but also because you can bring indoors outdoor problems - insects, diseases, weeds.

The most important thing to remember is that growing plants in a container puts a very different set of circumstances into play that one does not encounter in inground gardening. If you realize and understand this and develop your mix to address these issues, you will have much better results.

Reading the link will help.

Lol - it's not as though I haven't done my homework. ;-) Coir and CHCs have inherent problems that make them less than ideal as a large fraction of container soils. Salinity, an extremely high K content, and a pH that precludes the use of dolomite as a Ca/Mg source are some of the issues. Sawdust is inappropriate because of the heat it generates during the composting process, it causes N immobilization issues, and there is usually a very high pH spike at some point during the composting process. Whether 'finely' ground bark will offer any relief from the high water retention of peat/coir/compost.topsoil-based mixes depends on HOW finely ground it is, which brings us full circle to how important particle size is to our getting the most from our plants insofar as how media choice effects growth and vitality.

If compost came in large particles and was stable - there would be no reason not to use it, but since it only comes in tiny particles, compacts easily, and ensures excessive water retention, it's easy to make the case that if you DO use it as a primary fraction of the soil, you're leaving potential growth and vitality lying on the table.

It's true there's more than one way to skin a cat, but there are also good ways, better ways, & not so good ways to skin the same cat. I realize many of us have ideologies we feel we must work within, but that doesn't change the realities that settled science puts in front of us. A lack of aeration in our container soils is probably the largest obstacle the average container gardener faces in his/her quest to optimize growth/vitality. In my years here at GW, I've seen literally thousands of people turn their growing experience around by simply making a change to a soil that ensures ample aeration for the life of the planting and a soluble fertilizer that delivers on cue. It's literally that easy. ;-)

Al

Thanks for your link Al, I read it all.

I think there are small pine barks at Petco, where the pets go. They are for reptiles. Probably 20 dollars for a 10 pound bag.

I think I would replace peat moss with brown leaves.

Many of my pots are clay, so I am wondering if that changes the persistance of the perched water table. My pots seem to dry pretty fast.

And why do you add 1 part perlite, it seemed like in your writeup it didn't have much of a use unless it was 65-75%.

Thanks,
mushroomrockets

The pine bark you see in the picture at 3,6 and 9 are all suitable for either the 5:1:1 mix or (when screened) for the gritty mix.
{{gwi:2389}}
The bark you're referring to is screened white fir bark (seen at the top of the picture), and a considerable overkill for the 5:1:1 mix (center of the picture), but great for the gritty mix.

Most are able to find suitable pine bark for under $4 for 2 cu ft, which will make about 18 gallons of soil when mixed with the peat & perlite.

The perlite adds some volume to the soil and reduces water retention, but when combined with the pine bark flakes it holds the flakes of bark apart & helps create channels and macro-pores too large to hold water in the soil. These pores remain filled with air, and provide an excellent home for healthy roots. Roots don't like the 'wet' conditions of heavy soils. They prefer damp conditions where ample air in the soil ensures good root function & metabolism, and where roots can absorb water in vapor form and molecule by molecule from damp colloidal surfaces. Strangely enough, "WET" hampers the absorption of both water and the nutrients dissolved in water and limits growth. The greater the amount of time your soil remains damp instead of wet or dry, the better the potential for increased growth & vitality.

Soils with large particles that hold water internally, and large macro-pores that are sure to remain filled with air, are extremely healthy. Your cost comes in the form of (usually) having to make them yourself, and in the need to water a little more frequently, but the rewards are, as noted, considerably greater potential for optimum growth/vitality and a much greater margin for error in the areas of watering and fertilizing.

Getting back to the perlite question ...... perlite is only 1/7 of the mix, but added to the other large (pine bark) particles, together they comprise 6/7 of the mix, which is about 85% larger particles (not allowing for the very fine pine bark that is usually 5-10% of the bark's volume).

Terra cotta is gas permeable, so it allows byproduct gasses as well as water vapor to pass through it's walls. The additional evaporation does reduce the length of time the PWT persists in any soil when compared to pots with impermeable walls. If you know the PWT disappears from your soils within a couple of hours, not much damage to roots s being done, but if you have parched water lasting a day or more (and many heavy soils see PWTs persistent for many days) you're definitely leaving growth/vitality lying on the table.

AL

Thanks for your response -

So why does outdoor soil not need these kind of amendments? Is it just the continual supply of organic material and biological activity that makes the difference in soil structure? My gut wants to try to mimic this in houseplants.

I feel like your mix would have you watering more often, and maybe fertilizing more often, because it seems like there isn't much soil chemistry going on in there to tie up and slowly release nutrients, nor much to absorb water. I guess that's what the coir/peat is for, but I don't want to use either of these. What to do, what to do..

So why does outdoor soil not need these kind of amendments?

The answer to that question has a couple of parts. First, outdoor - garden - soil is well....soil :-) It has a complex mineral and organic make-up and an active and diverse biological population. Garden soil is alive and is a constantly circulating system, receiving inputs from the atmosphere, from the plant and animal life it supports and typically, from the one who gardens it. Sometimes it does need amending - to loosen heavy or poorly draining soils, to replace organic matter, which is often consumed in greater quantities than is created naturally, to augment naturally occurring trace or microelements that are present in insufficient levels (or to neutralize those that are present in too high a level) and sometimes, to supply necessary plant nutrients that have been used up by dense and rapid plant growth that often occurs in a cultivated garden or agricultural situation unlike what occurs under uncultivated or natural (wild?) growth conditions.

Growing plants in containers is significantly different. First, it is pretty close to a closed system - free drainage is highly restricted by the confines of the container. Because of this, the requirement for fast drainage is ramped up, encouraging the use of very durable and textural materials as a growing medium. Usually (hopefully) there is no 'soil' involved, so the active biological component of a garden or outdoor soil is missing. Attempting to encourage populations of typical soil organisms by adding organic matter - their natural habitat and food source - is counterproductive because these types of materials decompose quite rapidly and as they decompose, they reduce in size. A reduction in particle size - when most of the particles in a container "soil" mix are the same small size - eliminates or reduces the spaces in between the particles (the pores) where oxygen is held and where water is able to pass freely. Lack of porosity or aeration reduces the ability of the media to drain freely and when that happens, whatever is growing in that container suffers from both lack of oxygen and excessive or persistent moisture.

Yes, containers do need to be watered often and do need to be fertilized often and for the reasons you surmise - the recommended materials allow water to move very quickly through the medium and there is very little soil chemistry happening because there is really no soil and minimal organic matter and therefore biological activity. But it is a trade off to accommodate the ability to grow plants in what is a highly useful and efficient but extremely unnatural manner.

Can you fudge on all of this?? Replace durable, slow to decompose and textural ingredients like bark, peat, coir, perlite, etc. with plain ole slow draining, moisture retentive garden soil and/or compost and skip the daily watering and the fertilizing and just hope there is enough of a biological and chemical function to provide necessary nutrients? Sure you can........but you are very likely to wind up with plants that are not very happy, not flower or produce well or even live very long.

It's your choice.