I prefer straight composted leaves for potting too. But it you want the fiber-rich texture, IMHO, mixed yard clippings. small twigs chipped finely, which have some green growth on them. If no green on them, add grass clippings.

I think you guys are both way off the mark, and Glib is setting himself up for a soggy soil that will collapse quickly and some intense N immobilization with the addition of materials that break down rapidly, not to mention the extra heat associated with rapid composting.

When you think of container media, think STRUCTURE. Forget about the soil's ability to feed the plants (that's monkey easy) and focus on it's ability to hold the right amount of water and air. Compost can't do that. No matter what you THINK, using a large compost fraction (or any other fine material like peat, coir, sand, topsoil ----- is going to provide you with a soil that retains a soggy layer at the bottom after a thorough watering. This is what you DO NOT want, because water/nutrient uptake is an energy driven process that requires fuel (photosynthate) fuel to be burned in the presence of O2. W/o the O2, there is no way to drive the process and the plant suffers for as long as the O2 level in the soil is insufficient.

Ideally, you would BASE your soil on a very larger fraction of coarse material that retains it's structure for long periods (is mineral in composition or breaks down very slowly - like pine bark). This coarse material would comprise more than 75-85% of the volume of the medium. You could then add a small fraction of compost, peat, or a mineral like Turface to adjust the water retention to a favorable level. Adding coarse material to "amend" finer material doesn't work because the fine material simply fills all the air space between the large particles, leaving you with the same drainage, aeration, and soggy soil level you would have had using only the fine material.

The idea is to create a soil that holds all or most of it's water inside of soil particles - on the surface of soil particles - and at the interface where soil particles contact each other, and none or little of its water between soil particles. That's not achievable using compost, peat, coir .......

Al

Leaf mold can retain too much moisture so it is not a good media for potting soil. I have used finished compost as potting soil for years with no problems, although others seem to.

bummer. next year plantings will collapse then.

I would recommend adding coco-coir with compost half and half you get all the benefits of water retention of peat moss with not acidity or fungus gnats if you bought a bag of it. adding some pearlite to it will give it air and good drainage.
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Coir + compost = excessive water retention (simple physics - due to small particle size) and a higher probability of gnat infestation than when using soils that drain well and are well-aerated. Also, coir has a very high pH, a very high K content, and often high salinity. Adding perlite to the mix doesn't improve aeration or drainage until there is so much perlite that the volume of coir+peat is so small it can't fill the air spaces between the small particles. Think of adding perlite to pudding ....... how much do you have to add to improve aeration and drainage? The same holds true for the peat/coir mix.

Al

Hi ...

I just want to get some green things growing on my balcony. All the mixes are so complex, and I have a bunch of bags of potting soil, and don't have the time to run around to various suburban garden suppliers to get bark fines and such. What is the best thing I could add to potting soil? Peat? Coir? sand? Compost?

My school garden used a combination of compost and coir for bottom watered buckets and things grew very well, but I'm not using a bottom watering system.

I'd love to plant grasses, canna lily, and some echinacea.

Thank you!

What Pam said ...........

In order to AMEMD your potting soil, you'll need to add enough bark or stable coarse material so the fine material doesn't fill all the air spaces between the larger particles. Obviously, you can see in the mind's eye that the larger particles need to make up at least 75-80 % of the soil's volume. That's why you can't amend a water-retentive soil with bark or perlite. You'd need to add far more than 50% coarse material, which would mean you're actually amending the coarse material with the fine particulates. If you want to get the most from your efforts, focus on basing your soil on coarse material and adding only enough fine material to achieve a reasonable amount of water retention. Understanding how water behaves in soils will do more to advance you toward becoming a green thumb container grower than any other single step you can take.

Al