fixing potting soil

This question is applicable to a lot more than edible crops, but I'd like to understand better about potting soil, whether for starting plants or for container gardening. I've been using the cheap Lowes potting soil for a few years. It looks to be largely organic stuff. That is, it isn't just garden "dirt". OK, so that sounds right. Nice consistency coming out of the bag. But I notice that this stuff basically turns into mud after a while. That is, after a long and very hot summer, when stuff is getting watered every other day to keep it alive, you dig out a plant, and find that the plant has been trying to grow in highly compacted and hugely soggy soil. This in a pot with excellent drainage. Just to get the soil out of the pot, you can't do it with fingers. You need a trowel to excavate it.
Now, this doesn't seem like the kind of stuff plants would like to be growing in. I should have realized this was happening, because during the summer, when I watered, it would sometime pool up in the top of the pots, and take an hour to drain!! The way I was taught, soil should absorb water, but be permeable enough to let it soak through.
I found a number of fat worms in it, so it can't be that bad, but ...
OK, my bad, using cheap potting soil. Butt head against wall, etc.
But I still have a few bags of it, and it seems to me that with appropriate amendments, this stuff could still work. What should I use? Coarse sand? Perlite? Vermiculite? Compost? Peat moss? Now, if I'm going to add organic material to it, I'd like it to be stuff that didn't eventually turn into the organic paste I seem to have ended up with.
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I don't know exactly what product you are describing when you say "potting soil". There are pre-packaged soils out there for seed starting that are light and fluffy; potting soils that are coarse and have small chucks of wood in them; and then topsoil that is mainly made out of decomposed organic stuff.
I am assuming that since you described it as getting clogged and muddy when watered but has a nice consistency coming out of the bag, then you must be talking about that cheap topsoil stuff that costs $1.00 per 40 lb. bag.
You could use perlite to fluff it up some, but that might be expensive to add enough to have a substantial effect. Sand is always good to help with drainage, but it doesn't decompose or add any nutrient value to it. Plus, it tends to carry downwards when you water and settle into a layer at the bottom of the pot--which might cause it to clog up the pot drainage holes later on.
What I normally do with my own potting plants is: 1) mix topsoil 1/2 and 1/2 with potting soil that has wood chunks in it (like the moisture control Miracle Grow stuff), 2) add in some slow release plant food, 3) shake it all up in a big trash bin in order to thoroughly mix up the contents, and then 4) put it in the pot with the plant.
If it is mixed right, you should be easily be able to transplant your plant later on. Just don't water it for a couple of days and the soil will shrink and stick together into one big cylinder. Afterwards, turn the pot sideways and gently shake out the entire block--plant and all. No need to damage the root system by trying to dig it out of the soil.
Angello
On Sun, 15 Nov 2009 15:02:24 -0800 (PST), Dwight Lassiter

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Thanks, that makes sense. Actually, it wasn't "topsoil", but that $4/ bag mix. Maybe "planting mix" instead of "potting mix"? Again, it appears mostly organic stuff because it's fluffy when it comes out of the bag, and for some weeks/months after using it. Would be a good trick to take plain topsoil and make it look that way. Good point about sand migrating downward in the pot. Had not thought of that. Also, the shrinkage, which I figured would be an inconvenience, does indeed have an advantage in removal from the pot.
I'm thinking peat moss is good for fluffing it up as well, but does that break down rapidly enough that you'd end up with the same organic glue at the end of a season?
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Peat moss is a pretty economical option (I think you can get a 2 cu.ft. brick of it for a couple of bucks) and will add fluffy-ness to your slow-draining soil. It's also great at holding water--I think it's able to retain about 20 times its weight in water. The down-side it that it also adds a bit of acidity to the soil. Check the plant's acidity tolerance levels before you do it. However, You can counter-act the acidity by adding in some lime. I don't know about how fast it breaks down though.
Another good option is to mix in composted manure. It'll add nutrients while it decomposes and aereates the soil. The downside is handling the odor if you are going to use it for indoor plants.
Angello

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Well, then I'm good to go with peat moss. I have irrigation water that is mildly alkaline. Water table is limestone based, which accounts for that alkalinity. So whatever my planting mix is made of, it eventually gets somewhat alkaline. Adding acidity is just the ticket.
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You can use tree bark ( preferably a fine grade ) to break up that soil mix. Like Peat, its acidic, but not as much, and decomposes slowly. 10-12 $ a 1/2 yard here.
Some of the Coir and Coco chip products are also a good admendment choice for small applications. The coir is ~ 3$ a brick ( makes approx 8 liters).
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I buy Perlite and Peat Moss to my black much also. The all organic stuff deteriorate so quickly that a level 5 gallon pot will sink 4 inches in a season. If I had a choice between the two, pick Perlite. The peat will deteriorate also - the perlite will not. Jim in So. Calif.
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Yes, that's what I assumed. Even the peat moss will eventually decompose, though the stuff is fibrous enough that some structure may remain. I just want some mix that will retain permeability for a few seasons. Certainly true that perlite (or charcoal) should help with that.
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Support structure aside, Perlite is pH neutral, charcoal pH will vary depending, but mostly it will be alkaline. Just be aware of what the specific addition will do to the soil chemistry and factor in your hard water usage.
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And in most of the Western US, the soil is very alkaline. Living in So. Calif., I do not want to add anything to my garden soil that is alkaline. Most mixed supplements are ph. balanced to be neutral. Jim in So. Calif.
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