If it is "standard" bagged potting soil, it very likely contains no real soil at all - most bagged potting soils are soil-less mixes that contain peat, bark, composted something or other (choices vary) and some drainage additives - sand, perlite, pumice etc. Since there seldom is any real component attributed to what is considered 'soil', it will not test out the same way that garden soil will and so a rather pointless exercise.

The good news is that potting soils tend to be very well draining, at least when fresh/new, as good drainage is a key requirement for container plantings. Over time however, most lose that fast draining ability as the composite particles tend to breakdown and compress. No good reason NOT to add to any existing garden beds - adequate drainage properties still remain intact for that purpose - but not a very good choice for further container planting. Better to purchase fresh potting soil for that purpose :-)

What she said! They do break down, both mechanically and biologically, so the coarse barky shreds that create good drainage aren't there, and it becomes much finer textured. Sometimes I blend some of the old stuff into the new, especially for the bottom of a very large pot (such as for patio tomatoes).

I have no idea how to evaluate your sample for actual particle size though.

Are you preparing for potted plantings or for in the ground?

Mostly preparing for potted plantings (in 12 half-barrel container planters) and perhaps for some ground level beds also. My thought/intent was to perhaps mix/incorporate a suitable amount of compost in with this 2-year-old potting commercially produced potting soil (Happy Frog brand) rather than having to purchase more of the commercially produced stuff. The compost I'm considering adding/incorporating would be discussed in the thread linked below (horse manure, leaves, and produce trimmings) to hopefully replenish nutrients and improve aeration/drainage. Comments?

Here is a link that might be useful: my intended compost

There is much written about this kind of thing on the container forum. Growing in a pot and growing in the ground are very different, and rarely would one have success with the same soil for both. Something much more chunky than peaty potting soil and compost would be much better for containers. Bags of mulch 'from last year' are one of my fav ingredients for home-made potting mix. I wouldn't put anything from that jar in a pot.

The bigger the container, the easier it is to do such things, but generally, potted plants don't obtain their nutrients from the soil, but from periodic top-dressing of compost, compost tea, some type of fertilization. This can sometime be successful for short-term plantings, but usually it's either too fertile and makes plants ill, or the fertility runs out long before the season is over. It's virtually impossible to maintain healthy, live soil in the closed environment of a pot.

What do you plan to grow?

Planning to grow flowers. Typically already started nursery flowers. Not sure what kind yet.
The stuff in the jar is what I have a "ton" of and is what the flowers were planted in last year in the containers. I don't have any "bags of mulch from last year" as ingredients from which to try to make home-made potting mix.
I'm a little confused by the statement " Something much more chunky than peaty potting soil and compost would be much better for containers." Are you saying the old potting soil (like which is within the jar) would be considered peaty? And/or that adding the compost mixture (as discussed in the link I posted above) to the potting soil would not be chunky enough for container growing?
I'll browse the container forum too, thanks for the suggestion/reply.

Are you saying the old potting soil (like which is within the jar) would be considered peaty? And/or that adding the compost mixture (as discussed in the link I posted above) to the potting soil would not be chunky enough for container growing?

Yes! Your current potting soil is most likely peat based, so of a pretty small particle size. Adding compost is really not much of a benefit as it will continue to breakdown and its particle size will decrease as well. The more uniform (and small) the particle size, the more fast drainage is compromised. And fast drainage and good aeration - the spaces between the individual particles - are key to successful container growing. To refresh existing potting soil, I'd suggest you add bark fines, sometimes sold as soil conditioners. You can add a small amount of compost as well but don't get carried away. The best potting soil is one that is very textural and durable, so with a range of both large and small particles and of material that is less inclined to decompose or breakdown rapidly.

That's pretty much what I would say to that except that I do try to start with a mix with no tiny particles. They lodge into all of the spaces, preventing oxygen from being able to permeate.

At this time of year, it's sometimes possible to find mulch for sale that's been there since last year. Most years, I try to stock-up so I'll have some that's aged all winter in bags to use for 'potting soil.' When I use fresher mulch, there can be issues with chlorosis. I believe this is why bark is often chosen for making a fresh mix, which would have much less risk of nitrogen-robbing that can be encountered with fresh wood. Bark would be more durable as well, as mentioned above, decomposing more slowly.

I didn't realize the significance, especially for container growing, of having good aeration and space between the particles and fast drainage. Per the suggestion to look in the container forum, I did, and came across the thread linked below which discusses this in pretty good detail. It seems for one thing that bark pines (as mentioned/suggested this thread also), specifically pine bark fines 3/8" or so in size are recommended to incorporate into the soil. It seems apparent I should seek out some such commercially produced bark fines and purchase it but I was really hoping to avoid too much expenditure. Also, the old potting soil (as shown in my jar photo) it's hard to know whether the particle size is too small to consider re-using as a "base' to which to add the bark and maybe some compost/fertilizer in an attempt to "renew" it.

Here is a link that might be useful: water retention thread

Yes, you've found a good bunch of info there. There are so many extremely helpful discussions on that forum, I didn't want to limit you to just one. As you have time, keep reading, that's how people get to know these things.

Then, when spring FINALLY comes, you get to go try it. You'll have some success, some failure, and do better each time, as long as you keep trying to improve, you almost surely will. Think of how far ahead of the curve you are in what you've already learned compared to those who've never given a minutes' thought to 'dirt' and how it's necessary for it to be 'good' to have 'good plants.'

Kudos to you for making compost, BTW! You may find this short vid lecture about soil microbiology helpful in regard to ground gardening. It might sound intimidating and boring, but she talks in plain language about things that about any gardener should be able to apply to their yard.

Okay thanks purpleinopp for that link, and for the encouragement too. In one of your posts above you did say you wouldn't put anything from that jar (my photo) in a pot. Absolutely? Even if were to incorporate plenty of proper aerating medium, plus maybe plenty of compost consisting of aged horse manure and leaf/produce compost? Reason I ask is because I have so much of it (the old potting soil as in the jar photo) and would like to maybe re-use it after "renewing" it if that's even reasonable to consider.

This post was edited by sgull on Fri, Jan 24, 14 at 14:49

If you want to grow ornamental plants for 1 season, it may be worth a try. I know you've said what's in there, but if I haven't used the same jar of stuff, amended the same way with the other same stuff, I would really be just guessing. Going by the appearance, it looks like it's all silt and sand. So I'm still in the same position about it, I'd put it on beds, on the ground, and find something else for pots. Assuming I had the $ to do so. Am I going to do that myself? *mostly.* I'll be mixing some old, some new, to try to save also. It's easy to say a thing, not always possible to do it.

What is the cost of the plants that will go in the pots? Is it OK to spend that money on them if they don't do well? Might you really prefer fewer plants that look better (from the smaller amount of 'good dirt' you wanted to spend $ on?)

The longer I garden, the less I enjoy tending pots and pretty much stopped using them for seasonal flowers. If I put the flowers in the ground, they almost always outperform. The number of pots I devote to tropical plants that come inside for winter is part of this decision - like that's enough to tend, but I think it's just not a good use of my money, for all of the 'soil' and these kinds of plants that would almost always look better in the ground.

There's also the way that most flowering plants need tons of sun. So they dry and need to be watered often, which takes up my time watering them, and sets up the organic ingredients inside for decomposing as quickly as possible, radically changing the soil composition quickly. If you're using tap water, that's a more constant application of chemicals, and the PH is usually well above what most plants prefer, slightly acidic. Baking in the sun also causes the soil in pots to be much hotter than the ground. Having roots get this hot is not something plants really enjoy, some won't tolerate it. This can be moderated somewhat by having trailing plants flowing over the edges, sitting smaller pots around larger ones, using light-colored pots, not sitting them on pavement or concrete, locating where there's 6 hours of sun but the rest of the time is shady.

That's my mindset and opinion about getting my most personal enjoyment from the small amount of money I'm willing to spend on seasonal garden decorations. Summer is a long, miserably hot experience here. Where the season is shorter, less brutal temps, most of these things would be less severe concerns.

Just remembered an analogy that help this make sense to me a while back. Imagine a pot full of peas. They're all round and the same size, and don't lodge perfectly together. There are relatively large spaces between them. Imagine how fast water will flow through, and how much oxygen will be in the pot after the water finishes flowing. Now imagine if a few ounces of sand were poured in. Water a few times. Where are the particles of sand now? Filling every crevice between the peas at the bottom of the pot. Do you think water will flow through as fast? How much oxygen is between particles of sand?

Ideally, you're after a pot of moist peas...

Yes that's plenty to consider of course such as costs of plants, seasonal or perennial, costs of purchasing various amendments and how often replenished, labor/time involved with tending pots, etc.
I might mention that in my growing zone (6, SE Alaska) we have a relatively short season and never brutally high temps and definitely not any excess of sun. So although tending pots is has been explained generally going to be more time/labor involved than ground beds, the pots are what we happen to have (a bunch of them at my workplace and I the higher-ups seem to want to use them), so for now I'm trying to get handle on the soil situation and having them work out decently for the flowers.
In the picture here I'm showing a container with a metal screen on the bottom. I'm trying an experiment with my old potting soil to try to judge its water retention. The container is 16 inches high and I put 8 inches or so of the old potting soil in it, then watered it with one gallon of water using a watering can. The container is sitting in a big tub where I can later observe/collect how much of the water infiltrates down through the soil in a particular amount of time. I plan on posting back here with results for followup.

So far, I've noticed, after measuring, that in one hour just about half the gallon of water poured onto the this soil in this container as described has infiltrated through.

Any comments please on the results of my soil drainage test? Anything appreciated. Thanks...

LOL! I bet you don't have issues with baking brutal heat in AK, good for a chuckle though, TY!

Drainage isn't as much about water-retention or lack thereof, as it is about the speed at which water can move through it, and whether or not oxygen can be present when it is moist.

If the whole bottom of the container is screen, excess water couldn't possibly pool inside unless a drain saucer/tray causes that. I'm not sure I understand the experiment, but it sounds like all you can decide is how much water your soil can hold.

To perhaps clarify, I had placed the container (with the screen bottom and the soil) into a larger plastic tub which captured the all the water that infiltrated through the soil. The screened container was placed so that the bottom of it was up an inch or so from the large plastic tub, so that the water that dripped through would stay separate from the soil in the container. That way I was then able to monitor/measure how much water infiltrated through.
So, if a half a gallon (out of a full gallon poured on) of water infiltrated through that deep of soil in one hour, could that be considered "well-drained" soil?

You are trying to see something that is not there. Soilless mixes, such as you are testing, lack the mineral portion of soil needed to see texture.

My measure of drainage is very unscientific. I use the hose to water plants when there's no rain to catch. The hose runs at about 2 gallons per minute. If water runs through pots as fast as it's coming out of the hose, I'm happy with that.

In response to the last two posts:
I'm actually uncertain whether the particular potting soil of I'm fairly certain is the majority of the soil I have, would necessarily be considered a "soilless mix". It's this stuff: http://foxfarmfertilizer.com/index.php/item/happy-frog-174-potting-soil.html I happen to have quite a lot (approximately 40 five-gallon buckets of it) a few years old and already used in outside containers for growing flowers. I suppose it's well past it's useful life but I'm just wondering about the possibility of trying to "renew" it with whatever amendments might be appropriate, instead of just either throwing it out altogether or having to buy a whole batch of new stuff to mix it with.

With container planting, should the rate of drainage I would usually want to achieve be to have water run through the pots as fast as it's being watered? How about half as fast? Still not fast enough?

Thanks for any further comments.

Happy Frog Potting soil is indeed a soil-less mix - there is NO mineral-based garden soil in its composition. Unfortunately, it is not considered a very high quality, durable potting soil as it lacks the necessary textural components to provide these characteristics. I would consider it good for only a season or two at best - no longer without significant amendment. And that means amending with sufficient particle size and durability, like the bark fines and perhaps Turface (high fired clay) or pumice.

It is difficult to make a good judgment call about container drainage just by how fast the water runs through the container. That can be governed by pot size and pot material as well as time since last repotting and how rootbound the container might be. It is how long the media in the pot itself stays moist after watering and how anaerobic this slow drainage might become. There is also the issue of aeration and pore space, which is completely separate from drainage but plays just as significant a factor in container growing.

Personally, I would add your already used Happy Frog soil to any current garden beds and start over with fresh, new potting soil of better quality.

There are many regular posters in the Container Gardening forum that would highly recommend against reusing potting soil from one year to the next, never mind using it multiple seasons. If you consider your soil the foundation of your gardening activity, then it is important to invest wisely in the quality of that soil regardless of whether it is inground garden soil or container potting soil.

Okay thank you very much gardengal48 (and the others here too) for those very helpful replies which give me plenty to consider as I my try to get on the right (or at least get off the wrong track) soil-wise for these containers.

Adding larger particles will not mitigate the smaller ones. If water is flowing through quickly, air should be able to too. Moisture + lack of oxygen = root rot. Moisture + oxygen = healthy plant.