So I think I have a good idea of how to add organic matter to the various projects that I've mentioned above.

In a year or two I should be able to generate enough compost to fill all of the containers that I want to have.

This holiday season I am going to be collecting those metal popcorn tins from work and family and neighbors to grow carrots. I want to fill them with the best soil possible, but with minimal expense. Does anyone have any ideas and strategies for me? For example, I can dig dirt out of the ground in the backyard for the bottom third or half of these containers and then top them off with homemade compost or bagged soil from HD.

What have you done and what advice can you offer? Do I just need to suck it up and either buy bagged soil or wait until the following year when my composting efforts really begin to turn out product?

See below.

Al

You have said/admitted on more than one occasion that your plants "might not be the biggest/best & yields not as good as they could be" with regard to your containerized plants, but you're satisfied with the results, and I've provided links to that quote in the past, so there is no question about whether I'm imagining things. All that's important is that YOU are satisfied with YOUR results, but satisfaction and the perception of what constitutes a quality growing experience vary widely by individual. The number of people I have helped AVOID the ill-effects of their practice of growing in media based on small particulates (like peat/compost/coir/sand/topsoil) runs into the several thousands just here at GW, which is pretty convincing testimony that ANY soil made primarily of small particulates is fraught with potentially negative issues centering around the effects of excessive water retention and accompanying limitations on the grower's ability to water properly.

Al

I think the take-home message of the little debate going on above is that soil doesn't work very well as potting mix. ;-]

Gardening and container culture are two distinctly different approaches to growing, with container culture being much closer to hydroponics than it is to growing in the earth. Water behaves in containers very differently than it does in the ground; and the most successful and proficient container gardeners recognize and allow for the differences, leaving the practices that work so well in the garden, but prove to be limiting in containers, in the garden.

Compost is a wonderful addition to our gardens and beds, but a poor choice as a significant fraction of container media by virtue of the fact it's excessively water retentive and supports significant volumes of perched water.

Al

We can say with certainty that soils with a high % of fine particulates hold more perched water, so they present more difficulty and a much narrower margin for error.

I think it's important to understand that a few larger particles (perlite or bark pieces, eg) mixed into a water retentive combination of the fine ingredients listed above (peat, compost, coir, sand, topsoil) won't improve drainage or the reduce the ht of the perched water table. The very best you might hope for is a reduction in the o/a volume of water retention, and then only if the ingredient you're amending with isn't internally porous.

To illustrate what I just offered, ask yourself how much perlite it would take to make a quart of pudding drain well & improve it's drainage (flow through rate) and aeration? Do you think 50% perlite would do it? No? 60%? 70%? Now we're getting close. But wait. If we add 75-80% of something like pine bark or perlite to pudding or compost to get it to drain and improve aeration, aren't we then growing in pine bark or perlite AMENDED with compost?

Compost in soils can be made to work well if it's a small fraction of the whole (under 15%) and the rest of the particulates are coarse. From the plant's perspective, grower convenience aside, growing in a soil with any combination of peat, compost, coir, sand, topsoil, or other fine particulates as its primary fraction is going to impose inherent limitations not associated with soils comprised primarily of larger particulates.

It doesn't matter to me what people grow in, and I'm not trying to change the way anyone who doesn't care to change grows; but there are many aspects of soil science so well defined that they can't be misinterpreted, allowing us to draw some very specific conclusions about the cause/effect relationships of certain practices. Hopefully, clarifying some of these cause/effect relationships will help others make the decisions that make their growing experience more rewarding.

Al

If you wanted to keep them as containers I think that the cheapest way to fill them would be to go to a nursery of landscape supply place that sells potting mix in bulk.

You can also mix your own potting soil - there are a number of threads about "Al's mix" (tapla from above) in the Container Gardening forum - it might not be cheaper than bulk mixes but using the recipe and suggestions I think I can make a much better potting soil than I can buy locally premixed.

Your post reminded me of how people grow carrots for shows (I assume mostly in the UK) and guiness records. The link below is a nice blog about one gardener's season. You could also google 'growing carrots in tubes' or 'growing carrots in pipes' for more ideas.

Best of luck!

The ratio listed above can be adjusted to fit your water retention needs by varying the ingredients, but the key to the soil's productivity and to how easy it is to grow in lies in the fact that it is well-aerated and holds little or no perched water, yet still has good water retention ..... it just doesn't hold water in lakes at the bottom of the container like the peat or compost-based soils.

Good point about the raised bed thing. Partially burying your containers or sometimes just setting them on the ground so there is a bridge of soil between the soil in the pot and the ground, turns your container into a mini-raised bed (hydrologically speaking), and employs the earth as a giant wick to help drain the excess (perched) water from the soil in the container. This allows you to grow in soils that would be too water retentive to offer best results if used conventionally.

Don't get me wrong .... I'm not arguing against what someone WANTS to do, do whatever you want - I have no dog in the fight; but perceived results are very subjective. What suits one person fine may not be good enough for the next. I've helped enough people (thousands) rid themselves of the problems associated with water retentive soils to know that a well-aerated and durable soil stands head & shoulders above the soils based on fine particulates.

Al

That may seem like a radical statement, but it's entirely true. All plants have a given degree of genetic potential to grow and produce under perfect conditions. Our job as growers is to eliminate the limiting factors or reduce then to the greatest degree possible. It is only by making conditions perfect that we can optimize growth and vitality. Soils that support significant volumes of perched water (and the soil you described assuredly does - probably 3-4" or more) are limiting if you water profusely (for reasons stated upthread) and they are limiting if you try to water in sips to avoid the effects of soil saturation; this, because of the build-up of dissolved solids from fertilizer salts and tap water that aren't being flushed from the pot when you water + the lack of adequate aeration due to compaction.

As I said, I have no quarrel with whatever someone wishes to grow in, but there are limiting factors assigned by science to soils comprised of fine particulates as their primary fraction.

Al