This subject has been covered hundreds of times with lots of nays and yays. If you use the search function for this forum and enter the search words reuse soil, you'll come up with enough reading to keep you busy for a good long time.

Al

I have planted my third crop in 5 gal. buckets with satisfactory results for an old man, and am already planning my winter planting just as soon as the present crop is finished. I haven't used any soil at all, as I am using composted oak leaves and lawn grass clippings composted with them. I am adding 20-20-20 mixed in water and 10-10-10 guano mixed into the soil before planting. My planting of collards, mustard, and turnips last winter was a great success, and I'm still using the same compost I started with three years ago and will use again this fall for my fall greens. Each bucket holds 4 gal. of soil so I just take out the top 3 gals. mix as I clean unwanted roots out and mix in guano and a little more compost soil if needed. then I'm ready for new plants to enjoy all winter long.

I've posted this several times before:

In my estimation, the only case to be made for reusing container soils is one of economics, and you'll never find me argue against making that decision. If you can't afford, you can't afford it. That said and setting economics aside, you might decide to reuse soil for reasons other than economical. Perhaps the effort involved with acquiring (or making your own) soil is something you might not wish to go through or be bothered with.
In any case, it would be difficult to show that soils in a more advanced state of structural collapse can somehow be preferred to a soil that can be counted on to maintain its structure for the entire growth cycle. So, if the economic aspect is set aside, at some point you must decide that "my used soil is good enough" and that you're willing to accept whatever the results of that decision are.

All soils are not created equal. The soils I grow in are usually pine bark based & collapse structurally at a much slower rate that peat based soils, yet I usually choose to turn them into the garden or give them over to a compost pile where they serve a better purpose than as a container soil after a year of service. Some plantings (like woody materials and some perennials) do pretty well the second year in the same bark-based soil, and with careful watering, I'm usually able to get them through a third year w/o root issues.

Watering habits are an extremely important part of container gardening. Well structured soils that drain well are much more forgiving and certainly favor success on the part of the more inexperienced gardeners. As soils age, water retention increases and growing becomes increasingly difficult. If your (anyone's) excellence in watering skills allows you to grow in an aging medium, or if your decision that "good enough" is good enough for you, then it's (your decision) is good enough for me, too.

The phrases "it works for me" or "I've done it this way for years w/o problems" is often offered up as good reason to continue the status quo, but there's not much substance there.

I'm being called away now, but I'll leave with something I offered in reply on a recent thread:
"... First, plants really aren't particular about what soil is made of. As long as you're willing to stand over your plant & water every 10 minutes, you can grow most plants perfectly well in a bucket of marbles. Mix a little of the proper fertilizers in the water & you're good to go. The plant has all it needs - water, nutrients, air in the root zone, and something to hold it in place. So, if we can grow in marbles, how can a soil fail?

Our growing skills fail us more often than our soils fail. We often lack the experience or knowledge to recognize the shortcomings of our soils and to adjust for them. The lower our experience/knowledge levels are, the more nearly perfect should be the soils we grow in, but this is a catch 22 situation because hidden in the inexperience is the inability to even recognize differences between good and bad soil(s).

Container soils fail when their structure fails. When we select soils with components that break down quickly or that are so small they find their way into and clog macro-pores, we begin our growing attempts under a handicap. I see anecdotes about reusing soils, even recommendations to do it all over these forums. I don't argue with the practice, but I (very) rarely do it, even when growing flowery annuals, meant only for a single season.

Soils don't break down at an even rate. If you assign a soil a life of two years and imagine that the soil goes from perfect to unusable in that time, it's likely it would be fine for the first year, lose about 25% of its suitability in the first half of the second year, and lose the other 75% in the last half of the second year. This is an approximation & is only meant to illustrate the exponential rate at which soils collapse. Soils that are suitable for only a growing season show a similar rate of decline, but at an accelerated rate. When a used soil is mixed with fresh soil after a growing season, the old soil particles are in or about to begin a period of accelerated decay. I choose to turn them into the garden or they find their way to a compost pile.

Unless the reasons are economical, I find it difficult to imagine why anyone would add garden soils to container soils. It destroys aeration and usually causes soils to retain too much water for too long. Sand (unless approaching the size of BB's), has the same effect. I don't use compost in soils because of the negative effect on aeration/drainage. The small amount of micro-nutrients provided by compost can be more efficiently added, organically or inorganically, via other vehicles.

To boil this all down, a container soil fails when the inverse relationship between aeration/drainage goes awry. When aeration is reduced, soggy soil is the result, and trouble is in the making."

Al

Al, thanks for the re-porting of the explanation. I read it when I first came to GW 3 years ago and I didn't understand what you were talking about then :-(

Now, after 3 years being more "serious" at gardening, your discussion becomes so CLEAR, i.e. I know exactly what you meant!

But, I have found that used soil in my containers "looks and feels" good to my eyes and touch - I meant to say it's loose, dark, etc.... - I did re-use it to make new containers. However I normally mix in new soil and amendments.

Is the "look & feel" deceiving? The soil I'm talking about here contains no "barks", just soil and composted cow manure or rice husks, etc. Should I just dump the whole thing into the garden beds? Maybe I should, huh?

Thank you again for taking time answering our newbies' questions.

Xuan (from 'Nam)