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I have several piles of commercial, bagged top soil and potting mix that have been lying in my garage for at least 10 years. I'm doing some renovations and can really use some extra soil for some new garden beds and filling some pots.

Is there such a thing as this soil being past its prime?

It's a typical garage in Central Florida: hot and humid all summer, typically dark, not too cold in the winter.

I'm wondering if I'm working with suboptimal materials trying to make use of this stuff in my garden.

  • Is there something you would like me to add to my answer? – J. Musser Feb 11 '15 at 16:29
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If this is topsoil, not a bagged potting mix, it will contain lots of soil microbes. These can sour the soil if it is stored damp. I've used 14 yr. old bagged soil before, and most of it was fine. I did a smell test. Some of the bags were still damp inside (completely sealed), and a couple of them smelled sour. The others, including what dried, smelled normal (compared with healthy topsoil from my garden) when moistened.

I think of topsoil as living, compared to potting mix, which I think of more as a substrate. Topsoil will slowly decline without maintenance, especially if damp. Dry topsoil will last a long time, but all insect/earthworm life (which may not be present in bagged topsoil anyway) will die, leaving only dormant microbes. Also see this article, which has relevant info.

Dormancy is a reversible state of low metabolic activity that organisms enter when they encounter hard times, such as freezing temperatures or starvation. Unlike plants that follow predictable growth cycles, microbes don't have to follow a linear progression. They could be growing, experience distress and go back to sleep. Once conditions change, they could start growing again without having to go through a full cycle.

If the soil smells fine, I'd use it. You shouldn't run into any problems. If it doesn't smell fine, it may have gone sour. I'd let it breath outdoors in the sun for a while (maybe a month) before use, and possibly get some analysed so I can see what's wrong with it (only if it was some quantity). Otherwise I'd use it in small amounts to fill holes in the lawn, or something like that.

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I'd go a bit simpler than @J. Musser - just set aside an area (where you want it, or on the driveway, or on a tarp on the lawn - depends what you have available for space and how you want to use it) and unbag it. Let it get some air and water, then use it. Anything "bad" that may have happened in the bags will self-revert on exposure to air and water for a week or two, IMHO. Potting mixes with bark materials will have broken down a bit (more humus, less bark chunks - progress by my lights) if they are moist, and it all may be a bit dusty if it's dried out, but that should be fine.

If an excessively well-sealed bag has gone anaerobic and "soured" the anaerobes will die in the face of air exposure and aerobic bacterial will take over again.

To have an excess of caution, I'd let it air out (spread 6-8 inches or less thick) for a day or two and then toss some finished, more recent compost on there and stir it about, as a "good bacteria source." Hose it a bit if the rain doesn't do the job. Then get something growing in it (even if just a cover crop) to really reintegrate it to the land of living soils.

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