What's the environmental impact of industrial sources of store-bought bagged soil? Is it a 'net positive' in terms of building soil & storing carbon?

Question

To help grow lots of trees and ecologically friendly gardens, I've bought lots of bags of soil over time. There are better, more local sources of soil/mulch/compost, but nevertheless I go the route of bagged soil sometimes.

As I build soil I wonder about the way the soil is built that I get in bags. Is it storing carbon, or does it have an overall increase in CO2 emissions from the industrial process(es) and sources for bagged soil? I also realize some source materials are better or worse than others ecologically speaking, so it depends on the ingredients - e.g. peat moss harvesting for soil mixes can be worse for ecological health than the benefit of a home garden. Overall I wonder how well the bagged soil is really "building soil"?

An example bagged soil I get is something like this https://www.homedepot.com/p/Kellogg-Garden-Organics-3-cu-ft-Raised-Bed-and-Potting-Mix-Premium-Outdoor-Container-Mix-649/204643152 and similar bagged soil from hardware stores of various sizes.

Answer 1

Advice From the Dirt Doctor

This question is really multiple questions.

1. How well is bagged soil really "building soil"?
2. How is the soil built that I get in bags?
3. Is it storing carbon?
4. Does it increase CO2 emissions from the industrial process?
5. Does it increase CO2 emissions from the sources?

Trying to roll all that into one answer could be quite a challenge.

Bagged soils can vary quite a bit, not only from one product to the next, but also with individual products that change over time as the recipe gets altered. The product you linked to is very similar to many bagged soils which contain mostly wood chips. They do add other things that give it a little boost, but in a very short time you are left with little more than wood chips.

I'm an avid gardener and I never buy that stuff. I use it when my customers insist, but I prefer other methods for building soil. I have many reasons for this. I'll try to focus on the specific reasons that pertain to your question.

Although it's very convenient the cost is enormous. Reflected in the price you pay is the cost (and impact) in getting it to you. Whenever possible, you want to use materials that are close at hand. You say that there are "better, more local sources of soil/mulch/compost" and it seems like you understand the relevant issues there, so let's move on. I don't need to preach to you about that.

Is it storing carbon? That's a trick question. The carbon in wood chips is already stored. It's not permanently sequestered. It's temporarily stored, or held, in the form of carbohydrates that break down and return to the atmosphere. A tiny bit of it gets converted to humus by earthworms and microbes, and that lasts a little longer, but the actual carbon storage is what happens in the plants you grow in that soil. It's helpful to think about your "carbon storage" in terms of how much carbon is looping around in your personal carbon cycle measured by the size of the biomass in the ecosystem you are creating with your trees and gardens.

If permanent carbon storage is one of your goals, then consider using biochar. Ground up charcoal can help build soil structure, and it can assist microbes, but it doesn't break down carbon and return it to the air. It breaks down at a rate that is faster than sand but slower than perlite. Developing soil structure is an important part of building soil.

This gives us an interesting segway into the main problem with your question that will cause problems for anyone trying to answer it. You're using the term "building soil" very loosely. Are you talking about soil structure? Ratio of organic to inorganic substances? Drainage and runoff concerns? Stability of PH? Bioavailability of minerals? Ecosystem for microbes? Resistance to disease? Mineral content? Range of organic compounds? Stability of carbon? Health of mycorrhizal fungi? Interactions between all of the above? I could go on and on (actually kinda did), but these important concerns are all enshrined in the term "building soil". I won't even get started on understanding the "initial conditions" of your existing soil, but that's where I would start before adding anything.

Adding bagged soil in general will help you improve many of those aspects of soil building (but not all), even if it costs a lot and harms the environment. Most of your question seems to be swirling "carbon emissions" and "soil building" around in a giant blender. It's like you're fighting yourself and it's a challenge to weave those together in a coherent way. With that in mind, now would be a good time for me to suggest that you consider how I view the proper goals and ideal solutions regarding your concerns as I see them.

"To help grow lots of trees and ecologically friendly gardens..." (music to any green thumb) the target should be to produce an ecosystem that does not require any inputs at all. In terms of "Sustainable Living" you can do no better. Granted, you may have to add a lot of things at first, whether it be bags, bales, truckloads, or smashed pumpkins. If you do it well, your soil will produce more than it consumes when it's teamed up with all the other multifaceted factors of ecology from the sky above to the wells below.

Answer 2

Bagged soil contains a little bit of decomposed organic matter which is the ONLY thing that improves any and all soils.

Bagged soil is composed of very little actual soil. Lots of inert ingredients. The main boon to bagged potting soil is sterilization. Bagged soil, potting soil is critical for any plants planted in pots. Plants in pots that do not have the advantages of the larger body of garden soil, checks and balances. No disease or insects.

Sterilized potting soil has never been meant to be used in the out of doors garden soil. NOT at all necessary and sorry, not at all a way to improve your garden soil.

It will not HURT your soil but, I encourage you to stop expending all this money for something that can be done for far less money and work. The best and ONLY way to improve any soil from sand to clay...is simply dumping DECOMPOSED organic matter on the top of the soil. DECOMPOSED. If organic matter is not decomposed it should stay in the compost pile or bin until it IS decomposed. Adding extra nitrogen speeds up decomposition because decomposing organisms use NITROGEN for fuel.

Bagged potting soil has a bunch of neutral filler mediums such as: peat moss, vermiculite, pearlite, coir. Sterilized. All plants in pots need sterilized formulated well draining medium, never garden soil.

You need to find a super source for DECOMPOSED organic matter, well aged horse or steer or chicken manure? Well aged. If you are able to see sticks, chunks of old matter that you are able to recognize then that matter is not decomposed. It has to be uniform, a bit larger than grains of soil, lots smaller than non decomposed bark mulches, uniform color, SMELLs wonderful too, be used on top of soil you want to improve THIS YEAR. Dual purpose, this stuff smothers weeds, weed seeds and gives the soil organisms something to eat for fuel and reproduction.

This is so important I am spending a bit more time explaining the importance of decomposed organic matter. (DOM). In any natural soil profile the very top layer is organic matter. Stuff dies and falls to the ground. This in no way has the chemistry plants need to do photosynthesis but it causes the TILTH in the soil plants need to thrive. Plenty of pore space for air, organic matter to buffer any pH problems, organic matter to hold onto water longer while still allowing air to fill the pore spaces in the soil. Organic matter to help hold onto and release more slowly balanced fertilizer and water.

As stuff dies it lands on top of the top most horizon of soil, the 'Top Soil' horizon. It then decomposes as all things once alive will immediately begin to do after death. Those decomposers use NITROGEN for energy nothing else. Decomposers get that nitrogen before any plant roots are able to take advantage. This is just basic soil science. Soil, no matter how dark and friable and yummy looking it is does NOT come with fertilizer. Just doesn't. The reason for this in nature is population control...of plants.

Decomposed organic matter dumped on top of the surface is the best way to improve...any type of soil. Versus rototilling or double digging or adding gravels, gypsum, sand, compost! Freshly added decomposed organic matter summons soil life to come eat me! Soil organisms both macro and micro use DECOMPOSED organic matter for fuel. Not un decomposed organic matter but decomposed organic matter. These organisms come up to the surface to eat this material that is decomposed then they go back into the soil (4 to 6") poop out their dinners and mix decomposed organic matter into the soil PERFECTLY. They aerate at the same time. With this fuel they are able to reproduce and make any soil alive and healthy. Any soil type. Within one season you can make caliche clay into beds with incredible tilth. I dumped decomposed organic matter on my lawn where I wanted to have a new plant bed the next year. The soil was BLUE CLAY. The stuff they use to make porcelain figurines. In 8 months that blue clay was almost completely black. Black streaks of DOM from the soil organisms pooping it out into the soil. The grass I dumped it onto turned into a 'cover crop'. I double dug that bed, made trenches at the bottom and I had the perfect new bed for new plants. Adding a bit of fertilizer and watering always when necessary, esp. for newbie plants. All my plant beds are 'raised' with those trenches at the bottom. I can't imagine doing this any other way no matter the location or the type of soil.

I did manage to get a load of potting soil from some growers dumping their pots out. Put it right on top the ground where I was soon to make my plant beds. Got mixed in sort of kind of and it sort of kind of worked. Didn't help that much but didn't hurt at all.

Fertilizer will always have to be added, judiciously of course! Knowledgeably. No compost will ever replace fertilizer. Period.

Water will always have to be added judiciously and with knowledge.

I always double dig and form my forever plant beds ONE TIME. Trenches at the bottom so the water can collect and with physics that water helps to PULL excess water out of the soil, allowing the pore spaces to fill with air. Those beds change from year to year just by cleaning out the trenches and dumped decomposed organic matter on top of those beds and/or growing a green crop on that bed for the winter. Turn it all over in the spring and in a month after adding a bit of nitrogen, that bed is ready to plant and have some balanced fertilizer added. Caliche Clay first year garden the kind of soil when wet becomes pure mucous. Volcanic pumice I think 2nd or 3rd year, look at the difference in soil from the original in the walkways.
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Quit worrying about carbon. Which is not CO2 anyway. Neither of them cause any harm whatsoever no matter how dumb we humans are! None. CO2 is why we are here. CO2 is why all life on this planet is here. CO2 will never cause global warming until all life and oceans are gone. CO2 is odorless, colorless, NON toxic and very heavy. CO2 gets stored in the soil and in the oceans until the temperature rises a bit releasing the CO2 from storage, or sequestration just in time for plants that need it during the growing season. The ice is not melting, the sea levels are not rising and the polar bears are profoundly happy. We mostly certainly are in a Grand Solar Minimum of global cooling. Just wait until you learn the ramifications you couldn't imagine! But warming? I can tell you quite sincerely and securely there is no global warming happening, has happened nor will happen. Truly an amazing scam...