Brewers spent grain as a soil amendment


I searched on the site and I kind find anything.
I’m right now spreading about 1 inch of spend grain on top of the
soil and then turning it in to The Claw cultivator tool.
What I’d like to know is how much can I amend the soil with this
material? Is adding this much enough or is it possible to add more?
I am also using coffee chaff and coffee grounds partly as an additive and partly for mulch. Are there any limitations to using this?
Composted cow manure will go on the top of the mixed soil and then the coffee chaff and ground up deciduous tree leaves will go on top of that.
Is this okay?


Brewers Spent Grain as a Soil Amendment

Thank you for this very interesting question that you have posed to the Toronto Master Gardeners. I had never heard of using Brewers Spent Grain as a soil amendment. If I am correct, your plan is to amend your soil in four layers. The first is the brewers spent grain. On top of that you plan to add coffee chaff and coffee grounds. You will then add a layer of composted cow manure on the top of the mixed soil. Finally, you are planning on adding ground up deciduous tree leaves.

Your question is how much of each layer you should be using. The answer is complicated, but to get to your question first, the general idea is to not increase the height of your soil by more than 3″-4”. Secondly, it is preferable to add compost as a mulch rather than digging in additives directly in your soil. For more information on this, please read this posting on the Toronto Master Gardener ASK line: amending depleted soil

My strong suggestion is that you first compost the brewers spent grain, the coffee chaff and coffee grounds, and the deciduous tree leaves before you put them on your soil. Each of these additives, if not composted first, can be problematic if directly added to your soil. If you create a good compost pile now, you will have a very rich and safe compost to add to your garden as a mulch in the late spring or early summer next year.

It is most impressive that you are planning on using soil amendments made from recycled products which industry considers as waste and that often end up in landfills. Do you live close to a micro-brewery or coffee shop where you can obtain these products?

I am presuming you have decided that your soil is very depleted so it needs the addition of this much organic matter. However, you have not mentioned some important details, such as where you are located, the kind of soil you have (clay, loam or sandy), your annual rainfall (to determine how much leaching of nutrients you may have), how big the area is that you are planning on amending, or what you plan to grow in the amended garden bed. What you plan to grow is important so that you make sure that the pH of your soil is right for your plants.

You have also not mentioned whether you have taken a soil test that has led you to believe that your soil is depleted. May I suggest that before you proceed, you get a soil test done? A complete soil test will tell you your soil pH, and give a textural analysis including useful information about water holding capacity and a variety of chemical analyses. The ideal soil pH for most plants is 6.8. Soil tests will also help guide your attempt to modify your soil. However, the biology of soils is not easily or routinely analyzed through soils tests. As a general guideline, ideal soils, from a fertility standpoint, are generally defined as containing no more than 5% organic matter by weight or 10% by volume.

For those like me who did not know about this, Brewer’s Spent Grain is the industrial moniker used to describe the malt after a brewery has already used it to make beer. Malt is generally made from barley that has been soaked, sprouted, and dried. The grain is deemed “spent” because it cannot be used to make more beer, as most of its starches have been extracted by the brewery to provide fermentable sugars to the yeast. This off-shoot of the beer industry is now being used (after processing) as an additive in some “health” breads, and it is being used in agriculture for large-scale soil amendment.

Adding brewers spent grain directly to your soil will potentially lead to an imbalance in your soil. This additive is very high in nitrogen and can burn plants without composting first. It can also be very stinky if it has started to decompose! It would be much better to compost it first.

The addition of coffee chaff and coffee grounds is also a good idea—but again, it would be good to add this additive to your compost pile rather than directly on the soil. Quantities seem important. Using coffee grounds at 10 to 20 percent of the total compost volume has been reported as optimal for compost quality and effectiveness, while over 30 percent can be detrimental.  Be careful not to use too many coffee grounds or pile them up. The small particles can lock together, creating a water-resistant barrier. Also keep in mind what you are planning on growing. The plants that like coffee grounds include roses, blueberries, azaleas, carrots, radishes, rhododendrons, hydrangeas, cabbage, lilies, and hollies. These are all acid-loving plants that grow best in acidic soil. You’ll want to avoid using coffee grounds on plants like tomatoes, clovers, and alfalfa. One 2016 research study found that using spent coffee grounds in growing broccoli, leek, radish, viola, and sunflower resulted in poorer growth in all soil types, with or without additional fertilizer.

There is also a growing body of research that says that digging in amendments can be destructive of the soil structure and the life in the soil. Adding amendments usually involves digging in, roto-tilling, soil turning with a spade, or some kind of incorporation process. You mention using a claw cultivating tool, which is not too bad. However, any cultivation destroys soil structure and a good part of the soil food web. Beneficial nematodes are highly sensitive to tillage and many are killed by tillage, often perturbing the entire soil food web in a disturbed soil.

Therefore in conclusion, may I respectfully suggest to you that you use the additives in your compost pile, and use your compost as a mulch for your garden next year.

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September 30, 2021