How Green Is Your Organic Soil Amendment?

This is a guest post from Rachel of Dog Island Farm. Rachel and her husband Tom intensively urban farm a quarter acre parcel in the San Francisco Bay area. They are pretty famous in the urban homesteader world for going a year without stepping foot in a grocery store and providing no-nonsense advice on urban backyard farming. Dog Island Farm boasts goats, bees, rabbits, chickens, turkeys, fruit trees, perennial edibles and a large organic vegetable garden.

Dog Island Farm

Dog Island Farm, where Rachel and Tom urban farm.

In this guest post, Rachel shares what she’s learned about various organic soil amendments. I learned a lot and I hope you will too.

There are a lot of different types of organic soil amendments. Here, I’m breaking down some of the more common and less common ones, what they are used for and where they come from. Some are not exactly environmentally friendly. While researching all these different amendments I was surprised at how many were unsustainable, nonrenewable, or involved open pit mining to obtain.

Another consideration is that many common organic soil amendments and fertilizer components are by-products of industrial meat production. I’d rather see bone, feather and blood meal used in gardening than wasted or turned back  into food for other industrially raised animals, but vegetarian and vegan gardeners should be aware of the amendments that are animal-derived.

Soil Amendment

Alfalfa Meal – Balanced fertilizer that contains moderate amounts of nitrogen, phosphorus and potassium but also includes trace minerals. Is good for adding organic matter to the soil. As the name suggests, it’s made from alfalfa. May be of concern now that GM alfalfa has been approved. Could introduce glysophate into your soil.
Green Grade: B- for risk of contamination. Tips: Seek out meal from non-GMO alfalfa.

Azomite – Slow release fertilizer of trace minerals. It’s open-pit mined from ancient deposits of aluminum silicate and marine minerals in Utah. It is a nonrenewable product.
Green Grade: C for non-renewability.

Bat Guano – Fast acting fertilizer with high amounts of nitrogen and phosphorus and a smaller amount of potassium. It’s the accumulated manure of bats which is then mined. Bat colonies are particularly sensitive to the disturbance of mining and, unless bat guano harvesting is done very carefully, guano mining can lead to total loss of bat species.
Green Grade: D for ecological disruption.

Blood Meal – High nitrogen fertilizer made from the blood of animals, which is a waste product of the meat industry. Water soluble so it can be used a foliar feeding. We don’t use it primarily because I can’t keep my dog out of it.
Green Grade: B+ for renewability. Vegan Grade: F for dependance on industrial animal production.

Bone Meal – Slow release, high Phosphorus fertilizer with some nitrogen made from the bones of animals, which is a waste product of the meat industry. It is also a good source of calcium.
Green Grade: B+ for renewability. Vegan Grade: F for dependance on industrial animal production.

Compost – Plant material that’s been broken down by microbes. It can have a variety of nutrient profiles depending on what plant materials were put in it to create it. Currently homemade compost is the safest to use as persistent herbicides and pesticides are being found in commercial compost. Some commercial composts are made using biosolids (sewage sludge) and these may present a risk of residual medications or harmful bacteria.
Green Grade: A for home produced compost. B-D for industrially-produced compost depending on quality and source material and risk of contamination with persistent chemicals, biosolids, and noxious weed seeds.

Cottonseed Meal – Slow release fertilizer containing mostly nitrogen, moderate amounts of phosphorus and small amounts of potassium. It is acidic so it works well for acid loving plants. May be of concern considering a lot of cotton is GM. Could introduce glysophate into your soil.
Green Grade: B- to C for risk of persistent herbicide contamination.

Dolomite – High magnesium and calcium amendment that is used for raising the pH of acidic soils. It is calcium magnesium carbonate and should only be used on acidic soils that are deficient in magnesium. Open pit mined and nonrenewable, but deposits are common around the world.
Green Grade: B.

Feather Meal – Slow release high nitrogen fertilizer made from feathers, which is a by-product of the poultry industry.
Green Grade: B+ for renewability. Vegan Grade: F for dependance on industrial animal production.

Fish Emulsion – Moderate nitrogen with some phosphorus and potassium. Is good for foliar feeding. It’s a by-product of the fish oil and fish meal industries. It’s really stinky and another fertilizer I can’t keep the dog out of.
Green Grade: C for renewability; many fish stocks are threatened. Vegan Grade: F for dependance on industrial animal production.

Green Manure – A cover crop that is turned into the soil before it goes to seed. It adds organic matter to the soil and can be used for weed suppression. Legume green manures can add nitrogen to the soil, and very deep rooted green manures can mine the subsoil for trace minerals. Many green manures, however, will add few additional nutrients to the soil. Best results will come from careful understanding what the gardener is trying to achieve with the green manure (biomass, nitrogen boost, soil tilth, etc.) and choosing the appropriate green manure for the job.
Green Grade: A.

Greensand – Slow release high potassium fertilizer which also contains trace minerals. Good soil conditioner. It is open pit mined from 70-80 million year old marine deposits and is nonrenewable. Primarily produced in New Jersey.
Green Grade: B- for non-renewability.

Gypsum – Fast release calcium and sulfur. It also acts as soil conditioner improving compacted and heavy soils. Open pit mined and nonrenewable, but deposits are common around the world.
Green Grade: B+.

Humic Acid/Humates – Not a fertilizer but helps aids plants in the absorption of minerals and nutrients. Open pit mined and nonrenewable.
Green Grade: B.

Kelp Meal – Good potassium and micronutrient source that also aids in increasing microbial activity. Obtained from dried seaweed. Kelp grows quite fast, so it’s a bit like the bamboo of the ocean. With good stewardship, a renewable resource.
Green Grade: B+.

Manure – Various animal manures contain different profiles depending on the animal they came from. They contain trace minerals and nutrients along with NPK. By-product of the livestock industry. Animal manure may present a risk of residual medications, including deworming medication, harmful pathogens and may contain weed seeds. Hot industrial composting tends to mitigate these risks but it does not remove all medications used, in particular arsenic which is a concern especially for poultry manure. Most animal manure is best used composted.
Green Grade: A-C depending on quality and source material and risk of contamination with persistent chemicals, biosolids, and noxious weed seeds. Vegan Grade: C to F depending on production methods for dependance on animal production.

Oyster Shell Lime – Amendment made from oyster shells that helps condition soil, provides calcium and trace minerals and increases the pH of acidic soils. Fine grade powder is faster acting than rough crushed shells.  Byproduct of commercial oyster farming beds, which are typically well managed and renewable.
Green Grade: B+ . Vegan Grade: F for dependance on animal production.

Peat/Sphagnum Moss – Soil and potting mix amendment that aerates, helps with water retention and helps lower pH for alkaline soils. Unfortunately it is mined from very fragile ecosystems that can take thousands of years to reestablish themselves. While technically renewable, peat bogs are mined far more quickly that they can renew, and unique flora and fauna are greatly disturbed in the process. Primarily imported from Canada.
Green Grade: D, for habitat disruption and functional non-renewability of the resource.

Rock Dust – Mined minerals that provide trace minerals to soil. Mineral profile varies based on what rocks make up the dust. Granite-based dusts very slowly increase pH of acid soil. Often a by product of other horticultural or landscaping projects. Often rock dusts are made from mixed glacial till. Typically the source rock must be open pit mined, and transportation costs are often high for this heavy product, but deposits of rocks are pretty inexhaustible.
Green Grade: B+

Seabird Guano – Fast acting fertilizer with high amounts of nitrogen and phosphorus and a smaller amount of potassium. It’s the accumulated manure of seabirds which is then mined. Mining can disturb seabird colonies. Primarily produced in Peru.
Green Grade: C – for ecological disruption.

Sulfate of Potash – Very high fast release source of potassium. Also includes sulfur. Open pit mined product. Nonrenewable. Primarily mined in New Mexico.
Green Grade: C+ for non-renewability.

SulPoMag – Also known as langbeinite. Good source of sulfur, potassium and magnesium. Mined underground from an ancient seabed. Nonrenewable. Primarily mined in New Mexico.
Green Grade: C+ for non-renewability.

Worm Castings – Water soluble fertilizer with lots of nutrients, trace minerals, microbes, and enzymes. Produced from the droppings of worms. Infinitely renewable, good way to convert kitchen scraps and waste paper into high-quality fertilizer, strong evidence that plants grown with incorporated worm castings are better able to resist disease pathogens.
Green Grade: A+ for home prepared, A for commercially prepared. Vegan Grade: F for dependence on animals.

Learn more about Rachel, Tom and Dog Island Farm

About Dog Island Farm.

A Year Without Groceries on

Rachel and Tom interviewed for Thrive by Whole Foods:



    • says

      Mercury can be a concern. If you eat the fruit of the plant, you are much safer as the fruit generally isn’t contaminated by heavy metals. Same is true for lead as well. In regards to mercury specifically, the roots appear to be the most contaminated by mercury and it is possible that the roots are a barrier to mercury entering the leaves and stems of plants as these generally have little to no contamination from soil borne mercury. The do, however, absorb atmospheric mercury, but that is unrelated to the mercury in fish emulsion.

  1. says

    I think some of the mind materials might get lower than a B in my book. We have some green sand mining here in Texas, too.

    I’m glad someone wrote this up, I’d thought about it a year ago when I was hearing about some organic alternatives that aren’t necessarily very environmentally friendly either.

  2. Austin says

    Very, very interesting, thank you! Feeling very good about my compost pile just now…
    (It does seem a little weird to me that Worm Castings get a Vegan grade “F”, though, when eating kitchen scraps is what worms want to be doing anyway.)

    • Greg says

      Some vegans dont eat honey either because its enslaving bees or something like that? I guess every one has to draw a line in the sand somewhere.

      • says

        Greg is correct. Many vegans consider *any* use of animal products to be unacceptable. You’re keeping worms from living in their natural habitat, so therefore they are being enslaved so that you can harvest their feces.

    • V says

      I would think worm castings should have a rating more like “B-F”, depending on the source. Some commercial operations will harvest in a way that kills many/most of the worms. However, some setups (including most home-scale worm composting) can avoid most/all of the worm death with proper management – I expect that many vegans would find this acceptable. In climates where the worms are native or naturalized (such as California), this is even easier.

  3. says

    I use Biogrow 365 and wonder how it stacks up. I would love your input: or read:

    What is in Biogrow365?
    Biogrow365 is an all purpose liquid organic fertilizer and microbial inoculant all in one. It is derived from naturally occurring source material including organic poultry manure and a select range of microbes formulated to strengthen sustainability in soils through mineralization and elemental conversion. A biological environmentally sustainable natural solution.

    I figured I was doing a good job of sourcing an organic fertilizer.

    • says

      It’s pretty ambiguous about what is in it other than “organic poultry manure” so it’s hard to comment on how safe it really is. I will say this though: Organic poultry manure does not necessarily mean that the poultry manure came from an organic poultry operation. All poultry manure is considered “organic” for crop production. It’s a slight of hand really.

  4. says

    A note on manure and composts that include manure: here in Washington we’ve had a few reports of persistent herbicides showing up in manure because the source animals grazed on fields that were sprayed. Once it’s in your garden soil there’s not much you can do but remove all of it. Read more here:

    Also a note on biosolids/sewage sludge: this is often included in municipal compost which is marketed as a great for gardens. Muni compost that is certified will be properly hot-composted to kill pathogens but there is potentially more than just residual medications left in the material. The EPA has done a few national surveys of sewage sludge and found harmful components in every sample. Metals, fire retardants, antibiotics, various prescription drugs, steroids, and hormones. Read more here:

  5. says

    I’m wondering if you have any concerns regarding the use of kelp harvested after Fukushima? It seems to me that there is a high likelihood of radiation contamination in the kelp, which would add radiation to your soil at a faster rate than it will accumulate due to weather patterns and such.

    • says

      Nope, I have no concerns about radiation from Fukushima. Most of the articles about OMG!TheWestCoastIsBeingBlastedByCancerCausingRadiationAndWe’reAllGoingToDie!!!! are completely sensational and don’t really have any basis in scientific reality.

  6. Carolyne Thrasher says

    I didn’t see anything about coir. Did I miss it? If not, what would the rating be for it? I’m getting ready to make some seed starting mix and was planning to use it and worm castings primarily. Not sure what to replace the vermiculite with.

  7. Elena Sopoci says

    Wow! This was a great overview; really appreciate the thoroughness, as well as the consideration of “green” + animal sourced. Thanks so much!

  8. says

    Thank you so much for this post. I have vaguely thought about the eco-factor of my soil amendments before, but didn’t get far beyond “Oh God, I really need to do a better job of composting.” This is incredibly helpful!

  9. Sue says

    Yes, I’d like to know about coir also.
    I’ve worked to not use any peat and to try my best to make good choices, it’s not easy. I think I’m still learning, too. Plus, budget, time, and local availability all come into play. Like everything else, it’s a balancing act.

  10. Karen says

    Just a little comment about biosolids. Whatever you think about chemicals being in it, all biosolids products available to the public must meet Class A standards, which requires them to be pathogen-free and are tested to prove it. The laws around biosolids are pretty stiff. Biosolids are WAY more regulated than animal manures are (for all kinds of constituents, not just pathogens).

  11. Ellisa says

    I live about 1/4 mile away from a cotton field and I doubt I will ever use cottonseed meal on my garden. The chemicals used at harvest time are almost horrific. You can smell the defoliant at our house for almost a week after they spray. My husband kept asking if the exterminator had been by because he kept forgetting that he could smell the cotton field.

  12. Ashley says

    A note on kelp –

    I’m currently going through the master gardener training program, and it’s been drilled into us trainees that kelp forests are the “old growth forests of the sea”, and not quite as renewable a resource as one would think. They provide habitat for lots of critters, and over-harvesting can be very detrimental. I’m sure a lot of this depends on harvesting methods and maybe there are some brands that are more responsible about this, but just some food for thought…

    Also, current research is showing that there’s very little benefit to using kelp as an overall fertilizer anyways, so in most cases it’s not worth the expense. Yes, it can stimulate rooting, but there are other more sustainable compounds that will do the same thing. This surprised me, since I’ve always heard of its benefits. Perhaps that’s the result of marketing?

    Disclaimer: I have not read these studies myself, just passing along the findings of extension specialists based on peer-reviewed research :)

  13. says

    Thank you for addressing the issue of livestock manures and the contaminates that can be found we have worked hard to bring awareness to this issue that all manure is not good for the garden soil. We produce a “clean” manure at Haven Brand that is from our grass fed livestock, harvested, processed and eco packaged by hand as it has been for generations.


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