There are many organic fertilizer products available online.
Many are not particularly good (potentially even harmful), so I thought I'd browse through and make a list of the best organic fertilizer options for you.
Update: The Organic Fertilizers I Use
I originally focused on fertilizers sold at Amazon.com, but have since stopped supporting Amazon, so I'm now in the process of removing those links.
Instead, I decided to keep the same list, but link to my other favorite online fertilizer suppliers.
And then almost 3 years after I wrote this post, I decided to sell a small selection of the best organic fertilizers I've personally used.
So sometimes I link to them down below, and sometimes I link to other ethical suppliers.
You can check all of mine out here if you're interested (for some of them, I actually tell you how to make them yourself).
This research process involved going back to the fertilizer manufacturers' websites and reading through their MSDS sheets and labels to see what the products are really made of. Lots of work, so I hope it's useful to you.
Amazon sells a lot of fertilizers. I found a few good ones for you, along with some not so good ones to stay away from.
By the way, there are some companies who seem to have their hearts in the right place, but I just can't recommend them because I don't like some of the organic fertilizer ingredients they're blending together. I'm not trying to pick on them, though.
Best Organic Fertilizers
SCD Bio Ag (Similar To EM)
This is basically effective microorganisms, a microbial inoculant. It's not technically a fertilizer, but it's the number 1 product I use in my garden, even before organic fertilizers. Actually, I buy a mother culture, which I can activate to make my own, whereas this is more of an already-activated product that would just be used straight from the bottle. Ignore the lukewarm reviews on Amazon - this product is incredibly useful.
Neptune's Harvest Organic Fish Fertilizer 16 0z
Good price and a really nice liquid fish hydrolysate. I've actually partially moved away from fish products in favor of ocean water products, because the results can be incredible and ocean water is much more sustainable.
Basalt Rock Dust
This is a decent rock dust fertilizer, one of the best organic fertilizers on Amazon, providing a broad spectrum of minerals for your soil instead of just N-P-K. If you can find it locally in your local farm supply store, you'll get a better deal.
Dr. Earth Organic 5 Tomato Vegetable Herb Fertilizer, 12-Pound
This organic fertilizer for vegetables contains fish bone meal, kelp meal, feather meal, alfalfa meal (alfalfa is now genetically modified, but according to the label, this product doesn't contain GMOs), fish meal, soft rock phosphate, mined potassium sulfate, seaweed extract, humic acid, and 7 strains of soil microbes plus endo and ectomycorrhizae. I usually stay away from blends, but these ingredients should be okay. I like that it doesn't contain bone meal and GMOs.
Wholesome Sweeteners - Organic Molasses Unsulphured - 32 oz.
Molasses is an incredible fertilizer! It supplies carbohydrates to feed the beneficial microorganisms in the soil, plus vitamins and minerals. Blackstrap molasses is the best, and you want to go with unsulphured, because the sulfur kills microbes.
1 Lb TeraVita Humic Acid Soluble Powder
This is a little more advanced, but humic acid is an excellent addition to a foliar fertilizer such as kelp or fish because it helps the plant take in the nutrients from those fertilizers. Actually, humates have a number of benefits. This product is the best one I've found, so I was excited when it made it to Amazon.com, but I don't recommend it as a top priority for most home gardeners.
Foli-Cal Liquid Calcium
Most gardens would benefit from the occasional liquid calcium application. I don't generally recommend single-mineral applications without a soil test, but calcium is the exception. There are better liquid calcium products out there, but they are very difficult to track down - this is the best one I found on Amazon and it is decent.
Mycorrrhizal Fungi Inoculant
This is my top selling product, and definitely 1 of the top 3 I recommend to my students, customers and clients. It's a special fungus that associates with over 90% of plant species at the root level and brings those plants nutrients and water, in addition to protecting their roots from predators.
These Could Be Okay
Neptune's Harvest Organic Seaweed Plant Food, 32-Ounce
This is a nice seaweed product from a company that's been around for awhile. Their organic kelp meal is also good. Seaweed is full of natural plant growth hormones and over 70 minerals that improve plant health. Kelp is one of the best organic fertilizer options.
Bioform Liquid Organic Fertilizer 32oz.
This liquid organic fertilizer contains some good ingredients - molasses, seaweed and fish hydrolysate - but it also contains bone meal, which I no longer recommend due to the potential transmission of prions associated with mad cow disease and also heavy metal concerns. I'm always kind of on the fence about bone meal, not wanting to totally bash it, but not promoting it either because of the potential problems and because there are better options.
Mastergardening Liquid Fish Emulsion 16-Ounce Concentrated Organic Fertilizer
This might be okay, but I can't find any information on it, which always makes me walk away. Is it really organic? Is it poor quality? An emulsion is often not as good as a hydrolysate, but can certainly be useful - still, there's no way to tell what is in here because they don't have any info on it.
Dynamite Natural and Organic Mater Magic Plant Food
Seems like it might be okay, but I can't find the ingredients on their website. If they don't list the ingredients, I don't buy.
Jobe's Organic All Purpose Granular Fertilizer 4-Pound Bag
The company looks cool, but I'm not a huge fan of the ingredients in their products. This product (and others from this same brand) contains ingredients that I don't usually recommend - bone meal, sulfate of potash (useful only if you need both sulfur and potassium, which you very well may not), composted poultry manure (may be okay if it was from organic birds, but is it?), and feather meal (which may or may not be okay, depending on source).
Not As Good
Lilly Miller Alaska Fish Emulsion Fertilizers
In my opinion, this organic gardening fertilizer is not as good as some other fish products, and I don't like the track record of the parent company Lilly Miller. I prefer the Neptune's Harvest fish and seaweed up above. That being said, their 5-1-1 product is OMRI Listed, so it's allowed in organic farming. I'm sure it's still beneficial. Update: My fish fertilizer here is way better.
Fish & Poop Liquid Fertilizer-1 Gallon
It's liquid fish and bat guano. Can't find much info on it, and it just doesn't look very good. It may be fine, but I can't find more details on what's in it along with an MSDS.
Miracle-Gro 1001501 All Purpose Liquid Plant Food Jug, 32-Ounce
I don't support Miracle-Gro (made by Scotts - see below). Other than that, this product - fermented sugar beet molasses - could actually be a helpful organic fertilizer and biostimulant in the garden, but my main concern is that sugar beets are now being genetically modified.
These Are Not Recommended
Milorganite Organic Nitrogen Fertilizer, 36-Pound
It's sewage sludge, which research shows is toxic stuff no matter what they do to clean it up. It's true that we need to find ways to deal with our sewage - and more important, we need to stop dumping chemical fertilizers, pesticides, heavy metals and other industrial toxins into our soil and water systems - and using microbes as part of that process is great, but in my view, putting it on our gardens is not the answer.
Scotts Organic Lawn Fertilizer
I don't buy anything from Scotts, not even organic garden fertilizers. In my view, their goal is only profits, not quality. In my view, their chemicals are destroying this earth and they are an unethical company. Just my opinion.
Bradfield Luscious Lawn Organic Fertilizer
Corn gluten can be useful, but this (like most) will contain genetically-modified corn gluten, which we don't want in our gardens because we just aren't quite sure what might happen to it when it gets into the environment and is consumed by microbes.
Do you have any thoughts or questions on which are the best organic fertilizers for your garden? Feel free to let me know below.