Mention the words “fish fertilizer” and all too often growers are holding their noses. Sure, some fish-based products stink, but that’s not necessarily a bad thing! An aside—some growers mistakenly believe that root feeding fish-based products to their plants results in their produce tasting fishy! WRONG! But hey, these are probably the same folks that buy those exotically flavored flushing products expecting their tomatoes to taste like mangos! Go figure…
Seriously, there has to be a good reason why fish fertilizer has been used for thousands of years. So we called in organic expert and gardener extraordinaire Jeff Lowenfels to give us the lowdown on the various products available that are derived from our aquatic friends.
American kindergarteners are taught the story of Squanto, a Native American who showed the Plymouth Rock pilgrims how to use fish to fertilize their corn plants. Egyptian children learn about their ancestors using fish to feed plants along the Nile, and Peruvian youths are taught that their pre-Columbian ancestors put a kernel of corn into the mouth of a fish and planted the whole thing.
My Grandfather, an avid gardener and fisherman, was my Squanto. He taught me to bury fish guts and too-bony-to-eat-fish in the rose garden and beneath the tomato plants. The results were outstanding. I’ve been hooked, if you will pardon the pun, on fish as great fertilizer ever since.
What is Fish Fertilizer?
Obviously, fish fertilizer is fertilizer made from fish or fish parts. However, not all fish fertilizers have the same characteristics. In fact, there are actually three different categories of fish fertilizer, so don’t just walk into a store and pick up whatever is on the shelves without doing a bit of homework first.
Each category of fish fertilizer is made using a different process and the products that result, contain varying amounts of nutrients. There are also best uses and special problems, so it is important to know a bit about fish fertilizers before you wade into the water (sorry, I can’t help myself!) and start using them.
In sum, the three categories of fish fertilizers are: fish meals, fish emulsions and fish hydrolysates. Fish meals are made by grinding fish carcasses after a heating process has removed much of the oils. Wastewater left over from making fish meal can be concentrated to produce fish emulsions. Finally, fish digested in vats using enzymes instead of heat produces fish fertilizers called hydrolysates.
The word “fish” can refer to both a single fish or plural when referring to fish in general or to a quantity of fish of the same kind; the word “fishes” is a special kind of plural used to refer to a quantity of various types of fish.
What types of fish are processed into Fish Fertilizer?
Virtually any kind of fish can be made into a fertilizer. However, fish are usually divided into two groups. The first are fish harvested for human consumption. These include tuna, salmon, catfish, halibut, bass, anchovies and sardines. Fish processed specifically to make products for plants and animals make up the second group. These include pollack, menhaden and herring.
What are the advantages of Fish Fertilizer?
Fish fertilizers have several advantages over their chemical counterparts. First, they can be totally organic with all the benefits associated with improved soil structure, increased microbial life and better plant health. Second, fish fertilizers don’t burn plants as readily as chemical fertilizers. Fish fertilizers generally have slower release rates and they don’t need to be applied as often. Moreover, fish fertilizers are not readily leached from the soil, rather they are held in the bodies of the microbes that turn then into plant food. Finally, they often contain trace nutrients not found in chemical formulas.
Characteristics of Fish Fertilizer
The characteristics of a fish fertilizer are based on the way it is processed as well as what is in the fish used. Processing methods are either listed on the label or implied by the name of the kind of fertilizer.
These fish fertilizers are made from whole fresh fish, or fresh fish scraps, which are digested using special enzymes that break down the large proteins in fish meat and bones. Enzymatic digestion is known as hydrolysis, hence the name hydrolysates for the liquid mixtures that result. These liquids are like thick fishy milkshakes. Phosphoric acid is added to the mixtures to halt the digestion process. As a result, the pH of hydrolysates is usually lower than other kinds of fish fertilizers. Also they don’t smell nearly as bad.
Generally, fish hydrolysates have an NPK analysis around 2:3:0, 2:4:1 or 2:5:0. Because no heat is involved in making the fertilizer, and nothing is removed from the fish, hydrolysates contain more of a fish’s proteins, hormones, trace elements and vitamins than do other kinds of fish fertilizers. Application requires dilution to about five or six teaspoons per gallon of water. Fish hydrolysates can be used in all stages of growing.
Finally, unlike the other two kinds of fertilizers, hydrolysates contain all of the fish oils. These oils are excellent beneficial fungal foods, which make fish hydrolysates a good nutrient source for maintaining and increasing soil fungal populations.
Hydrolyzed fish is widely considered to be the “high-end” fish fertilizer product. It doesn’t have a highly objectionable odor like fish emulsion and it’s also highly water-soluble, so it’s great for drippers and foliar applications. It also contains higher levels of phosphorus than fish emulsion products.
Fish is often heated to remove fats and oils to use in various products. The lean carcasses that remain are ground up into a meal and sprayed with phosphoric or sulfuric acid for stabilization and deodorization. Unlike hydrolysates and emulsions, fish meals are not liquid. They have more protein than emulsions, but less than hydrolysates.
Fish meals usually have an NPK analysis around 10:6:2 or 12:6:2. The high nitrogen obviously makes them good for vegetative growth and the relatively high phosphorus content makes fish meals good for root development, too. The down side is that fish meals have a strong odor.
Fish meals are granular or powder in form, and are usually applied at a rate of 5 to 10 pounds per 100 square feet. They continue to smell for a few days and are therefore usually buried into the root zone. They are not recommended for indoor use because of their odor, but if you can stand the smell, they can be mixed into soils where they act as a slow release fertilizer.
Fish meal is a good soil conditioner for use early in the outdoor growing season—it’s ideal in new vegetable or flower beds because it will help root development. Although most fish-meal fertilizers will last for 6-8 months, most of the benefits are realized in the first few months.
After oils, fats and proteins are removed from fish, a liquid slurry is all that remains. This slurry can be concentrated by evaporating up to half of its liquid, resulting in a syrupy emulsion suitable for use as a fertilizer. Some phosphoric acid is added to stabilize and deodorize things. This lowers the pH of the emulsions, which is still not as low as that of hydrolysates.
The cooking segment of the fish emulsion manufacturing process destroys a lot of the fish “goodies” such as the vitamins and hormones so useful to plants and microbes. There is much less protein in emulsions, and fewer solids, but the upside is that fish emulsion is more soluble than other fish fertilizers and cheaper, too.
Fish emulsions have an NPK analysis of 5:2:2 or 5:1:1, even though they are known for their micronutrient content. As the most soluble fish fertilizers, they are good for foliar feeding.
The fish used to make emulsions are usually “trash” fish, which are harvested only for this purpose and not for consumption by humans. They often contain toxics. Menhaden, for example, spend part of their lives in waters that are heavily polluted with metals. Some freshwater fish that can’t be eaten because they are polluted are also often processed into fish emulsions.
Moreover, if the steam employed to strip oils from the fish is from a municipal source, it usually contains chlorine. When the final liquid is concentrated, so is the chlorine—reportedly up to as much as 50%. Chlorine can be harmful to plants and beneficial soil microbes, so you might want to review product MSDS reports to make sure what you buy isn’t too loaded with chlorine.
Application rates of fish emulsions generally run about five or six tablespoons per gallon of water. Fish emulsions are often used in mixtures made up of kelps, other seaweeds and crab shells. They sometimes contain additional materials to raise the NPK. These may not be bad, but you need to take into account what they provide before using these fish fertilizers on your plants.
The nitrogen contained in fish emulsion is released more gradually than in many other non-fish-based fertilizers. Fish themselves naturally contain about 2.3% nitrogen. However, some fish emulsion products contain synthetic sources of nitrogen, such as urea, to boost the nitrogen percentage. Be sure to check with the manufacturer to find out if their fish emulsion product is comprised only of organic inputs.
Common Objections to Fish Fertilizers
There are some basic objections to using fish fertilizers, which may help you decide to use one versus another.
One of the biggest concerns about using some fish fertilizers is their smell. Fish meals, for example, smell horrendously. The odor goes away after a few days but using the stuff inside might be problematic, even for those growers with the largest carbon filters! Fish emulsions can also have a strong, offensive odor even when deodorizing agents are added to them. Generally, hydrolysates have much less, if any, offensive odor.
While humans may take offense to the smells of fish meals and emulsions, many pets and pests find the odor attractive. Cats, dogs and raccoons love to eat fishmeal and some dogs like to roll in it. If you are concerned about animals disturbing your plants, take protective action.
Adding to the problems caused by high concentrations of chlorine in the steam water used to cook some fish fertilizers are the existence of other toxins. Some fish fertilizers contain heavy metals like mercury, which are found in fish living at the top of food chains. Concentrating solutions when making emulsions also concentrates these toxins. However, these fertilizers may still be fine for inedible plants.
Unfortunately, the amount of toxins in a fish fertilizer is not going to be listed on the label. However, you can look up individual fertilizers by—to determine any heavy metal content—on a great website maintained by the Washington State Department of Agriculture.
No one should ever buy fish fertilizer made from endangered or depleted fish stocks and some argue that there are good reasons not to buy any fish fertilizer made from “trash” fish. For the most conscientious growers, only waste fish and fish wastes from human consumed fish are acceptable. Again, a little snooping around on the Internet can provide you with the valuable information needed to make a rational purchasing decision.
In this day and age, there are other sustainability considerations. Packaging, energy resources spent on processing and transportation, as well as additives used are all inputs to making a choice as to which category or brand of fish fertilizer to purchase. Again, a little research is worth it in terms of environmental, plant and human health.
Suitability for hydroponics and foliar applications
Fish emulsions and fish hydrolysates can be used in hydroponics systems because they are liquid in form. Emulsions are more soluble and some of their nutrients are plant useable without beneficial microbiology, but both work best in organic systems with microbes. Odor is a concern, especially with emulsions, and toxins may be as well. If you use a filter in your system, fish hydrolysates may need straining to prevent clogging the filter’s fine mesh screen.
All of the major hydroponics companies sell fish based hydroponics fertilizers. They also supply lots of information to promote them, but read labels carefully and fish (ouch!) for the necessary information to make an informed decision. You can also request MSDS (material safety data sheets) from these companies.
Fish fertilizers as a catalyst for beneficial biology
Organic fish fertilizers excel at supporting the microbe herd that is at the base of the soil food web. They all provide some NPK and most, at least those made from sea fish, also provide trace elements, micronutrients and other good stuff.
Fish hydrolysates, in particular, come about as close to duplicating the practice of burying a whole fish. Only the hydrolysis process makes the fish more available to microbes, breaking down large molecules into tiny ones. Microbes can and do happily feed off the organic matter and proteins from the meat and guts. Calcium from the fish bones is also retained in hydrolysates. And, as noted, the oils in hydrosylates make great fungal food for those plants that prefer fungal dominated soils: perennials, trees and shrubs. For this reason, hydrolysates make great fungal food for compost teas.
Fish meals, too, support loads of microbial activity. They contain tremendous amounts of protein and are great foods for bacteria, and annuals and vegetables that prefer a bacterial dominance in their soil. Covered with bacteria, fishmeal added to a compost pile gets the pile cooking due to its high microbial metabolism. In addition, flies (and their larvae) love it, which in turn attracts other members of the soil food web.
Fish Fertilizers: Be an educated consumer
Not all products sold as fish fertilizers are made just from fish. Some contain non-fish additives as previously mentioned—primarily seaweed and crab shell. The seaweeds are full of micronutrients, auxins and cytokinins; crab shells provide chitin found in the cell walls of fungi. Sometimes, however, non-organic materials are added to boost NPK, so always read the labels on fish fertilizers.
The right fish fertilizers, or combinations thereof, can be great for your plants. Fish hydrolysates provide more nutrients and vitamins, hormones and micronutrients. Fish meals are slower acting, more suitable for outdoor use and larger areas. Fish emulsions are ideal for quick-acting foliar sprays.
However, while fish fertilizers can be extremely useful, do your homework before buying. Research the web, read labels and know what to ask for and you won’t go wrong.
Words: Jeff Lowenfels – author of the best selling gardening book “Teaming With Microbes: The Organic Gardener’s Guide to the Soil Food Web” from Timber Press.
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