There has been a lot of chatter on the net recently about the magical benefits of milk as fertilizer in the garden. Most of the Magic is Imagined.
Is Milk a Good Fertilizer?
The idea of using milk as a fertilizer was started around the year 2000 when a steel industry executive turned dairyman by the name of Dave Wetzel started spreading his excess milk on agricultural land. There have now been several studies looking at this and they have all concluded that milk adds very little value and has no significant effect on plant growth. You can read the full story about how this myth started in How the Myth of Milk Fertilizer Started.
Is Milk Good for Plants?
Most of the information on the internet about the benefits of milk in soil say the same thing so I will use one source to keep it simple. The following quotes are from a Mother Earth News post called Milk as Soil Food.
“amino acids, proteins, enzymes and natural sugars that make milk a food for humans and animals are the same ingredients in nurturing healthy communities of microbes, fungi and beneficial bacteria in your compost and garden soil”
Absolutely true. Microbes will degrade the larger molecules in milk into basic nutrients which plants can then use as a food source. However, the same statement can be made about every living material; fruits, vegetables, plant waste, manure, compost, wood chips and even paper. All living or dead material that was recently living will do exactly the same thing for your garden.
The problem with milk is that it mostly water and the small remaining amount of beneficial organic matter has very little impact on soil, microbes or plants.
Heat Treated Milk is BAD!
“Raw milk is the best, as it hasn’t been exposed to heat that alters the components in milk”
The author clearly does not understand what happens once microbes work on the milk. They break the large molecules down into simple nutrients like nitrogen, and phosphate. Heat would actually speed up the process. Your organic source could be raw milk, heated milk or even cheese–it is all the same thing as far as your microbes and plants are concerned.
Ancient Times
“Using milk on crops and soils is another ancient technique”
I can’t honestly argue against this statement from a scientific point of view, but does it seem likely to be true? Would people in ancient times, when resources were low and famines were frequent, dump good milk on the fields in the hope of a bigger crop? I kind of doubt it.
The ancient Greeks used it to feed animals and to make cheese.
Milk Reduces Powdery Mildew
There is some scientific evidence that milk does keep fungal spores of powdery mildew from germinating. However, it does not stop an existing infection so it does not cure the problem.
Sugars Poison Insects
“Milk sugars are a poison to soft bodied insects as they do not have a pancreas to process the sugars”
I can’t comment on the science behind this statement–need more time to research it. Does the statement make sense? All plants and animals contain sugars–they are vital for life. Insects eat plants and they eat other insects and larger animals. So we know they ingest sugars all the time and their bodies are able to handle the sugars in their diet. So either the sugars in milk are vastly different than sugars from other sources, or this statement is not true.
If soft-bodied insects can’t eat sugar than sugarcane would be free of aphids! A quick look on the net will show you examples of the sugarcane aphid–clearly it is not poisoned by sugars.
The “no pancreas” part may be true, but I doubt sugars are poisonous to soft-bodied insects.
Milk Fertilizer
“For the home gardener, the ratio can range from 100% milk to a 20% mixture with water, with no loss of benefits”.
Milk will act like a fertilizer. As stated above any organic matter added to the garden will be decomposed by microbes into plant nutrients–they are all fertilizers. The important question to ask, “Is it a good source of fertilizer”?
Have a close look at the quote. Milk is a fertilizer. You can use it straight out of the bottle or dilute it to 1/5 the strength, and it gives the same benefits. THAT’S AN AMAZING FERTILIZER! Imagine a fertilizer that you can dilute to 1/5 and still get the same amount of nitrogen from it. I wonder if you could dilute it 100 times and still get the same amount of nitrogen? Or 1,000 times?
Clearly this statement makes absolutely no sense. Never trust an article that contains such rubbish!
Nutrient Value of Milk
If milk is a fertilizer then it is natural to ask how good it is. In other words, how much nitrogen does it contain. We are most interested in nitrogen because it is the nutrient that is most likely deficient in soil.
It turns out that that milk contains 3.1% protein, and protein is about 1/6 nitrogen. So milk contains 0.5% nitrogen. Compare that to bagged fertilizer that is 10 – 40% nitrogen and other organic fertilizers that have about 2% nitrogen. Milk is a fertilizer, but it is a weak fertilizer.
Cost of Milk Fertilizer
Plants can’t tell the difference between nitrogen from milk, manure or commercial fertilizer–see my post What is Organic Fertilizer for more details. Because of this it is always valuable to figure out the cost of any fertilizer.
Around here 3 L of milk costs around $5 which is 15 g of N. So if you are using milk you are paying $330 for 1 Kg of nitrogen.
Commercial fertilizer is about $12 for 1 Kg of N (10Kg bag of a 10-10-10 is about $12).
How about manure? Manure is about 0.6% N (wet weight), and 1 cu ft of wet manure = 60 lbs = 27 Kg. A cubic yard is 27 cu ft, so a yard is 730 Kg or 4.4 Kg of N. At $15 a yard, a Kg of N in manure costs $3.40. Buying composted manure in bags would be more expensive, but not nearly as costly as milk.
Milk is mostly water and so it does very little to build soil structure. Commercial fertilizer also does not build soil structure, but manure does.
So you have a choice. Use milk at $330/Kg nitrogen and get no soil improvement, or use manure at $3.40/Kg nitrogen and improve soil structure. Note that I have not misplaced the decimal point here. Nitrogen from milk is 100 times more expensive than nitrogen from manure.
Using milk as a fertilizer makes no sense! Try using it to control powdery mildew, but other than that it has no value in the garden.
Should You Use Milk?
If you have some spoiled milk it is better in the garden or on a compost pile than down the drain. But don’t use food quality milk to fertilize gardens or houseplants.
Just a note on the milk issue…
http://m.minnesotafarmguide.com/news/regional/milk-works-as-fertilizer-says-preliminary-study/article_028652ea-849c-11e0-9dcc-001cc4c03286.html?mobile_touch=true
I think more research is required on your part, I have been working with milk for the past 2 year and have seen some very stunning results but it is how it is used. It is not necessarily a fertilizer but aids in the break down of organic matter.
Are you affiliated with Monsanto? Why are you so negative when you here good results?
Re: “Are you affiliated with Monsanto? Why are you so negative when you here good results?” No I am not. What has Monsanto got to do with anything in this post? Why is it that when people disagree with science they immediately bring up Monsanto? Makes no sense.
I am negative in this post because I DO NOT have any good results. I have not been able to find any evidence that milk is any better than any other organic material. In fact I have only one study that looked at milk in agriculture and it showed no real benefits. It is on the list to be published.
Since Rod “had good success” with milk and clearly has better research information than I have been able to find, or else he would NOT have suggested I do more research, I emailed Rod to get some of this good research. Here is the email exchange.
From me: “I am interested at looking at more research. Can you send me some reports that have looked at Milk breaking down organic matter?”
Rod’s reply: ” When milk ferments it produces lactic acid bacteria . Like any other acid it breaks down organic matter. You don’t need a report to know this stuff.
I am careful about referring to any one scientist as it seems everyone has an agenda these days. ie: Monsanto Science, Government Science, University Science. They all require funding and that’s were we all go wrong. Don’t get me started.
I do my own research and believe it’s results. I was looking for more clues to using milk when I saw your site and was put off by your negative comments to someone who posted good results. Science is always in someone’s back pocket because it can not live on its own. At best if you can read between the lines and you can sift out the BS and find something meaningful just like with a myth. 🙂 ”
My comments on the email: Re: “You don’t need a report to know this stuff”. Interesting. We should believe in Rod’s opinion without any evidence to support the idea. Sorry – I’ll stick to the science.
I’ve written about the value of anecdotal data before in “Anecdotal Evidence – Not Worth The Screen It Is Displayed On”
I must admit the logic Rod presents is worth a look. “Milk produces lactic acid bacteria and …. the acid breaks down organic mater”. Yes as some bacteria break down milk they form lactic acid. And it is true that acid will break down organic matter.
Seems like a logical explanation. The problem is it might not be correct. First of all, very milk is being added to soil. So any acid produced will be quickly neutralized by the soil. See Increasing Soil Acidity.
Even if milk does break down organic matter, does soil need this help? Soil already has the bacteria needed to break down organic matter. That is why milk produced lactic acid.
The problem with explanations like this is that they might sound good on paper. But until studies show they actually work in the field – the theory is just that – a theory. That is why we need actual scientific studies to determine if milk actually breaks down organic matter faster than soil. And if this is true – is it a benefit to plants?
Clearly, neither Rod nor I have found such studies. But if you have them, send them to me.
Since writing the above I found another study http://mysare.sare.org/mySARE/ProjectReport.aspx?do=viewRept&pn=ONE12-155&y=2013&t=0. Like the previously reviewed work, it also shows little or no benefit from adding milk to soil.
Sorry Robert, but there’s not that much science in your post at all i see clear bias and a lot of opinion though.
The Mother Earth article you quote from stated that any milk has benefits but you only chose to quote the part that you could “debunk” i will say though i don’t think the studies performed thus far differentiated between raw or processed milk so who knows if raw is better or not…
heated milk is less effective? you say “not plausible”, you are approaching this from a perspective of the nutrients contained in milk being the primary reason for the claimed plant and growing benefits. as stated in the article the benefits are derived from microbial health in the soil. the heating of milk changes the sugars in milk – a quick google gave me this information.
People never used milk as a fertilizer in ancient times because they were always in a state of famine – …. just lol.. thats your whole theory on why the “ancients” probably never did this? i read often that the “ancients” often offered food and drink offerings to their gods so its entirely feasible that someone in the long forgotten past sprinkled milk over their garden or fields to “encourage blessings of the gods”
You then move into a nutritional comparison between direct nutrient fertilizers and milk when clearly the Mother Earth article states that the benefits are derived from a feeding of the micro-organisms in the soil greater aeration that in turn provide benefits to the plant.
Also if you are going to make that comparison please also notice that the article also stated molasses is to be used in conjunction with the milk. molasses has a lot more minerals (no nitrogen) but again, its not a direct fertilizer its there for the soil organisms
You cast doubt on whether soft bodied insects are poisoned by sugar because as you say bugs eat other things with sugar in them so it must be false… here’s some science for you buddy – there are many different sugars and they have varying molecular structures. not every organism can metabolise all sugars – as it happens milk contains a disaccharide sugar called lactose its basically an isomer of sucrose (same chem formula – different structure). We see in life that humans can have intolerance to lactose and have adverse effects due to being unable to metabolise because of the structure of the molecule. there are a myriad of other examples. in my opinion its entirely feasible that soft bodied insects are poisoned by the sugars in milk. btw sugarcane sugars and lactose are different and your analogy has no scientific basis because you are comparing apples with oranges here.
And last of all – i took a look at the study you posted in a reply to the comments about 2 vermont organic farmers experiencing little to no change after applying milk to their crops/pasture -0 the whole mechanism involved with using the milk in the first place is to do with rebuilding the soil flora and the boost in production is due to this improved soil health. both farms studied were already growing organic and as such probably already using methods to optimise soil health adding milk would have little additional benefit if this was the case – in my personal opinion.
i think you phoned this one in buddy. perhaps more reseach next time eh?
I notice lots of comments – but not one reference to support your claims.
You say “the heating of milk changes the sugars in milk”. Ok – so what? It still feeds the microbes – they don’t care if the milk has been heated.
The whole idea of feeding the microbes with ‘special food’ is promoted by many groups including Dr Ingham with soil food web, and compost tea. In none of these cases is there any evidence that the special food makes any difference. The chemistry is fairly simple – large molecules are broken down by the microbes into simple molecules which the microbes then use. The actual form of the original food is not that important. For more on the falacy of your logic here see my posts on Teaming with Microbes.
If the sugars are killing insects – give me a reference to support your claim!
Since I wrote this post I have reviewed some more scientific studies on the effect of milk in Milk Fertilizer – A Myth is Born. We now have proof milk does not work as a fertilizer.
Under ancient times, you write:
“I can’t honestly argue against this statement from a scientific point of view, but does it seem likely to be true? Would people in ancient times, when resources were low and famines were frequent, dump good milk on the fields in the hope of a bigger crop?? I kind of doubt it.”
Did you do any research? “I cannot argue…” and “I kind of doubt it,” are opinions.
below that, on powder mildew:
“There is some scientific evidence that this is true.” Any citation or explanation would be nice.
Your conclusions are not based on what can be concluded as actual research, with the exception the the reference to the study in Nebraska, where the public articles clearly state that the results from their experiment thus far are not enough data to conclude long term or fully replicable results. I noticed that you left that out information out of you article, as well as the link to that article for citation purposes.
I found your site when researching milk/whey applications. . I find it discouraging that folks may take your opinion for information as truth, when you have indeed not put forth enough research for you claims.
You are correct – the statement about ancient times is my opinion. I made that clear in the way I presented the information. It is my blog – I can have opinions.
The comment on milk being used on powdery mildew is just an agreement with the originally referenced link. It will be discussed more fully in a future bog post, but here is a link to one research paper I looked at: http://www.researchgate.net/publication/222480569_Effectiveness_of_cow%27s_milk_against_zucchini_squash_powdery_mildew_%28Sphaerotheca_fuliginea%29_in_greenhouse_conditions
I don’t understand your comment about the Nebraska study – I do not talk about a Nebraska study in this post.
awesome article! super useful for my science fair project! Thanks!
Should I dilute the milk with water?
Milk contains a certain amount of nutrients and organic matter per liter. If you dilute it by say half it has half as much per liter.
If you spread undiluted milk on 100 sq ft of soil, it will be the same as spreading the diluted milk on 50 sq ft of soil.
Adding water does nothing to increase or decrease the total amount of nutrients. It just might make it easier to spread over a large area.
I got four gallons of expired milk dumpster diving at a local store and I’m going to put it on my plants. Better than having it go into a landfill.
If you can’t eat it – you might as well use it in the garden.
I agree with you whole-heartedly; you can’t believe everything on the internet including some of your remarks. You disparaged an article in Mother Earth News but called the publication Mother Nature Earth News. If you misread the name of a magazine that’s been around since 1970 then maybe you misread the article. I don’t know which bugs/insects don’t have a pancreas but maybe they can metabolize plant sugars such as sucrose but not animal sugars like the lactose in milk. I suppose you’ve heard of some humans who are lactose intolerant? I can easily see how some bugs may be lactose intolerant, too. Do a search and look at how many types of sugar exist and where they come from. All sugars are not equal.
Thanks for pointing out my type on Mother Earth News – I fixed the mistake.
Sucrose is not a plant sugar – animals also have it as part of their biology.
All sugars are not equal – but the quote I analyzed did not specify which sugars are poisons – just ‘milk sugars’
As it turns out insects are lactose intolerant which is discussed in the following reference. It also says that milk has been tried as a diet for insects, but makes no mention of the fact that it is a poison to insects. https://books.google.ca/books?id=mcjECQAAQBAJ&pg=PA127&lpg=PA127&dq=are+insects+lactose+intolerant&source=bl&ots=EjGd0vJQ0S&sig=asTAYeTCmSjyBfwaYp46Qmqfgts&hl=en&sa=X&ei=l-F2VZfbHJKvyQTJgoLIAw&sqi=2&redir_esc=y#v=onepage&q=are%20insects%20lactose%20intolerant&f=false
“Sucrose is not a plant sugar – animals also have it as part of their biology.” Robert, I find it interesting that you say sucrose is not a plant sugar. The table sugar I put in my coffee comes from either sugar cane or sugar beets. Are these not plants? Perhaps I’m missing something in the science of making sugar.
When you originally said “they can metabolize plant sugars such as sucrose but not animal sugars like the lactose in milk” you were implying that there are two groups of sugars – from plants, and from animals. That is not the case. Most sugars are found in various life forms and are therefore not defined as animal or plant types.
i have many expired milk, in my home..
can i process the milk to organic fertilizer ?
Hope you reply 🙂
If you have expired milk that you can’t use in any other way, add it to the garden. If you have a lot of it, you might check to see if there is some way to compost liquids – I don’t know of any. But putting a lot on the garden may smell for a short while!
I would dump expired milk on the compost pile all the time. Just shovel it over and no smell at all.
U tend to forget that air is 70+ nitrogen and when you feed the microbes it grabs that nitrogen from the air. When you put commercial nitrogen on soil you will kill the microbes. You also lose porosity with commercial nitrogen over time.
Not sure why you think I forgot about nitrogen fixing microbes? I never said that you should not feed the microbes in the soil–only that using milk seems to be a poor choice for doing this when it can be used for food for people.
The statement “commercial nitrogen on soil you will kill the microbes ” is completely false. Commercial fertilizer when used in reasonable amounts will actually increase the growth of microbes. The nitrogen in commercial fertilizer and that which is released from organic matter as it decomposes is exactly the same chemical–how can one kill the microbes and the other not??
Not sure what you mean by ‘porosity’? Commercial fertilizers don’t degrade the structure of soil. It is the repeated cultivation of soil that is destroying the structure on conventional farms. This cultivation results in organic matter being decomposed more quickly, resulting lower organic levels, which in turn reduces the number of microbes. This has nothing to do with commercial fertilizers.
My question is not whether milk is a good fertilizer, but if milk is also a significant source of calcium for plants. I tend to have milk in the fridge that is past its expiration date and I was hoping I could add that to my garden instead of dumping it down the drain.
Calcium is one of the nutrients in fertilizer. So milk will add calcium to the soil at a rate of 300mg calcium per cup of milk. That is not a lot of calcium, and certainly not a good source of calcium, if your soil is deficient of calcium. Calcium carbonate would be a much better source.
Here’s the kicker–most soil is NOT deficient of calcium. Unless a soil test shows you that your soil is deficient, you should assume that it is not. If it is deficient, the test will tell you how much calcium you need to add, so you can figure out how much milk you need to get the job done.
Bottom line–milk will not hurt your soil and it adds some nutrients. Better in your garden than down the sink.
I assume you are posting the above link to show the huge value of adding milk to the garden.
The link makes some pretty big claims:
– research was done by the University of Nebraska to prove the claims
– Just 2 gallons of milk per acre produced “An extra 1,124 pounds [per acre] from one application”
– Milk also improved soil structure: “plots fertilized with milk was 18 percent softer than the control”
These lofty claims seemed a bit too lofty to be true. So I decided to contact Dr. Shapiro, the principal scientist at University of Nebraska who worked on this research. He was kind enough to send me the actual data resulting from this experiment, but asked that it not be released to the public, in part because it has not yet been published.
He did however provide this conclusion which I am free to publish. Dr. Shapiro said “there are no statistical differences between the control plots and the milk treated plots for either plant growth, or increases in soil structure”. The data backs this up.
This is a clear case of a “believer” taking the data and cherry picking the numbers that prove his belief. Then he writes about it and the author of the link provided in the comment, repeats the incorrect information, and we have just witnessed the birth of another myth.
I plan to write a complete blog about this example in the coming weeks. There is more interesting stuff to talk about.
Bottom line–you can’t believe everything that is on the internet. I always try to find scientifically published data to validate any position I take and I am always looking for better and newer data. I very much appreciate being informed of links such as above.
After reading an article on milk, I started to pour the dregs from my kids’ cups on a basil plant in my kitchen. Within a few days, the tiny flies that infested it disappeared and have never returned. I only watered with the milk, none on the leaves.
Perhaps the milk does something to the eggs or larvae of the flies? Maybe it simply coats them and suffocates them as the milk dries?
Maybe. Or the flies left for some other reason. The problem with such anecdotal results is that you can’t really reach any conclusions. This is how so many methods are started.
If you had several plants, all of the same kind, and all with the same kind of flies, you could test this. Put milk on half of them and see if half of them get rid of the flies. It is the only way to know that something actually works.
Or it works exactly how the MEN article described it! Youve seen it for yourself now…No need to tend to the naysayers lolol