Is Milk a Good Fertilizer

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Robert Pavlis

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.

bowl of milk with a large splash coming out of it.
Milk as fertilizer, source: placbo

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”

Soil Science for Gardeners book by Robert Pavlis

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.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

66 thoughts on “Is Milk a Good Fertilizer”

  1. If living things can’t tell between natural and synthetic why can’t living things survive on only vitamin supplements

    Reply
    • Jfyi. I use full cream milk with addition of 28%whey powder on my medical cannabis. With the addition of PK, during flowering my collars(?) Buds are the size of baseball bats!. Just saying

      Reply
      • And what are you saying?

        You are adding milk along with a bunch of other stuff and the plant grows. WWe know that when you add nutrients to plants they grow.

        Reply
  2. Have a dairy cow here and a garden. Got a bunch of dirt and what not sucked into the milking system and milk this morning. Diluting the milk 50% and pouring on the squash and other flowering plants makes total sense in the circumstance. These plants are growing mostly in compost but that doesn’t always have enough Calcium for some plants. The milk was going to have to be dumped anyways..using it as fertilizer mitigated losses as best and easily as I was going to.

    Reply
  3. Yes manure may be more efficient and cheaper for improving the soil structure. However, if one is on a pension and has limited funds one can purchase a 2 litre bottle of milk to mix with molasses and spray on the garden soil it only costs $2.39 in Coles supermarket , which then (in my opinion) enables the pensioner to improve the soil at a faster rate. Whereas, the pensioner would not get very much manure for the price of a 2 litre bottle of milk $2.39. My question is how much manure can one buy for the grand sum of $2.39?

    Reply
    • You agree that manure is more efficient and cheaper, and then go on to argue that milk is cheaper and more efficient?

      Manure is a lot cheaper than milk and it is 65% water, compared to milks 87%. Water adds nothing to improve soil.

      What does a pensioner have to do with the discussion?

      how much manure can one buy for the grand sum of $2.39? About 20L – 10 times as much, and that is not corrected for water.

      Reply
  4. I was searching online for an article like this, when I read reports that farmers are dumping unsold milk (during the pandemic crisis). It may not be an ideal fertilizer, but it doesn’t look like it will go to waste during an emergency like this

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    • Some areas also have milk quotas an excess milk is dumped.

      Seems like it would be better to powder it and send to people who need food.

      Reply
  5. So, I am going to do my own, documented test. Side by side comparison.
    Half will get everything I’ve always used with no milk and the other half with the same but with milk.
    You might be right but the only way to find out for sure is for me to do this test.
    I know it will not prove anything to anyone but me.

    Reply
    • Hii Timmothy,

      how is your milk as fertilizer test going on ? any result ?

      don’t mind to share with me, i am also very interested to know. i got own made yogurt gone bad.. hence i am thinking what to do.

      thx
      andrew

      Reply
  6. Greetings and thank you for this article. I happen to have A LOT of extra milk every week. So much that it goes bad or unused or thrown out which is wasteful. Can the milk be utilized for plants even if the outcomes are the same as any other fertilizer?

    Reply
  7. Is milk a good source for calcium for plants. I see pepper growers saying it is good and peppers use a lot of calcium. Wondering what your thoughts are on that.

    Reply
    • First question, do peppers need a lot of calcium? Probably not a lot more than other plants.
      Milk does contain some calcium, but most of it is water. If you are buying it for calcium it is a very expensive fertilizer. Solid calcium sources are quite cheap. If you have some free milk or it has gone bad – use it. But don’t buy milk because your soil test shows a deficiency of calcium.

      Reply
      • I have a few things to point out. I admire the sentiment of “but does it make sense?” For teaching other to strain out the garbage, but you’re applying it too narrowly. For example, when you ask if it makes sense that the ancients would waste good milk, you’re making several harmful assumptions, 1) that resources were always rare, and 2) all milk was always good, 3) accidents didn’t happen, 4) that using one resource to improve another was out of the question. You said it yourself, whole milk or cheese, it’s all the same to the bacteria, so spoiled milk fits easily within this theory.

        Secondly, your use of the “does it make sense” against milk sugars being harmful to pests. You need to remember a few species of bacteria and all mammals are just about the only organisms able to easily digest milk, and the thing that makes most animals and most adult mammals intolerant to milk is lactose, a milk sugar. You made the claim that either we were lied to or milk sugar is vastly different from plant sugars. Two chemicals can be similar chemically yet behave very differently. Take glucose and cellulose for example. Glucose is a sugar, cellulose is a hard to digest natural polymer- yet cellulose is literally just a bunch of glucose molecules linked together. Or take cellulose and lignin, lignin is much more rigid and hard to digest that cellulose, yet is literally just several cellulose molecules formed together.

        You have also made a strong financial case against using milk as a method of improving the soil, but you left out that milk is meant as a short term solution, a rapid-release source of nitrogen, and if the fed plants get composted, the nitrogen is recycled and what was a short term solution, has begun yielding long-term results.

        You used “than” where “then” was appropriate.

        Reply
        • Some valid points, but I don’t agree with “Two chemicals can be similar chemically yet behave very differently. Take glucose and cellulose for example. ” Glucose and cellulose might look similar structurally, but they are not similar chemically – hence the fact that they react differently.

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  8. I don’t go out of my way to use milk as a fertilizer what I do is rinse out my milk jug or if I happen to have a little bit of milk that has soured I will add water to that out shake it up I will let it sit on the counter overnight to build up a little microbial activity (cap on) and then I will fill it all the way up with water the next day and I will add it to my plants and it doesn’t seem to bother them at all….. I don’t stress out about it!

    Reply
  9. I have seen the use of milk in growing giant pumpkins by splitting a stem feeding a rag through it and soaking it in a container of milk. if memory serves it was in a wonderful film, “Rise of the Giants,” about competitive pumpkin growing.

    Reply

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