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During the dead of winter when the temperature was hovering consistently around 32F I took 3/4 gallon of milk that had gone bad and pored it on the grass near the back porch. To my amazement the grass sprouted up like it was summer time in a matter of days. It was dark green and some of it reached about 12 inches before slowing down. Its still chilly out and I started dumping my left over milk from cereal bowls in the same area and the grass turns even darker green within a single day.

What's in milk that my grass loves so much?

TugboatCaptain
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2 Answers2

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If you look at the label of any fertilizer, you will see three numbers (N-P-K). The first number is Nitrogen, which especially promotes leafy growth. Phosphorus promotes root growth and Potassium promotes overall strength, if you're wondering.

Milk contains a decent amount of protein, not just for humans, but also for plants. That's because out of all the macronutrients (fat, carbohydrates, and protein), protein is the only one that contains an additional nitrogen molecule. This nitrogen from the proteins of milk will promote the green leafy growth.

Milk has been legitimately used by a famous wax apple grower Lian Wu Hsiung (蓮霧雄) in Taiwan. He has used soybean milk and expired cow milk to make his fruit bigger and sweeter.

JoJo
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Nitrogen - milk contains roughly about 5% nitrogen as part of its protein content. Human urine, on the other hand, contains (roughly, it varies on time of day and the particular human) about 15% nitrogen - I leave you to draw your own conclusions as to which will cause more green growth, though the most effective and cleanest use for the latter is adding it to the compost heap occasionally.

Regardless of milk's nitrogen content, I wouldn't describe it as a 'good' fertiliser because it's not balanced.

UPDATED ANSWER (in response to both comments)

Yes, I am serious about urine on the compost heap. The first one in the morning contains the most nitrogen, so collect that and use it, if your heap is a bit short on nitrogen giving materials (such as green leaves). I used it for years, used to collect it from my kids, saved money on compost activators, but I didn't use it every day, probably about once a week during spring and early summer particularly.

Stranded Pirate: I know that human urine does contain nitrogen, not only from the scientific point of view, but from experience, and not the one I'm mentioning above. I had a client some years ago, an older couple, and she was puzzled as to why the grass nearest the french windows, just beyond the path outside, was lush, long and green in February and March when the rest of the lawn wasn't. I took the husband aside and he confessed - his arthritis made it difficult to get upstairs, so when his wife went to bed, he'd stay up and watch tv, and if he needed to, he used to nip outside to pee instead, without her knowledge. I never told her, just suggested he might want to spread it around a bit more.

Bamboo
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  • If milk is not balanced, what about urine then? Are you serious about your compost proposal? I mean, what about the 85% which are not nitrogen. There are some acid parts, aren't there? – Patrick B. Feb 17 '14 at 22:33
  • I know from first hand experience that urine does nothing to promote grass growth whatsoever ;) If the nitrogen content of urine is that high then clearly there is something else in play for the milk to cause such rapid growth. – TugboatCaptain Feb 18 '14 at 16:28
  • @PatrickB. I'm pretty sure you're in Europe - check any British gardening website and its full of people making jokes about siting their compost heaps beneath the bathroom window - for obvious reasons, provided their aim is good. Loads of people here use it... – Bamboo Feb 18 '14 at 17:02
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    How funny and how cool...a whole new world you've opened for me. We see dogs pee on an undernourished lawn and the lawn gets a big green spot, then a dog pees on a healthy lawn and burns it. DUH! I am having so much fun. Of course urine has nitrogen in it! I am thinking of these piles of wood chips we had dumped by the electrical company cleaning up trees beneath their lines. I used to use kitty litter made of alfalfa pellets which worked great until the clumping stuff came about. We live in a Yurt...no bathroom yet! Got a little septic system but my 'chamber pot' could go to good use! – stormy May 29 '14 at 19:04
  • @TugboatCaptain I've read about urine as fertilizer. If you don't dilute it considerably, it may harm your plants instead of helping them. So, that may be why it did not help your lawn. My concern about human urine is that it may contain harmful chemicals, pathogens, parasite eggs and medications. If you're taking medication, I wouldn't recommend using yours at all. I would personally want to sterilize human urine before considering it for fertilizer (boil it outside or something). I've heard about human waste causing communicable diseases, although I don't know how common that is. – Brōtsyorfuzthrāx Oct 08 '14 at 00:15
  • @user2962794 - human urine is sterile as it leaves the body, which is why people can drink it in desperate situations and survive. The human waste you need to worry about is fecal matter. – Bamboo Oct 08 '14 at 08:33
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    The issue with urine and lawns can be the salt, as well as too much nitrogen (e.g. where pets have a favourite spot). – Chris H Oct 08 '14 at 14:52
  • @ChrisH: pet urine is not good on lawns, (or sprayed up against plants) specially bitch urine, burns the hell out of it. – Bamboo Oct 08 '14 at 15:22
  • Human urine (or any urine) is definitely not sterile when it leaves the body. Many live parasite eggs pass in urine. – Brōtsyorfuzthrāx Oct 08 '14 at 16:26
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    @user2962794; well, another myth debunked, and its obvious now I think about it - a bit of quick research shows it was thought to be sterile from the point of view of bacterial content, but it has been disproven, so I was wrong! Ah well, you learn summat every day - I'd still drink it if I was dying of thirst in a desert though! – Bamboo Oct 08 '14 at 16:58
  • @Bamboo that's my point - it's too concentrated. – Chris H Oct 09 '14 at 18:25
  • @Chris - I saw something online yesterday that said that, but have a conflicting source of info re both sterility and concentration - methinks I'm going to have to do more in depth research. Experience of my client peeing in the same areas of lawn at night for 6 months certainly didn't confirm it burned anything,just the opposite - produced lush green growth, but it was winter, possibly with plenty of moisture around outside. It's piqued my curiosity... – Bamboo Oct 10 '14 at 10:52
  • @Bamboo I'm sure it depends on the local conditions. Composition will vary too - when it comes to humans you might find a significant difference between a vegan with a serious tea habit, and someone whose only fluid consumption is protein shakes and the odd beer to go with a steak. – Chris H Oct 11 '14 at 07:49