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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?

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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.

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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.

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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
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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
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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 8 '14 at 14:52
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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 8 '14 at 16:58

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