Milk is an easy and free way to give your plants a nutritional boost while improving plant care.
Milk helps replenish soils nutrients.
Milk’s calcium helps plants grow.
Milks sugars yeild high crop volume.
Milk acts as a fungacide and a pesticde.
If it’s skim milk, you can pour or spray it directly onto your plant’s leaves – this is called foliar feeding. You can also use diluted milk to water your plants, which is better if you are using any milk other than skim.
If you are using a fuller fat milk, I’ve read that the fat isn’t good for the plant’s leaves, but you can still pour diluted fuller fat milk into the soil.
Milk can cure some of the fungus problems that plants are often susceptible to – the milk acts as a fungicide.
Diluted milk is great on tomatoes and other container garden vegetables, as well as annuals, perennials and even houseplants.
Microbes found in milk are great for compost! 
https://helpingninjas.com/milk-grows-cwe-gardens/
