You may have heard or read that milk is sometimes used to help grow tomatoes–and also squash.
Is it a fertilizer?
Milk contains calcium (Ca). Calcium is an important plant macronutrient. Macronutrients are foods that help plants grow and function. Calcium helps build plant cell walls which in turn allow the transport of other plant nutrients. Also calcium level in the soil controls the soil pH (pH is a chemical balance that allows plants to operate, or not). If calcium is washed out of the soil, the soil will become more acid and can affect plant growth. (Agricultural lime such as dolomite lime contains calcium.)
If you feed plants milk–whole milk or powdered milk–you are feeding plants calcium.
So milk can be a tomato plant fertilizer: Sprinkle a quarter to a half cup of powdered milk on top of the soil after planting, and repeat every two weeks throughout the growing season.
What else does milk do for plants?
Milk is a fungicide.
Old-time garden wisdom AND recent scientific plant research say that milk contains fungicidal properties. If you spray milk on plants, it will control the growth of bad fungi.
Fungi are microscopic organisms. A handful of soil contains thousands and thousands and thousands of fungi. There are good fungi and bad fungi. Good fungi help build the soil by breaking down organic matter into nutrients plants can use. Bad fungi are parasites that feed on plants. Bad fungi include mildews (downy mildew, powdery mildew), rusts, rots (root rot, damping off, fruit rot), canker, scab, spot (black spot and anthracnose), wilts (fusarium and verticillium) and smuts (and black sooty molds caused by black sooty fungi spores).
Fungi are spread by spores. They germinate and root much like plants. When a fungi takes root as a parasite on plant tissue it feeds and begins to grow. A fungus can be prevented from rooting and can be removed (prune off the infected plant tissue and throw it away in a paper bag so that the fungi spores do not spread). Fungi allowed to grow will spread via spores floating on the wind or swept along in a drop of water.
Fungicides rarely kill fungi. They are most useful as a preventive, not as a cure. Fungicides cover plant tissue and do not allow fungi to root.
Plant researches in Brazil and Australia have recently used milk as a fungicide on vegetable crops, grapes, and flower crops. They found that spraying a dilute mix of 1 part milk and 9 parts water prevented fungi from growing. (The researchers also believe that the potassium phosphate in milk helps boost the plant’s immune system and may also work as an antibiotic.)
Once again, milk–like other fungicides–does not cure fungal diseases but helps to prevent them. Milk keeps fungi from growing and spreading.
A note: skim-fat milk works best; the fat in whole milk may clog up your sprayer. As well, reconstituted powdered milk will work.
Tomato disease fighter formula: combine 1 part skim milk and 9 parts water. Spray the plant every two to three weeks until mid-summer (most fungal diseases have run their course by mid-summer, except where the weather stays warm and humid).
Thank you very much. We are doing an experiment about what is the effect of types of liquid on plant’s growth. I was asssigned to research facts about milk and what in it will possibly affect growth of the plant, height growth particularly. Thanks. I’m a 6th grader student of Salk School.
Your very welcome. It’s great to hear from a sixth-grader doing plant research. The calcium in milk not only helps build plant cell walls, it also helps build strong bones in sixth graders. Thank you Tina and Harry for writing. I am sure your research will turn up very interesting information on plant growth.
Hi I have some of my husbands protein powder that’s milk based it also has vanilla flavor would that be ok to use or would the added flavores like the vanilla and sugars hurt the plants?
Some non-natural, manufactured additives may stunt or harm plants. You can do a simple test, by using the protein powder on a few plants and compare the growing results to the plants you not treat with the powder. Keep a simple day-to-day log of your observations.
thank you very much for this information that i really need for my science fair project about how will milk effect plants growth now what are in the milk and how are they useful. I”M a freshman at waipahu high school.
can you use milk that has spoiled and have the same benefits?
I have not used spoiled milk, but it should work. It is the calcium in the milk that benefits the tomato.
when you say 1 part to 9 parts what is that exactly?
In these instructions if 1 part were 1 cup then 9 parts would be 9 cups. If 1 part was 1 gallon then 9 parts would be 9 gallons. You can determine what amount is 1 part.
So wait, does milk also help other plants grow besides Tomatoes and Squash?
Yes, milk is a good source of calcium for plants (and humans). It contains beneficial proteins, vitamin B, and sugars that can improve overall plant health and yield. Milk can replace the lack of calcium that causes blossom end rot in squash, tomatoes, and peppers. Do not use milk as a fertilizer at full strength–dilute the milk by 50 percent with water.
I have just read your article on adding milk to tomato plants. It contained a common misconception. My understanding is that it is the carbonate in the lime or dolomite that neutralizes soil acidity, not the calcium content. Therefor other compounds containing calcium may or may not alter the pH depending on what else is in the compound. For example gypsum contains lots of calcium but does not change the pH. Of coarse the addition of calcium will have other benefits if there is a calcium deficiency in the soil.
Information about powdered milk with gardening is great…thank you
Your sight looks interesting
Thanks for reading Harvest to Table.
There is one side effect when you add 3 Tablespoons of Blackstrap Molasses per gallon of the milk mixture! It turns out as a lot of insects have Diabetes and can not digest sugar two of these bugs are grasshoppers & Aphids and it gives them stomach aches In other words it acts as a natural insecticide and the nice thing is it is selective and will not bother any beneficial insects!