Feeding Plants From the Kitchen – Which Products Actually Work?

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Robert Pavlis

What do you give plants to drink besides water and plant food? This question was asked on Facebook and I was surprised at the number of household kitchen products that are given to plants. What did not surprise me was that not a single person provided any evidence that any of them actually worked.

A very common expression people use to justify their actions is, “my plants love it”.

I hate that phrase. Plants do not show love – they don’t even say thank you. If you give something to a healthy plant you have no way of knowing if it is harming the plant or doing some good, unless you see huge changes in the plant, and even then the changes could be due to any number of other causes.

In this post I discuss 13 items people feed to plants.

Feeding Plants From the Kitchen - Which Products Actually Work?
Feeding Plants From the Kitchen – Which Products Actually Work?, source: Kitchn

Giving Food Scraps to Plants

Many of the items given to plants from the kitchen are food scraps and almost all contain water. Provided the product does not contain toxins, the water in these products is good for plants.

Gardeners understand the value of water, but they think that the other ingredients in the water are beneficial too. For the rest of this post I will ignore the water and focus on these other ingredients – the chemicals.

Compost Science for Gardeners by Robert Pavlis

The discussion here applies to both houseplants and garden plants. If you fertilize your indoor plants, none of these items do any good because your plants already have enough nutrients. In a garden with healthy soil, they will do very little because the soil provides all the nutrients plants need.

Banana Water for Plants

This seems to be the new hot DIY plant food this year. People take banana peels, put them in water and let them sit in the sun for a few days to make a yellow colored banana water. The claim is that it contains all kinds of nutrients, especially potassium – which plants need.

I have reviewed this in The Magical Power of Banana Peels in The Garden – Or Not. There are almost no nutrients in banana water, so it is of little value to plants.

It is just this years gimmicky thing to do.

Beer for Plants

What is in beer? Other than water, alcohol is the main ingredient, and this can feed microbes but has no value to plants. Next highest ingredients are carbohydrates; again no direct value to plants. There are 1-2 g of protein per serving, so beer adds a bit of nitrogen, but we are talking small amounts. It also adds small amounts of calcium and magnesium, which are rarely deficient in soil but may benefit a soilless mix.

A recent study found that alcohol stunted the growth of paperwhite narcissus but did not affect flower size.  “Dilute solutions of alcohol – though not beer or wine – are a simple and effective way to reduce stem and leaf growth.”

As you can see, beer has very little to offer plants. It’s better to drink the beer, collect your urine and use that to fertilize plants.

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Growth of paperwhite narcissus is stunted by alcohol (from left to right, 0%, 1%, 5%, 10%, 25%)
Growth of paperwhite narcissus is stunted by alcohol (from left to right, 0%, 1%, 5%, 10%, 25%), Credit Miller & Finan

Coffee for Plants

Would you give these carcinogens to your plants: acetaldehyde, benzaldehyde, benzene, benzofuran, benzo(a)pyrene, caffeic acid, catechol, 1,2,5,6-dibenzanthracene, ethanol, ethylbenzene, formaldehyde, furan, furfural, hydrogen peroxide, hydroquinone, isoprene, limonene, 4-methylcatechol, styrene, toluene, xylene? I am sure you are shaking your head, NO! Well, that is exactly what you are doing when you give coffee to your plants. And you ingest these when you drink the coffee.

Don’t worry, their levels are so low that they won’t harm you or the plants.

Black coffee without sugar has nothing in it that is of value to plants. If you add some milk or sugar, then that might help plants a tiny bit. Milk is discussed in its own section below and sugar is discussed in the soda pop section.

There is one other thing to consider; the caffeine in coffee is toxic to plants in larger doses. The amount in a cup of coffee is quite small, but caffeine is not good for plants.

Sugar Water for Plants

Sugar water might actually be good for plants if you use it correctly. Get the details in Is Sugar Water Good For Plants.

Does it keep Christmas trees fresh longer? No, just use plain water.

Compost Tea for Plants

I have discussed this extensively. There is no evidence that this is any better than using compost.

Compost Tea NPK Values

Compost Tea – Does it Work?

Fish Tank Water for Plants

Not exactly a kitchen item, but you might have the tank in the kitchen?

Fish poop! This adds nutrients to the water. The level of nutrients is going to be low, but it is enough to grow aquatic plants and algae, so it will have some value for plants.

Nitrite levels above 0.75 ppm in water can cause stress in fish and greater than 5 ppm can be toxic”. Plants want a nitrogen level of 100 ppm. You can see that “fish water” is a very low level of fertilizer.

Gatorade for Plants

The claim here is that plants need electrolytes.

Electrolytes are essential minerals like sodium, calcium, magnesium and potassium, that are vital to many key functions in our bodies and in plants. Assuming Gatorade contains some electrolytes, they will only help plants if the soil they are growing in is deficient in those electrolytes. This is something few gardeners understand. Adding more fertilizer to soil that has enough nutrients will not help plants.

From the Pepsico website: “Gatorade Thirst Quencher, Gatorade Endurance Formula and G2 contain sodium and potassium, two electrolytes lost in perspiration that play an important role in hydration and muscle function”.

I have never heard of a soil that is deficient in sodium (plants need very low levels) but we do know that higher levels of sodium are toxic to plants. Pouring more sodium on plants is not a good idea even if they get some potassium along the way.

YouTube video

Milk for Plants

I see many claims for the power of milk and even some farmers use it on their land as a way to fertilize it. I have reviewed this in some detail in Milk as Fertilizer.

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 a weak one.

The problem with milk is that it is a very expensive fertilizer. “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”. If you have spent milk, by all means add it to the garden, but don’t waste good milk.

Milk can be sprayed on plants to stop powdery mildew.

Molasses for Plants

Molasses does contain some plant nutrients and a lot of sugar. Should you add it to gardens – No.

To find out more see Molasses for Plants.

Pasta Water for Plants

The way to cook perfect pasta, according to the experts, is with salty water. Salty water boils at a higher temperature which produces better tasting pasta. If you salt your pasta water (I don’t), then it should not be used on plants – sodium is toxic to plants.

What about salt-free pasta water? It contains starch, which is made up of carbon, hydrogen and oxygen. The plant does not benefit directly by having this added to roots. Starch will feed microbes which in turn will improve soil, but the amount of starch we are talking about is so small it has no real benefit for the garden.

Rice Water for Plants

Rice water is used for many things including diarrhea, skin care and preventing dandruff. Could it help plants?

It is unlikely. The water will contain some starch and some low level of nutrients, but adding this to soil will have almost no effect. Besides if you cook rice correctly, there is no rice water produced.

However, rice does contain arsenic and either soaking or cooking with excess water does remove some of the arsenic.

Soda Pop for Plants

This topic is a bit more complicated. I’ll assume all pop contains CO2 in the form of bubbles. They all contain some nutrients. Some contain high levels of sugar.

Some people report better growth when using things like club soda (low sugar level) and contribute this to the CO2 bubbles. This explanation is unlikely to be true if the plant is growing in healthy soil because plant roots don’t need CO2. Maybe it would help break up very compacted soil?

One study grew Helzine soleirolii, commonly known as Baby’s Tears, with and without club soda. Club soda produced better growth, probably because of the extra nutrients. Any soda pop containing nutrients would provide these to plants, and we know that helps plants grow. This will be more effective in a pot, than in the ground.

Some pop also contains sugar and this can be beneficial or not, depending on the dose. Sugar is not absorbed by plant roots directly, but it can feed microbes, which in turn provide plant nutrients. At higher doses the sugar can actually starve plants. Sugar water (i.e. pop) has a low osmotic pressure and when this is next to plant roots it will suck nutrients and water out of the plant, which clearly is not good for the plant. Some non-scientific sources claim that high sugar levels may also help pathogenic microbes become more dominant in the soil, but I have my doubts about this.

Soybean yield was not improved by foliar sprays of sugar (cane sugar, corn syrup or molasses). In another study, applying dextrose or sucrose as a foliar feed on corn and soybean, did not increase yield.

Addition of sugar as a foliar application does not seem to improve plant growth.

Diluted soda pop will probably not harm plants, but it won’t help a lot, especially if you have been fertilizing regularly. High sugar pop, added to small containers, might cause harm.

What about Coke? There are lots of claims that coke will harm plants more than other types of soda pop, but I found no reliable reference that makes such a claim. I think this myth stems from the fact that coke is believed to dissolve steel nails and therefore it is bad for us and plants. The truth is that coke does not dissolve nails, at least not in a few days.

coke does not dissolve steel nails
Coke does not dissolve steel nails, source: Josh Madison

Coke also has a pH of 2.3 due to phosphoric acid. At that pH is is probably not a good idea to add to potted plants, but it won’t harm soil in the garden, provided you don’t pour it on the leaves.

Tea for Plants

This is described fully in Is Tea a Good Fertilizer for Houseplants?

Think of tea as being a very low level fertilizer. It won’t harm plants, but won’t do much for them either. Putting cold tea on plants is OK, but don’t brew tea for the plants – a complete waste of time and energy.

If you are concerned about pH, use black tea for alkaline soil, and green for acidic soil. Or stick to herbal tea which has the least effect on pH.

  • Black 5 to 5.5
  • Green 7 to 10
  • Herb 6 to 7

Vegetable Water for Plants

This is the same as other sources of boiled water. It does contain very low levels of nutrients. It won’t harm plants, but it does not do much for them either.

Should You Use Kitchen Scraps on Plants?

The truth is that most of these products will not harm plants, but they don’t do much good either. The more diluted they are, the less value they have.

They do all provide water which is good for plants.

If you don’t want to waste the item, use it on plants or in the garden. But please, don’t go out and buy these things because someone told you they were good for plants.

 

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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!

17 thoughts on “Feeding Plants From the Kitchen – Which Products Actually Work?”

  1. A Friend told me to put tea leaves on my limp Orchid, so I did. After a few weeks it is bearing a new leaf and holding up beautifully. I put a mixture of green and black tea bag leaves on it. I have also put the tea leaves on the rest of my inside pot plants and they are looking great. I am patiently waiting for my Orchid to Flower now.

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