If you're looking for ways to improve the health of your garden and reduce food waste at the same time, look no further than your own kitchen. Many common kitchen scraps can be used as soil amendments, providing valuable nutrients to your plants and helping to reduce the amount of food waste that ends up in landfills. Let’s look at some very common ones.
Banana Peels. These scraps are packed full of nutrients that are beneficial to plants. There have been studies using banana peels on everything from Swiss Chard and tomatoes, to potatoes and peas. And whether the banana peels were made into a compost, an extract, or simply dried and added to the soil, the results showed the banana peels made a difference in the growth of each of the treated plants compared to the control.
What these different studies showed is that there is a number of minerals and nutrients available in the banana peel that becomes available to the plants once the peels are broken down, not just potassium: iron, phosphorous, calcium, amino acids, citric acid and proteins were all made available to the crops and likely work together in increasing the plant sizes and harvests in different ways.
So, how do we add our banana peels directly into the garden or into our potted plants if we’d like to see faster results than our compost can give us? The easiest way I saw in one of the studies was to dry the peels in the sun, shred them up into small pieces and add 3 tablespoons of the peels for every 8 and a half pounds or 4 kg of soil. One other interesting study showed that an aqueous solution (in other words, banana peel tea), or a fermented solution, showed significant differences in growth of hydroponic lettuces. So, it’s easy to see how that benefit could translate into our soil-grown plants.
Egg Shells. These contain calcium, which is essential for plant health and can be beneficial to overall yield, but it’s important to use them properly. In studies using eggshells as a fertilizer the shells were usually washed, dried, and ground into a fine powder in a grinder. In fact, in one of the studies the dried shells were made into a tea in addition to the powder and the results showed the benefits of using the powder directly were significantly better than as a tea.
Now this doesn’t mean if you’re using eggshells that you absolutely have to grind them into a powder for them to be beneficial. You can just crush them and sprinkle them over the soil and they will, eventually, break down and release the calcium and other minerals into the soil. It’s just more effective and faster acting when done as a powder.
Tea Leaves and Coffee Grounds. The news is good for the garden regarding tea leaves. Tea leaves contain potassium, phosphorous, nitrogen and tannic acid, all important for plant growth. As the tea leaves decompose, they increase soil nutrients which in turn promotes the activity of the beneficial microorganisms and improves soil oxygenation which strengthens the root system of plants. The studies I found showed positive results in overall growth in the experimental plants compared to the control. And the tea leaves had just been dried and mixed into the soil.
The news on the coffee grounds, though, isn’t as clear cut. In fact, it’s the only household waste item I found that had such mixed results in studies. There are many studies that concluded that coffee grounds are good for the soil and good for the plants, increasing plant growth and often times helping to keep away pests like slugs. There are also experiments being done to reduce the amount of peat moss being used in potting soils by replacing some of it with spent coffee grounds. There were also some interesting studies where the coffee grounds increased the organic carbon levels in the soil and improved the soil aeration, but resulted in decreased plant growth.
And, then there were the studies that showed the spent coffee grounds being downright detrimental to plant growth. One study grew broccoli, leeks, radishes, violas, and sunflowers in three different types of soils with and without spent coffee grounds and fertilizer amendments and ALL of the plants grew poorly in response to the coffee grounds. Another study used fertilizers created from spent coffee grounds and found them to be toxic to certain plants in certain soil types.
In looking at all the research, what I’ve gathered is that there are components of spent coffee grounds that may be toxic to soil microorganisms and plants, but at the same time these toxins provide a natural pesticide and herbicide. And that much of this is dependent on when and how the coffee grounds are used. Everything points to using spent coffee grounds sparingly if used fresh or composting it fully before use.
So, for most everything it seems there are nuggets of truth for all these amendments. Dry the banana peels and the egg shells, grind them up and put them in your soil. Dump the tea leaves in there too, but maybe compost the coffee grounds before using those. All of these things are going to add essential nutrients to our garden soils and it will keep that kitchen waste out of the landfills, which is a win all around.
Your Friend in the Garden,
Resources: Ep. 145 - Kitchen Waste as Plant Food: Egg Shells, Banana Peels, and Tea Bags, Oh My!