When You Should (and Shouldn’t) Use Coffee Grounds in the Garden
Coffee is so ingrained in modern culture that people produce about 15 million tons of used coffee grounds every year. So people spent years trying to figure out what to do with these lands.
One of the most common uses that I keep reading about is that you can throw your used soil directly into your garden. As with many gardening tips, there’s a lot to be said for this: Throwing used coffee beans into the garden willy-nilly isn’t a good idea, but there may be some niche uses where it makes sense.
What’s actually in coffee grounds?
Let’s start with what’s in coffee grounds. Coffee itself is a grain, and all beans are nitrogen fixers by nature, meaning they produce available nitrogen for the soil. In addition to protein, beans also contain oil, lipids, triglycerides, fatty acids, cellulose and sugars. Additionally, lignin (an organic polymer), phenolic compounds (an aromatic substance), and essential oils can be added during the brewing process, none of which cause problems in the garden and may actually be antioxidants. There are three organic bodies that can break down and use all of these compounds in the garden: fungi, soil bacteria and earthworms. So far so good, right?
Debunking common gardening myths about using coffee grounds
Myth 1: Coffee grounds acidify the soil.
So, to dispel the first myth about coffee and your garden, adding it to the soil around blueberries, hydrangeas and azaleas will not create the acidic environment that these types of plants enjoy.
Coffee beans form an acidic brew, which will be harmful to your garden since you want to keep the pH level of your soil as close to neutral as possible. However, ground coffee actually has a neutral pH or close to it. This is partly because by the time the coffee is ground, most of the nitrogen has disappeared, creating a carbon to nitrogen ratio of almost 1:1. Instead, use a fertilizer specifically for these plants, which will help acidify the soil.
Myth 2: Coffee grounds should be used as an antimicrobial agent.
Another common coffee-related tip from gardeners is that coffee grounds can help prevent pathogens such as fungi and viruses from growing in your garden. There is some truth in this, but it is a double-edged sword.
Evidence shows that coffee grounds may have slight antibacterial and antimicrobial effects on soil, but these results vary, which makes sense since there are so many types of coffee, and a lot depends on the brewing and roasting process. Remember, however, that microbes are not all bad—and in fact, good microbes like mycorrhizae (fungal structures) keep your garden thriving. Coffee grounds don’t discriminate, so if they get rid of germs, they get rid of them all.
Myth 3: Coffee grounds are good mulch.
Finally, coffee grounds make excellent mulch. Dr. Linda Chalker-Scott is quoted in an article from the University of Arizona Cooperative Extension saying that the soil is so finely ground that if left on the soil in large quantities, it can impede the flow of air and the penetration of other elements, which is harmful to the environment. garden.
Coffee has additional downsides, including caffeine, which can slow down plant growth . Additionally, although it contains potassium, phosphorus, calcium, magnesium and very trace amounts of iron, copper, manganese and zinc, the available amounts of each are so small that they can be neglected in the garden. As is usually the case with gardening myths, while every myth has a little truth to it, the reality is that there are products that can achieve the goal much more effectively. In this case, garden fertilizer.
However, coffee does show promise as a slug and snail repellent.
Apparently, the only thing coffee grounds can do is help control slugs and snails. In an article from Oregon State University Extension, a soil scientist named Linda Brewer reports that research has proven that very mild brewed tea with water poured into the garden can significantly reduce slug and snail populations. More addictive and more effective than commercial products like Sluggo.
She recommends making a solution of one part water and two parts strong brewed coffee, then pouring it over the soil. You can also use it as a foliar spray if slugs are feeding on your vegetables, such as cabbage. In this case, use nine parts water to one part brewed coffee and spray it on. At these low concentrations the acidity is reduced so this shouldn’t be a problem, but you should always test a solution like this on a small area on a cloudy day before applying it throughout the garden.