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Are Eggshells, Coffee, and Banana Peels Good for the Garden?

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Turn Kitchen Waste Into Homemade Fertilizer!

Should you be saving your eggshells, coffee grounds, and banana peels for the garden? Yes, they’re all free, natural ways to boost your soil’s fertility. Find out how to use kitchen scraps as fertilizer in the garden!  

Coffee Grounds in the Garden

Coffee grounds are a superb natural addition to any garden—wake up and smell the coffee folks! Have you had your morning cup of coffee? Great, but don’t be too hasty in throwing out those grounds! They’re a great source of nitrogen, contain some of the other two major plant elements—phosphorus and potassium, and are also a good source of micronutrients like magnesium, copper, calcium, zinc, manganese, and iron. Let’s get to using them.

  • The first use of coffee grounds is as a mulch around plants. Do not throw them onto the garden in thick clumps or layers; these mats together and form a pan, making it hard for water to penetrate. Ideally, sprinkle grounds over the surface in combination with other mulches (to stop it from forming a crust). You can sprinkle on top or mix in with the other mulch.
  • Don’t worry about coffee grounds being overly acidic. Most of the acidity is lost in the coffee itself upon brewing. They are a little acidic but with a pH in the region of 6.5-6.8, which is actually great for most vegetables. Besides, the quantity they are added at will have next to no effect on your soil’s overall pH.
  • Don’t dig coffee grounds into the soil; just leave them on top. Nitrogen isn’t immediately available to plants, but what will happen is that as the microbes in your soil set to work on the ground, nitrogen will gradually be converted into a form that plants can take up and use. This, in effect, makes coffee grounds—like other mulches—a very effective slow-release organic fertilizer.
  • Just a quick word of caution. Some plants won’t respond well to lots and lots of coffee grounds, particularly tomatoes, so do use them sparingly around your plants.
  • You can also add the coffee grounds to a compost heap. And this is where its relatively high nitrogen content can really power your compost. Despite being brown in color, coffee grounds are in fact a “green” (in composting terminology) and can be used to help balance out “browns” such as fallen leaves, straw, or shredded paper. Its small particle size means that it’ll start to get to work immediately. All those microbes will love it, breaking the nitrogen down into the plant-available form we’re after while generating plenty of heat to speed up the whole decomposition process and give your heap a pep in its step. Simply add generous handfuls of coffee grounds when you add your browns, broadcasting it over your pile.
  • Worms love coffee grounds, too—it aids their digestion. If you have a worm bin, this is also a great ingredient to add along with other ingredients. Seems like worms like their caffeine fix as much as we do!

Any coffee grounds you can save are superb, of course, but if you really want to up your game, why not have a friendly word with your local coffee shop? Many coffee shops are only too happy to give their grounds away, and some even leave them out for eager gardeners to haul away.

Tea Leaves

What about tea leaves or tag bags? Add tea leaves, too, but if you’re using teabags, bear in mind that most bags contain plastics, so if you’re going to add the whole bag, switch to a brand with fully biodegradable outers.

Eggshells in the Garden

Eggshells are a really rather fantastic source of calcium, as well as a host of other trace elements such as magnesium. So don’t shell out on expensive soil amendments; save your shells instead!

  • Before you use eggshells, sterilize them; we don’t want to spread salmonella around. Sterilize on low heat in the oven for a few minutes or in a microwave on high power for at least 10 seconds. Don’t rinse them, as this will wash away some of the organic matter from the shell, which you want to keep. And sterilizing the shells will make them clean anyhow.
  • Once your eggshells are sterilized, crush them up to increase their surface area or, better still, grind them up into a fine powder using a pestle and mortar, a high-speed blender, or coffee grinder. The calcium within an eggshell is locked up as calcium carbonate, making it unavailable to plants as it is. But by grinding it up into this fine powder, we’ve made it a lot easier for your soil life to get to work on it, turning it into a form plants can use. What we’ve done is turn eggshells into a fabulous slow-release source of calcium, ready to be released over several months.
  • Spread the eggshell powder over beds—just like the coffee grounds: sprinkled thinly onto the surface. Because this is full of calcium, we’d especially recommend this on beds that will contain plants prone to blossom-end rot. Note: The main reason for BER is actually due to irregular watering and the ability of the soil to take up calcium. However, as a general soil amendment, adding crushed-up eggshells can certainly help to add calcium to the soil as a precaution over time. 
  • Calcium helps promote the production of healthy cell walls, too, so this is going to be a real powerhouse for next season’s crops. Its high calcium content will also be great for leafy greens like kale and cabbage too.
  • If you have a wormery, worms absolutely love powdered eggshells. At this consistency, worms can easily ingest it, and it serves as a grit that, just like coffee grounds, aids their digestion and general health. And what do healthy worms mean? Better compost and better soil!
  • If you don’t have a worm composter, add them to your general compost pile to help the worms there. They’ll love you for it.

As an aside, eggshells (like coffee grounds) aren’t all that great at keeping slugs away. This is more of a myth!

Banana Peels in the Garden

Does a banana a day keep the doctor away? In any case, many of us eat bananas daily. And what do you get when you eat lots of bananas—lots of peels! Let’s do something with them…

  • Banana peels are a relatively good source of potassium, as well as some other micronutrients such as calcium. However, the value of these nutrients is often exaggerated. Some recommend soaking banana peels in water for several days to make a nutrient-rich tea, but in reality, what you get won’t be that strong or effective.
  • You could try drying them out in a low-heat oven to create a more concentrated powder. But really, the best thing you can do with banana peels is to add them to your compost heap, where they will—like other compost ingredients—rot down to release their nutrients into the final, crumbly compost.
  • When adding banana peels, make sure to remove any stickers or labels. And to speed things up, cut them up into smaller pieces. Bananas are a really fabulous addition to the compost heap because they do rot down pretty quickly—in a matter of weeks.

Wood Ash in the Garden

Last up is wood ash. Maybe you have ash from a wood fire handy? There’s usually plenty of it in the colder months!

We’re talking about good, clean ash from untreated wood. Ash from charcoal is fine, too, but avoid barbeque briquette ash and definitely coal ash, which has a very high sulfur content.

  • Wood ash is a great fertilizer, with good levels of phosphorous and potassium, along with trace elements like calcium and magnesium. In fact, that’s where the word “potash” (the name for nutrient forms of potassium) comes from because ash used to be collected in metal pots… pot-ash. 
  • The bits of charcoal you get—the partially burned wood—are biochar, which has an almost impossibly gigantic surface area of nooks and crannies that are great for soil biology—lots of homes for all those microorganisms that make outstanding soil!
  • Use your common sense, of course. Only collect it once it’s completely cooled down, and never mix hot ash with plastic! Metal tubs are best.
  • Like our other natural and free soil amendments, you can scatter wood ash right onto garden beds. It’s quite water soluble, though, and is easily washed through. Do add some in winter when it’s produced, but save some for the growing season, too. 
  • It’s great around most plants, and because it’s actually pretty alkaline, it’s a good one to use around brassica-family crops, like broccoli, which like the soil slightly on the alkaline side. Don’t use it around acid-loving plants for this reason—blueberries, rhododendrons, raspberries, and so on—and don’t scatter it where you want to grow potatoes next year because alkaline soils tend to encourage potato scab.
  • Its alkaline nature makes wood ash a great alternative to lime to help neutralize acidic soils. It’s about half as strong as lime, so you can use approximately twice as much to achieve the same effect.
  • Wood ash is a very handy addition to compost heaps and bins, too. This is because it helps to bring down the acidity of compost a little and also because those bits of biochar will help those magical microorganisms to do their thing. It will also add to the overall fertility of your heap. Spread over a thin sprinkling with every foot or so depth of material. 
  • Learn more about using wood ashes in the garden.

Nothing will go to waste in our household! Are you using any natural or organic soil amendments? Let us know in the comments below.

If you love growing your own food, why not take a look at our online Garden Planner?

About The Author

Jennifer Keating

Jennifer is the Associate Digital Editor at The Old Farmer’s Almanac. She is an active equestrian and spends much of her free time at the barn. When she’s not riding, she loves caring for her collection of house plants, baking, and playing in her gardens. Read More from Jennifer Keating

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Robert Thomas (not verified)

3 weeks 1 day ago

Uses if any of newspaper ashes?

Dear Robert Thomas… GREAT name! That’s the name of the founder of The Old Farmer’s Almanac!
Wood ash is good for garden compost; here is our guide, and newspaper ash can be mixed in with your wood ash. 

—The Editors

Janet Rich (not verified)

2 years 3 months ago

I compost oak leaves from my trees which break down slowly. Learning that coffee grinds acts as a green encourages me to seek more from coffee stores. I use all left over veggies and fruit and the eggshells. Thank you for the in-depth info.

Jerry (not verified)

2 years 5 months ago

We use a Keurig, so I empty out the pods before disposal and sprinkle the coffee grounds on my beds and in my compost heap.

Terrie F. Williamson (not verified)

2 years 6 months ago

I really enjoyed the video about coffee grounds, shells, wood ash. It basically confirmed what I already knew and have been doing, but it also taught me some things. In particular, about how to sanitize and grind egg shells, as well as the best ways to distribute the grounds, shells, and ash. One thing I do during the winter is spread my kitchen garden scraps and coffee grounds across my garden plot, working any remnants into the soil in the spring.