Are Eggshells, Coffee Grounds, and Banana Peels Good for the Garden? | Almanac.com

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


Find out how to use food scraps and wood ash as soil superfood!

The Editors

Coffee grounds, broken eggshells, banana peels, wood ash, and tea bags can really pile up! Are they truly good for garden soil and plants? Which plants benefit from them the most? Find out how to use food scraps and firewood ash as soil superfood!

Let’s look at some common items of kitchen and household waste in the garden. They’re all free and natural! How can they boost your soil’s fertility? 

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 on and use them.

  • The first use of coffee ground is as a mulch around plants. Do not throw them onto the garden in thick clumps or layers; this ats together and forms a pan, making it hard for water to penetrate. Ideally, sprinkle grounds over the surface in combination with other mulches (to stop it forming a crust). You can sprinkle on top of or mixed in with the other mulch.
  • Don’t worry about coffee grounds being overly acidic. Most of the acidity is lost into the coffee itself on brewing. They are a little acidic, but just 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. The nitrogen isn’t immediately available to plants, but what will happen is that as the microbes in your soil set to work on the grounds, that 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 it’s relatively high nitrogen content can really power your compost. Despite being brown in color, coffee grounds are in fact a ‘green’, and can be used to help balance out ‘browns’ such as fallen leaves, straw or shredded paper. It’s small particle size means 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!

Learn more about how to attract earthworms! Your garden will thank you for it.

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 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 a 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 in essence done is turn eggshells into a fabulous slow-release source of calcium, 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 thison beds that will contain plants prone to blossom end rot, a disease caused by calcium deficiency: so tomatoes, peppers, courgettes or zucchinis and the like.
  • 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

A banana a day, helps 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. But 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 drying them out in a low 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 labels. And to speed things up, cut them up into smaller pieces. Bananas are a really fab addition to the compost heap because they do rot down pretty quickly – in a matter of weeks – and especially at this time of year when there’s less coming off the garden.

Wood Ash in the Garden

Last up is wood ash. If you have ash from a wood fire here, there’s plenty of it in the colder months!

We’re talking about good, clean ash from untreated wood. Ash from charcoal’s 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 up 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 commonsense 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 onto beds. It’s quite water soluble though and is easily washed through, so do add some in winter as 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.

And if you love growing your own food, why not take a look at our online Garden Planner.

2023 Almanac Club

Janet Rich (not verified)

10 months 4 weeks 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)

1 year 1 month 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)

1 year 1 month 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.