What Plants Like Coffee Grounds And Eggshells? [2024 Updates]

Cracked eggshell on forest floor amidst natural debris, hinting at garden composting elements.

Instead of throwing your coffee grounds and eggshells in the trash, consider saving them for your plants.

Those everyday kitchen scraps are full of energy and nutrients, and when used wisely, they can be highly beneficial for the garden. They will give plants a boost of natural nutrients while reducing waste.

In this article, we will share, in more detail, our experiences with plants that will benefit from nitrogen uptake in coffee grounds and those that prefer the calcium goodness of eggshells. We will also explain the downsides of using coffee grounds and eggshells and their positives for maximum results in your indoor and outdoor garden. 

Let’s explore how your breakfast leftovers become food for your soil!

What Plants Like Coffee Grounds?

Coffee grounds contain essential nutrients such as nitrogen, potassium, phosphorus, calcium, copper, chromium, iron, and magnesium. While these nutrients can be highly beneficial to various plants, coffee grounds can also affect the pH levels of your soil. This means knowing the level best suited to your plants is essential. Once you understand your plant requirements, you can provide the ideal growing conditions to suit their needs. A good indication of pH levels and soil conditions is observing nearby plants growing well. However, as the pH levels can change with added fertilizers and coffee grounds, or you notice some plants struggling, it is wise to use a pH level soil test you can purchase from garden stores or online. 

The following are some plants that will benefit from the use of coffee grounds as a fertilizer, either applied directly into the soil or as a ‘liquid’ fertilizer:

Fruiting Plants

  • Citrus trees (Citrus): These trees prefer a sunny location in soil with a pH of 6-7.
  • Pineapples (Ananas comosus):  Coffee grounds provide an excellent source of nitrogen for pineapples. The soil pH level should be 5 to 6.5.
  • Blueberries (Vaccininium spp.):  A small, berry-like dark fruit that favors a sunny site and soil with a pH level of 4.5 to 5.5
  • Strawberries (Fragaria sp.): These well-known favorites thrive in sunny locations and soil with a pH level of 5.5 to 6.5. 
  • Avocado trees (Persea americana): These trees should be grown in a sunny but sheltered site in soil with a pH level of 5-7.
  • Mango trees (Mangifera indica): Mangos require high levels of nitrogen found in coffee grounds and grow best in soil with a pH level of 6-7.

Overflowing cup of whole coffee beans against a white background.

Vegetables

As we said before, coffee grounds are great for keeping the soil moist. Therefore, not all the plants will like coffee grounds in the soil.

  • Potatoes: (Solanum tuberosum): These starchy underground tubers prefer soil with a pH of 5-6.
  • Carrots (Daucus aorta subsp.sativus): A root vegetable, high in beta-carotene that prefers soil with a pH of 6 to 6.8.
  • Radishes (Raphanus sativus): This salad favorite prefers a soil with a pH of 6-7.
  • Eggplants/Aubergines (Solanum melongena): A very popular fruit also known as aubergines in Europe. They prefer a soil with a pH level of 6-7.
  • Parsley (Petroselinum crispum): Although widely used as a herb, parsley is actually a vegetable and both the leaf and roots can be used for culinary purposes. It requires soil with pH levels of 6-7.
  • Peppers: (Capsicum annuum): These colorful vegetables grow well in soil with a pH of 6 to 6.5.

Indoor House Plants

  • Daffodils (Narcissus): These bright and cheerful flowers that herald spring require soil with a constant pH of 6-7 to guarantee successful growth.
  • African violets (Streptocarpus): These lovely houseplants require soil with a constant pH of 6 to 6.5.
  • Nasturtiums (Tropaeolum): A favorite summer flowering plant that grows in slightly acidic to neutral soil with a pH level of 6-7. 

Tip: Nasturtium flowers and leaves are edible with a strong peppery taste. They are also a good source of vitamin C, calcium, magnesium and iron.

  • Snake plant (Sansevieria spp.): A low-maintenance plant that requires soil with a pH of 6-7.
  • African daisies (Osteospermums): These cheerful flowering plants will benefit from occasional applications of coffee grounds and prefer soil with a pH level of 5 to 5.5.
  • Christmas cactus (Schlumbergera spp.): This well-known succulent prefers soil with a pH of 5.5 to 6.5.
  • Jade plant (Crassula ovata): This is an easy-to-grow succulent houseplant that grows well in soil with a pH of 6 to 6.5.
  • Succulents (Succulents): These plants prefer a soil with a pH level of 6-7. They will benefit from an occasional, very light feed of coffee grounds.

What Plants Don’t Like Coffee Grounds

Not all plants like coffee grounds as they are slightly acidic, contain caffeine and are nitrogen-rich. A list of some plants that won’t thrive in these conditions include:

  • Geranium
  • Asparagus
  • Tomatoes
  • Salvia
  • Alkaline-loving trees like linden, ironwood, red chestnut, and arborvitae
  • Asparagus fern
  • Chinese mustard
  • Mediterranean herbs like lavender, thyme and rosemary
  • Orchids

What Plants Like Eggshells?

Eggshells can be more than just breakfast leftovers. They’re a valuable, free source of calcium carbonate that can significantly benefit your outdoor flowers, veggies, and fruit trees.

The following plants can be successfully grown using eggshells as a slow-release fertilizer.

Vegetables

  • Tomato (Solanum lycopersicum): The high calcium levels in eggshells help prevent blossom end rot. They prefer soil with a pH level of 6.5 to 8.5.
  • Bell Pepper (Capsicum annuum): Peppers also benefit from the high calcium found in eggshells and thrive in soil with a pH of 6 to 6.8.
  • Eggplants/Aubergine (Solanum melongena): This popular and versatile vegetable thrives in soil with a pH of 6-7.

House Plants

I don’t recommend using eggshells directly in contact with the soil for houseplants. Instead, eggshells should be placed at the bottom of the pot as part of the drainage materials. This is because the high calcium content in eggshells could overpower the soil volume in most pots used for house plants. In time, this will likely lower the pH of the soil, making it more alkaline and potentially harming your plants. However, if used as part of the drainage, your plants can still uptake a lower dose of calcium. The following plants are a few examples that will benefit from being planted this way. 

  • Mini Roses (Rosa): Mini roses benefit from the calcium and lime found in eggshells and prefer soil with a pH of 6 to 6.5.
  • Hydrangeas (Hydrangea): The calcium in eggshells raises the pH levels in your soil and, over time, turns the flower colour of large-leaf hydrangeas pink.
  • Spider plants (Chlorophytum comosum): These plants prefer a neutral pH soil level 6-7. Therefore, they will benefit from moderate applications of eggshell fertilizer.
  • Ferns (division Pteridophyta): It is best to use eggshells as drainage in the pots so the plants can benefit from nutrients. Don’t add eggshells to or on top of the soil, as these plants are particularly susceptible to direct contact. The soil should have a pH level of 5.5 to 7.
  • Ivy (Hedera): This well-known house plant grows well in soil with a pH of 6-7.

What Plants Don’t Like Eggshells

Eggshells can raise the soil pH, making it less acidic and more alkaline. Some plants will struggle or not even survive in these conditions. In addition, their nutrient uptake can be compromised, resulting in poor growth and susceptibility to pests and diseases. The following are examples of plants that thrive best in acidic soil and won’t benefit from the changes that eggshells can make to your soil:

  • Shrubs and Flowers: Azaleas, rhododendrons, Acers, geraniums, violets and large-leaf hydrangeas.
  • Fruits and Veggies: Blueberries, strawberries, radishes, parsnips, sweet potatoes and rhubarb.
  • Other Acid-loving Plants: Kale, cabbage, mountain laurel, and Pieris.

Note: This doesn’t necessarily mean you can’t grow acidic or alkaline plants together in the same border. It’s more about being aware of the effects of isolated applications of organic matter and how they affect the immediate growing environment of the plant and its close neighbours.

Benefits of Coffee Grounds As Fertilizer For Plants

Before discarding those used coffee grounds, learn how they can become a beneficial, budget-friendly fertilizer for your plants.

Nutrient content

Coffee grounds are rich in nitrogen but less so in potassium and phosphorus—three essential macronutrients that plants need for growth and development. They also contain traces of calcium, magnesium, iron, and manganese, all of which are essential to plants in varying degrees.

Soil amendment

When mixed into the soil, coffee grounds will significantly improve soil structure by increasing aeration and drainage. Dig at least four inches deep into the soil and let the worms do the rest over time. Coffee grounds also add organic matter, which promotes healthy microbial activity.

Note: Coffee grounds, if left on top of the soil, can create an impenetrable water barrier, which is not great, particularly if you have heavy clay soil like I do in my garden. You could end up with a top layer of soggy soil. Having said that, don’t be put off. In general, coffee grounds incorporated into the soil with other organic matter can significantly improve the structure and quality of soil in your garden.

Acidity adjustment

Used coffee grounds are only slightly acidic, which can benefit acid-loving plants like azaleas, hydrangeas, blueberries, and lilies by lowering the soil pH. However, this is a short-lived benefit, and other methods might be required. To significantly lower the pH, you might have to add sulfur, aluminum sulphate, or iron alongside applications of coffee grounds.

Slow-release fertilizer

As the coffee grounds break down over time, they provide a slow and steady release of nutrients to plants. However, these nutrients won’t be sufficient in quantity to benefit your plants in full. Therefore, you must apply other fertilizers to help make up the shortfall.

Pest/weed control

Coffee grounds contain caffeine and diterpenes, both of which are toxic to animals and insects. Many insects, such as ants, mosquitoes, flies, and spiders, are somewhat deterred by the smell of coffee. If made into a solution and sprayed directly onto plant leaves, coffee has a far better success rate on slugs. The smell of coffee also puts off cats and can deter them from entering and fouling in your yard or garden. However, remember that coffee is highly toxic to pet dogs if digested. 

Coffee grounds have allelopathic qualities, which means they contain chemicals that can suppress the growth and development of other plants nearby. Caffeine suppresses plant growth by tying up nitrogen in the soil. So, if applied wisely, coffee grounds are potentially a good weed suppressor.

However, caffeine can also suppress the growth of all plants, weeds or not! To avoid adverse outcomes, mix the coffee grounds with other organic materials, such as compost or leaf mold, before applying them as mulch.

Compost addition

Coffee grounds make an excellent “green” compost material, providing nitrogen when mixed with carbon-rich “brown” materials.

Vermicomposting

Earthworms can thrive on coffee grounds, making them a great addition to vermicomposting bins. Introduce them gradually so your worms can customize themselves.

How to Use Coffee Grounds As Fertilizer For Plants?

Direct Application

Direct application is best suited for small amounts of coffee grounds from a daily cup of coffee. 

  • Sprinkle a thin layer of used coffee grounds around the base of established plants.
  • Gently work the grounds into the top inch or so of soil to avoid forming a water-resistant layer.

Note: Coffee grounds are highly toxic to dogs if consumed. If you have a dog that is an indiscriminate eater, then use coffee grounds for composting instead of applying directly on the soil.

Composting

Composting is the best way to maximize the benefits of coffee grounds. Used grounds added to your compost pile will break down and create a richer, more balanced compost. Coffee grounds are considered a “green” composting material, so they must be mixed with “brown” materials, such as dried leaves or shredded paper to create a balanced compost.

In addition to using your own coffee grounds, you can also use grounds from local restaurants and cafes.

Liquid Fertilizer (“Coffee Tea”)

  • Add around 2 cups of used grounds to a 5-gallon bucket of water.
  • Steep for several hours or overnight.
  • Strain well to remove grounds.
  • Lightly water the base of your plants with the solution, taking care not to saturate the soil.

Whichever method you use, apply it only every six weeks during the growing season. This will be plenty, even for acid-loving plants.

Benefits of Eggshells As Fertilizer For Plants

Eggshells are packed with calcium carbonate, an essential nutrient for plants. When used as a fertilizer, they lower soil acidity.

Calcium content

Eggshells contain calcium, an essential nutrient for plant growth and development. Calcium helps strengthen cell walls, promote root growth, and improve overall plant health.

Soil amendment

Crushed eggshells can help improve soil structure by increasing aeration and drainage. They can also help raise the pH levels in acidic soils, making nutrients more available to plants.

Slow-release fertilizer

As eggshells break down over time, they provide a slow and steady release of nutrients to the plants, unlike quick-acting synthetic fertilizers.

Pest/slug deterrent

Crushed eggshells’ sharp, abrasive texture can help deter slugs, snails, and other pests from accessing plants. However, this method is only a short-term deterrent, and diatomaceous earth is more reliable in the long run.

Compost addition

Eggshells make a great “brown” carbon-rich material to add to compost piles, helping to balance the “green” nitrogen-rich materials.

Nutrient recycling

Using eggshells as fertilizer helps recycle nutrients and reduces waste, making it an environmentally-friendly option.

However, eggshells alone do not provide a complete, balanced fertilizer for plants and should be used in moderation as part of a broader soil amendment and fertilization strategy.

How To Prepare Eggshells As A Garden Fertilizer?

It is essential to wash eggshells to remove any residue and allow them to dry. This prevents unpleasant odors and reduces the risk of mold or bacteria growth.

The finer you crush the shells, the faster the nutrients will become available to your plants. You can do this by:

  • Hand: Crumbling pieces with your fingers.
  • Blender or Food Processor: For a finer powder.
  • Mortar and Pestle: For a coarse but consistent texture.

Methods of Application

Direct Sprinkle

  • Scatter crushed eggshells around the base of your plants.
  • Gently work them into the top layer of soil. This will significantly benefit plants that love calcium, like tomatoes and peppers. The high calcium content is well-known to help prevent blossom end rot in tomatoes.

Eggshell “Tea”

  • Soak crushed eggshells in a jar of water for a few days or up to a week.
  • Strain the liquid and use this calcium-rich water to feed your plants.

Compost Addition

Toss crushed eggshells into your compost pile. They’ll break down and contribute to a rich, balanced fertilizer.

Seed Starting Boost

  • Place a crushed eggshell half in the bottom of seed-starting pots. It provides a slow release of calcium for healthy seedlings.

Precautions While Using Coffee Grounds And Eggshells As Fertilizers

While coffee grounds and eggshells are free, full of nutrients and readily available, it’s essential to be mindful when using them on your plants.

Coffee Ground Cautions

Overuse can be an issue. Too much coffee applied directly to the soil can crust and create a barrier that prevents water absorption and air circulation to your plants. This will be more of a problem on heavy clay soil, resulting in soggy puddles. 

Caffeine is known to inhibit the development of seedlings and disrupt the growth of mature plants, potentially leading to their death. 

Again, don’t forget your pet dogs! If your dog consumes coffee grounds, you must seek urgent veterinary advice. Coffee grounds can cause symptoms of vomiting, accelerated heart rate, red eyes and diarrhea. 

Additionally, fresh coffee grounds can sometimes encourage mold growth if not dried out sufficiently. 

Overall, grounds from my daily coffee are enough when applied around the base of selected plants and mixed into the soil. I also use freebie bags of used coffee grounds from local cafes and restaurants for the compost heap, with a ratio of one-third coffee grounds, one-third brown material, and one-third grass clippings. Overall, it is best to use coffee grounds in moderation if applied directly or add them to the compost heap for a more balanced effect.

Eggshell Considerations

While eggshells offer calcium, not all plants thrive in high-calcium environments. If your soil is already alkaline, adding excessive eggshells could raise the pH too high, making it difficult for some plants to access nutrients.

To avoid this, check the pH level of your soil on a regular basis.

Also, washing or rinsing eggshells before use is vital to remove any bacteria that could cause fungal diseases on your plants.

Conclusion

Now that you know more about the pros and cons of using coffee grounds and eggshells, don’t be afraid to experiment! 

Observe how your plants respond, adjust your methods, and enjoy the journey of becoming an even better plant caretaker.

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