A cup of freshly brewed coffee gives people worldwide a morning boost. But did you know that the coffee grounds you typically discard as “kitchen waste” can do wonders for your plants? When used correctly, various studies prove the positive impacts of coffee grounds on plants of all sizes and types. 

But what do coffee grounds do for plants? In short, they replenish nutrient-depleted soil, contribute to healthy plant growth, suppress diseases, and improve the texture of potting mixes.  

Let’s explore the dos and don'ts of using coffee grounds as a fertilizer in more detail to help you get the most out of your indoor or outdoor garden. 

Are Coffee Grounds Good for Plants?

Yes, coffee grounds are useful to plants, but it's important to use spent coffee grounds rather than fresh ones. Fresh coffee grounds may be high in nutrients but are highly acidic and rich in harmful caffeine, which can burn your plant’s roots. Used coffee grounds have a neutral pH, making them a safer alternative. 

Coming to the benefits, coffee grounds can be used as a natural fertilizer to replenish old soil with fresh nutrients. They also help improve soil structure by enhancing drainage, airflow, and moisture retention. In addition, coffee grounds deter pests like slugs, snails, wasps, fleas, and ants, keeping your indoor or outdoor garden insect-free. 

What Nutrients Are Coffee Grounds High In?

Coffee grounds, used or fresh, are high in nitrogen, potassium, and phosphorus. In addition, coffee contains trace micronutrients like boron, copper, iron, and zinc. While the quantity and proportions of these nutrients may vary, coffee grounds still make an ideal natural fertilizer for many houseplants.

What Indoor Plants Like Coffee Grounds?

Some indoor plants benefit from coffee grounds because of their high NPK content and ability to improve soil structure for optimal growth. Plants that are “nutrient-hungry” and prefer slightly acidic soil do well with used coffee grounds added to the topsoil. 

For instance, Snake Plants, Philodendrons, the Peace Lily, Pothos, Palms, the Jade Plant, and the Money Tree are coffee-loving plants. It’s important to note that mixing too much coffee grounds in the potting medium may affect its drainage, so use them sparingly over the soil for exotic plants like Sansevieria. 

What Plants Don’t Like Coffee Grounds?

Some plants react negatively to coffee grounds mixed in the soil. This may change the texture of the potting mix, making it retain excess moisture, which can lead to root rot, pest infestation, etc. For this reason, you should refrain from feeding coffee grounds to plants that need well-draining soil to grow. 

While used coffee grounds have a neutral pH of 6.5-6.8, they should still be avoided for plants like Ferns and herbs (Rosemary and Lavender) that thrive in neutral to alkaline conditions. Furthermore, drought-resistant plants that thrive in sandy soil, such as most true succulents and cactus plants also fall under this category. 

How to Use Coffee Grounds as Fertilizer

If you're wondering how to use coffee grounds for plants, you’ll find multiple  ways to incorporate this common kitchen waste item into your plant care routine:

• Add the used grounds to your compost: Add the used coffee grounds to your compost, and once ready, mix a small amount of it with the potting soil. However, ensure the coffee grounds used make up only 10-20% of the total composite mixture by weight. This will maintain the right balance of nutrients and soil structure. 
• Create a liquid fertilizer with used coffee grounds: Mix 1-2 cups of leftover coffee grounds with 5 gallons of water. Let this mixture sit for a few nights before straining it through cheesecloth. Your coffee water for plants is ready for use; water and fertilize your green companions simultaneously.
• Sparingly sprinkle coffee grounds on top of the soil: Directly sprinkle spent coffee grounds over the soil to nourish it with all three essential nutrients - nitrogen, phosphorus, and potassium. Don't sprinkle too many dried coffee grounds; otherwise, they will block water absorption and airflow by making a thick layer over the soil. 
• Apply as mulch on top of the soil: Combine used coffee grounds with shredded dry leaves, straw, tree bark, and grass clippings. Apply a thin layer of this mixture around the base of your outdoor plants in the garden to shoo insects, retain moisture, and keep roots cool in hot weather. 

How to Prepare Coffee Grounds for Plants

Preparing the coffee grounds for plants properly is essential before using them. Firstly, allow the coffee grounds to dry completely before adding them to the soil. Spread them on baking paper or a tray for a few days to help them dry faster. This is an important step as dry grounds are less likely to clump together, reducing the risk of mold or moisture retention when mixed into the soil or compost. 

How Often Should I Put Coffee Grounds on Plants?

You can fertilize your plants with coffee grounds once or twice in the growing season (spring and summer). Adding coffee grounds more frequently may affect the soil’s structure and pH, leading to root rot, leaf issues, and turning the foliage yellow, or brown at the tips. This applies to both houseplants and outdoor plants. 

Can I Put Coffee Grounds Directly on Plant Soil?

Yes, you can put coffee grounds directly over the plant soil, but it's important to do so in moderation. Adding a thin layer prevents compaction which can result in water-absorption and airflow issues. Mix the grounds into the soil or compost them first for best results,

Coffee Grounds for Plants: FAQs

Q: Do coffee grounds change the soil pH level?

A: Used coffee grounds have a neutral pH of around 6.5-6.8, so theoretically they shouldn’t affect the soil’s pH level too much. On the other hand, fresh coffee grounds that haven't been brewed yet are highly acidic and can negatively impact your houseplants by burning their root system.  

Q: What kind of coffee should I use as fertilizer for my houseplants?

A: Use organic coffee, free of pesticides whenever possible. Dry the used coffee grounds first as they have already lost most of their acidity after brewing, making them a better and safer option for your plant’s health. Fresh coffee grounds are too acidic and contain more harmful caffeine, which isn't good for most houseplants. 

Q: What are the disadvantages of coffee grounds as fertilizer?

A: Using coffee grounds as fertilizer has its drawbacks in some cases. Coffee grounds often contain plant-toxic compounds that could lead to poorer growth in plants. Coffee grounds can also increase water retention in soil resulting in root rot. Furthermore, sprinkling a thick layer over the soil surface can block the water and air from reaching the plant’s roots. Coffee grounds might attract pests like fruit flies, too. 

Q: Can coffee grounds be used as an insecticide for plants?

A: Yes, coffee grounds can be used as an insecticide against pests like slugs, snails, and ants. However, coffee grounds aren’t effective against all insects, so consider them a complementary pest control option rather than a full-fledged solution. 

Q: What is the NPK content of coffee grounds?

A: Organic coffee grounds have an NPK (nitrogen, phosphorus, and potassium) content at a ratio of 2.1:0.3:0.3. Other trace elements include copper, boron, zinc, and iron, which are also beneficial to plants’ growth

Conclusion

Coffee grounds can be incorporated into your garden or indoor plant care routine but you should know how to use them correctly. They enrich the soil with essential nutrients, improve overall soil structure, increase water retention, and deter pests. However, it’s important to use them in moderation and understand which plants benefit from them. Not all plants react positively to coffee grounds! 

By following the tips in this guide, such as mixing grounds into the soil or creating a compost blend, you can maximize the benefits without harming your plants. Remember, balance is key to promoting healthy plant growth!