Are Coffee Grounds Good for Plants?

With a little extra work and foresight, you can compost your coffee at home to enrich your indoor plants. Many local coffee shops are happy to let you take their grounds as well. Most prefer to see waste go to use, especially in a way that can enrich a home. 

Most experts advise against directly dumping your coffee grounds on your plants. While you can dump coffee grounds directly on your plants (and some people get away with it without problems), it can potentially cause issues including:

• Fungal/mold overgrowth on the top of the soil, over your roots

  Fungal mold can lead to disease and decline of your plant’s health.

• Coffee Can Attract Unwanted Pests

  While some insects are put off by the smell of coffee, others will flock to your plant and cause damage. Do your research to see which plant pests you want to keep away.

• Moisture Retention, Which Could Cause Root Rot on Some Plants

  Overwatering is one of the most common problems with houseplant owners. When the water won’t drain or evaporate, the problems with overwatering are increased.

• Can Slow the Growth of Your Plant

  Some studies suggest that the caffeine from the grounds can stunt the growth of seedlings or young plants.

These issues are caused because of the consistency of your coffee grounds. They are course and easily clump together and become impacted. This creates a layer on top of your soil that prevents the evaporation of water. It also makes it difficult for air to reach the soil. 

To avoid these issues, compost your coffee grounds before using them on your plants. 

Note: If you are currently potting a plant (or re-potting it in a larger container), you can sometimes mix coffee grounds with your soil, which will release nutrients over time as the coffee decomposes. When mixed, the grounds don’t have the same impact as they do when placed on top of the soil. Consider using perlite or sand to further help the moisture drain. 

Are Coffee Grounds Too Acidic for Your Soil?

Some plants are very sensitive to acidic soil. While coffee grounds will lose varying amounts of acidity while they decompose, if you are worried about the pH balance of your soil, avoid using them. 

Coffee grounds are rich in carbon and nitrogen (between 10-20 parts carbon to 1 part nitrogen), two of the important nutrients for houseplants. Aim to have 20% of your compost be made up of coffee grounds. The other 80% should be made of other organic material that will develop into richer compost. Worms and microorganisms are attracted to the coffee and will help your compost develop more quickly. 

The NPK (Nitrogen – Phosphorus – Potassium) count on “home-made” compost containing coffee will vary, but will generally range around 2-.3-.3. Add it to other composts and fertilizers to change the balance for your houseplants. 

Periodically add a thin layer (no more than 1 inch or 2.5 cm) of the compost to the top of your plants. Many experts recommend that you fertilize your plants every fourth watering. Watch your plant carefully to see how it reacts to the compost. Add a little less water than you usually would when you compost to ensure that your plant still drains properly. Adjust future fertilization according to what you observe. 

You can also mix the compost into the soil when you repot your plants into larger containers.

Why Should You Use Coffee Grounds as Part of Your Compost?

Coffee grounds are high in carbon, nitrogen, and other nutrients that your houseplants need to thrive. They are a kitchen waste that most people discard, so using them in your compost is free. It is an efficient way of reducing your personal waste while helping your plants grow. Supplementing store-bought fertilizer with your own compost will decrease the amount of fertilizer you use.

A better way to use your compost on your houseplants is through the compost tea method. To create compost tea, complete the following steps: 

• Mix finished compost in a 1:1 ratio with water and let it sit for a day or two (Alternatively, you can add your coffee grounds directly to the water and let it sit and seep for 10-14 days).
• Use a strainer to separate the liquid and solids and discard the solids (or sprinkle it over your outside garden).
• Mix the liquid “tea” with enough water to water your houseplants correctly. 
• Use this method every fourth watering. 

This method will allow your plants to get the beneficial nutrients and bacteria from the coffee without the worry that the grounds will cause issues. Again, watch your plants for signs of too much nitrogen (such as discoloration on leaves) after using this method. Adjust future tea-waterings as necessary.

Note: you can use the brewed coffee in a similar way, but don’t use coffee that has added milk or creamer.