There are both advantages and disadvantages to applying coffee grounds on plants. While coffee grounds have nutrients that might help plants grow, they also have toxins that can stop some plants from growing.

Depending on how they are handled, coffee grounds can have a variety of effects on plants. Read on to find out if you really should be adding your used coffee grounds to your plants, or if you are better off tossing them into the recycle bin or trash.

Benefits Of Coffee Grounds On Plants

It is crucial to note up front that we are talking about using used coffee grounds—that is, grounds that have already been used to create coffee. This is crucial because brewed coffee, used coffee grounds, and new coffee grounds all have unique qualities. For instance, freshly brewed coffee is very acidic, whereas used coffee grounds are not.

Coffee Grounds Contain Nutrients

Coffee grounds that are left over after brewing contain a mixture of proteins, lipids, and carbs that the water did not extract. Nitrogen-rich proteins make up about 10% of the spent grounds—and plants use a lot of nitrogen. Together with calcium, iron, magnesium, zinc, and trace amounts of phosphorous, coffee grounds also include potassium and trace amounts of phosphorus.

Coffee Grounds Contribute To Healthy Soil 

Despite the fact that coffee grounds contain healthy elements, plants cannot use those nutrients directly from the grounds. The coffee grounds must first decompose naturally or through composting. These procedures allow soil bacteria to convert the essential nutrients included in coffee grinds and other organic components into substances that plants can utilise.

Composted coffee grounds can add organic matter to the soil, enhancing soil structure and facilitating water and air circulation through the soil profile.

Disease Suppression 

Research has shown that adding coffee grounds to a compost mixture inhibited the growth of some disease-causing organisms in tests with vegetable crops. Common fungal rot and wilts including Fusarium, Pythium, and Sclerotinia species were among the diseases that were affected. The prevention of disease in houseplants or garden ornamental plants has not been investigated.

Some Of The Challenges Of Using Coffee Grounds On Plants

Studies have shown that there are negative effects connected with utilising coffee grounds on plants in addition to any potential advantages. While the majority of these difficulties have only been seen in crop or landscape plants, they might also be present in indoor plants.

A Reduction In Plant Growth And Other Issues

While we may rejoice that weed growth was reduced as a consequence of a study looking at the effects of directly applying used coffee grounds to several plants in field experiments. unfortunately, plant growth was also inhibited. Similar effects were observed in another study on geranium, asparagus fern, and the common houseplant spiderwort (Tradescantia albiflora). Sadly, only few houseplants have undergone actual testing.

Fresh coffee grounds are indisputably phytotoxic (toxic to plants), thus using them as a mulch or amendment is not advised. The fact that finely chopped coffee grounds have a tendency to compress, forming a moisture barrier across the soil surface, is another reason to avoid direct application of coffee grounds. This might promote fugal development and hinder root airflow.

One shouldn’t expect that the pH of decomposing coffee grounds will always or ever be acidic because it is not a fixed value. Don’t therefore expect that coffee grounds will produce an acidic compost. Research examining how used coffee grounds affect soil pH have revealed that the pH is not consistently lowered. In fact, from one study to the next, the final pH of composted coffee grounds varied greatly.

How To Safely Use Coffee Grounds On Houseplants

Making fertiliser tea from composted coffee grounds and using it to feed indoor plants is a common suggestion. Yet, there is no scientific evidence in favour of using compost tea for anything. Although compost is fantastic, the water that percolates through it only serves as a very weak fertiliser.

The best results come from utilising completed compost directly as a soil supplement or mulch for indoor plants, much like in the garden. Adding a thin layer of finished compost on top of the potting soil in containers is an easy method to use it. This is a good approach to add more compost in between repotting plants and can be done once to twice a year. This approach doesn’t yield the same results.

Because the composted material is lighter, it does not clump in the same way, and allows for the easy circulation of air and water.

Another approach is to incorporate the finished compost into the potting mixture. After composting, you can safely add the mulch to potting soil to promote soil health and plant growth. Compost improves drainage, aeration, and soil nutrient retention by loosening soils, reducing compaction, and enhancing drainage. Up to 30% finished compost can be added to potting mixtures as an amendment.

Which Houseplants Benefit From Composted Coffee Grounds?

About which plants benefit from coffee grounds and which do not, there are several lists available. Nevertheless, a lot of these lists are based on the incorrect premise that used coffee grounds are acidic, which isn’t true, especially after composting.

The list is based on plants that favour acidity at or below pH neutral (7.0) and/or can handle it.

  • African violet (Saintpaulia spp.)
  • Aloe vera (Aloe barbadensis)
  • Azaleas (Rhododendron spp.)
  • Bromeliads (Bromeliaceae)
  • Christmas cactus (Schlumbergera spp.)
  • Golden pothos (Epipremnum aureum)
  • Jade (Crassula ovata)
  • Peace Lily (Spathiphyllum spp.)
  • Persian cyclamen (Cyclamen persicum)
  • Philodendron (Philodendron bipinnatifidum)
  • Roses, miniature (Rosa chinensis minima)
  • Snake plant (Sansevieria trifasciata)
  • Spider plant (Chlorophytum comosum)

We hope you found this article helpful. Personally we would suggest composting your used coffee grounds before using it on your plants to ensure that it does more good than harm. Please do share your thoughts and experience with us, as we would love to improve our plant game!