Coffee Grounds for Your Cannabis Garden

Stephen Andrews
12 Aug 2022

Grounds and chaff from home-roasted coffee beans can be reused for flower beds, vegetable plots, or Cannabis plants. This type of organic seed meal works as an excellent soil amendment. You can source it quickly if you use filter coffee. Or you can also approach a local coffee purveyor and help them out with waste management. Below, read more on the advantages of coffee grounds and how this natural fertilizer can aid your gardening efforts.

Benefits of Coffee Grounds

Spent coffee grounds is an inexpensive natural fertilizing solution. Grounds are rich in nitrogen content, one of the three essential macronutrients needed for cannabis plants to thrive. Used grounds may be dispensed directly onto the soil surface, around the base of the plant, or can be worked into the soil to offer time-released benefits. 

A seed meal such as spent coffee ground has pH values in the range of 5.8 and 6.2, which is acceptable for soil conditioning. If non-bleached paper coffee filters were used for preparing the coffee, the supplement might be composted as a whole without putting an additional strain on the environment. 

Spent coffee grounds will slightly raise the pH levels once added as a soil enricher. Using spent grounds, not freshly-ground coffee, is important, as caffeinated content may negatively affect the growing space. Fresh beans are also more acidic than spent ones. Fermented or rotting coffee grounds should also be avoided. 

The nitrogen contained in the spent coffee grounds may take some time to become available to plants. It needs to degrade from the organic fraction where it's locked. This practically means that the application of spent coffee grounds on the soil will have a slow, gradually-releasing effect. Plants will thus be exposed to a long-term nitrogen input. 

While coffee has a more significant percentage of nitrogen (this will slightly vary depending on the types of coffee beans), it also contains small amounts of other nutrients, including phosphorus, potassium, magnesium, copper, and calcium. The combination of nutrients is usually available in a healthy ratio. 

Just like with nitrogen, it will take time for some of the other macro- and micro-nutrients to become available to the plant, while some of it will immediately blend with the soil. Apart from cannabis, grounds are also great for tomatoes, carrots, lettuce, blueberries, radishes, etc. 

In addition, this kitchen waste product may also help deter certain garden pests. It can be used to create a snail and slug barrier. Don't anticipate a full pesticide effect from spent grounds, especially if an organic brand of coffee is used which does not contain any chemicals. But it can be useful with cats who might want to use your garden as a litter box since most cats detest the smell of coffee grounds. 

spent coffee grounds for cannabis gardening.

Five Ways to Use Coffee Grounds in the Garden

There are various ways how to fertilize your garden with spent coffee grounds. 

  1. Soil Amendment. Mix the used grounds six to eight inches into the soil. The grounds will supply both macro and micro-nutrients to your crops and help to condition and aerate the soil. 
  2. Side-Dressing Fertilizer. Feed the grounds directly to the plant. Spent coffee has a favorable carbon-to-nitrogen ratio, which is suitable for both plant and soil nutrition. 
  3. Composting. Apply with other plant materials. For example, the compost pile can be layered with 1/3 leaves, 1/3 fresh grass clippings, and 1/3 coffee grounds. Make sure to turn your compost regularly. 
  4. Worm Castings. If you have a worm bin, add coffee grounds once a week or so. Combine with kitchen scraps, fruits and vegetable peels. Worms will enjoy this tasty meal. 
  5. Foliar Spray. Prepare a spray solution by soaking about a half-pound of spent grounds in five gallons of water. Apply directly onto the plants. The spray is especially useful for the leaves undersides.

No matter how you process this type of kitchen waste, remember that it helps to condition the soil, it increases the soil structure and fecundity, and provides healthy nourishment for plants. 

Happy growing!

Stephen Andrews