Coffee grounds are often overlooked as a valuable addition to the compost pile. However, their texture and nutrient profile make them an excellent compost ingredient. When added appropriately, coffee grounds can improve soil structure, add beneficial nutrients, deter pests, and speed up the composting process. This article will explore the many benefits of composting coffee grounds and provide tips on how to use them effectively.
Improving Soil Structure
The small, moist particles of spent coffee grounds are great for improving the texture of soil. Their crumbly texture helps to break up compacted clays and increase air circulation in the soil. The grounds also retain moisture well, acting as a natural wetting agent in dry soils. As they decompose, the grounds leave tiny pores in the soil which improve drainage and oxygen flow to plant roots.
Over time, composted grounds will also feed beneficial microbes and earthworms that further enhance soil structure. The organic matter provided by the grounds increases the soil’s ability to hold nutrients and water. By composting coffee grounds, you can gradually improve the quality of garden beds and potted plants with each application.
Adding Nutrients
Used coffee grounds are considered a “green” compost ingredient, meaning they are rich in nitrogen. Nitrogen is a key nutrient required for lush vegetative growth. Coffee grounds typically contain around 2% nitrogen by volume, giving your compost a nutritional boost.
Along with nitrogen, the grounds contain other macro and micronutrients that plants need, like phosphorus, potassium, magnesium and copper. The grounds are also slightly acidic, with a pH around 6.5, which makes them useful for balancing more alkaline soils. Composting the grounds allows these nutrients to break down into plant-available forms that will amend the soil when applied.
Deterring Pests
As an added bonus, coffee grounds can help deter common garden pests like slugs and snails. These slimy creatures dislike crawling over the dry, gritty texture of coffee grounds. Sprinkling some fresh grounds around your seedlings is an organic way to create a sharp barrier that will keep slugs at bay.
The caffeine and slight acidity in the grounds are also thought to be unappetizing to snails. Spreading compost containing used coffee grounds around vulnerable plants can provide some protection from these pesky creatures. The effect doesn’t last long, so you’ll need to reapply the coffee barrier after heavy watering or rain.
Speeding Up Composting
Composting with coffee grounds can also decrease the time it takes to produce usable compost. Nitrogen-rich ingredients like coffee speed up the breakdown of carbon-heavy “browns” like dried leaves, wood chips or cardboard. The grounds encourage the growth and reproduction of beneficial composting microbes.
With the right carbon to nitrogen (C:N) ratio, these microbes thrive and rapidly digest the organic matter. Most compost experts recommend mixing one part fresh coffee grounds with two parts browns by volume to get your C:N ratio in the optimal range. The increased biological activity means your compost pile will heat up quickly and be ready for use sooner.
How to Compost Coffee Grounds
Composting with coffee grounds is very straightforward. Here are some tips for adding spent coffee grounds to your compost:
- Collect the wet grounds in a container rather than putting them straight into your compost bin. Allow them to dry for a day or two first. Fresh wet grounds can clump together and restrict airflow in the pile.
- Mix the dried grounds with 2-3 times as much browns like dry leaves, straw or wood shavings. This will prevent the grounds from compacting and maintains an ideal C:N ratio.
- Bury the coffee grounds in the center of your compost pile, at least 10 inches deep. This prevents them from drying out. Cover with more brown materials.
- Water the pile as needed to keep it moist but not saturated. Excessive moisture will make the compost anaerobic and slow down decomposition.
- Give the pile an occasional turn or stir to incorporate more oxygen into the interior. Coffee grounds can settle and compact over time.
- In 2-4 months, the grounds should be fully broken down into rich, crumbly compost, ready for the garden.
Using Composted Coffee Grounds in the Garden
Finished compost containing coffee grounds has many uses around the garden. Here are some of the best ways to use composted coffee grounds:
As a Nutrient-Rich Soil Amendment
- Mix 1-2 inches of composted coffee grounds into garden beds and potting mixes. This adds organic matter and nutrients to improve soil quality over time.
As Mulch for Plant Beds
- Spread a 1/4 – 1/2 inch layer of compost made with coffee grounds around annuals and perennials. The compost will slowly break down, feeding plants while suppressing weeds.
When Planting Trees, Shrubs and Perennials
- Add a few shovelfuls of coffee-enriched compost into each planting hole when transplanting new plants. This gives their roots an extra dose of nutrients for establishment.
For Potted Houseplants and Container Gardens
- Use up to 30% composted coffee grounds mixed into potting soil for houseplants. The compost helps aerate soilless mixes while providing a slow-release fertilizer.
As a Nutritious Mulch for Acid-Loving Plants
- Plants like azaleas, blueberries and hydrangeas appreciate compost made with acidic coffee grounds. Apply 1-2 inches around their root zones as mulch.
To Boost the Nutrients in Tired Garden Soils
- To rejuvenate old garden beds, apply a thicker layer of composted coffee grounds, up to 4 inches. Work it into the top 6 inches of soil to revitalize.
Choosing the Right Plants
While most plants thrive with the addition of composted coffee grounds, some species are particularly well-suited to the acidic pH and nutritional content of coffee-amended soil. Consider using composted coffee around these coffee-loving plants:
- Azaleas and rhododendrons: These flowering shrubs need acidic soil, so coffee grounds are ideal. Work compost into beds before planting, and use as mulch.
- Hydrangeas: For gorgeous blue blooms, hydrangeas rely on acidic soil. Coffee grounds can provide this while encouraging healthy growth.
- Blueberries and cranberries: These fruits grow best with coffee grounds compost maintaining the preferred soil pH below 5.5.
- Camellias: Beautiful camellias flourish when planted with acidic coffee compost used as a soil amendment and refreshing mulch.
- Roses: Composted grounds provide roses with steady nitrogen along with organic matter to produce incredible blooms.
- Tomatoes and peppers: These vegetables appreciate nitrogen, so a bit of coffee grounds in compost is beneficial, especially when first planted.
Troubleshooting Coffee Ground Composting
Composting with coffee grounds is quite simple, but occasionally some issues can arise:
Problem: The compost pile doesn’t seem to be heating up.
Solution: The carbon to nitrogen ratio may be off. Try mixing in more dried “brown” materials like leaves to provide additional carbon. Turning the pile can also introduce more oxygen to jump start the microbes.
Problem: There’s a strong, unpleasant ammonia smell from the compost.
Solution: Too much nitrogen from the coffee grounds causes excess ammonia production. Add more carbon-rich ingredients like sawdust or paper, and turn the pile to release the ammonia gas.
Problem: Mold is growing on top of the coffee grounds.
Solution: The grounds are staying too wet. Allow them to dry fully before composting. Mix the grounds into the center of the pile, not on top where moisture can accumulate.
Problem: The compost is clumping rather than breaking down.
Solution: Coffee grounds can compact tightly. Loosen up the pile by turning it, and add coarse materials like straw or corn cobs to improve aeration.
Conclusion
Composting with coffee grounds, when done properly, provides multiple benefits in the garden. The grounds enhance soil structure, add valuable nutrients, help deter pests, and speed up the composting process. While fresh coffee grounds may have downsides like compacting or odor, once aged and composted they are an excellent organic amendment. By recycling this common kitchen “waste” as garden compost, we can reduce landfill contributions while growing healthier, more abundant plants.