Coffee grounds have long been used as plant fertilizer for turf grass and other plants grown for their green leaves. The nitrogen in the leftover coffee is said to give the lawn a boost of nitrogen, causing it to “green-up”. But are coffee grounds actually good for grass?
Yes, you can use coffee grounds for grass fertilizer, on one condition – the coffee grounds must be composted prior to use on the lawn. Coffee grounds do indeed supply essential nitrogen to the lawn, but the raw grounds may actually harm the health of the lawn soil. Put coffee grounds through the compost with shredded fall leaves or other similar dry material and then use the finished compost as a top-dressing feeding for the grass.
There are a few important processes to follow to ensure your lawn is getting the benefit of nitrogen from the coffee grounds without any negative effects. Read on to learn exactly how to use coffee grounds for turf grass fertilizer and as plant food for any plant grown for its green foliage.
Why Not to Use Raw Coffee Grounds on the Lawn
Contrary to popular belief, raw coffee grounds should not be applied directly to lawn grass or other foliage plants. While the earthworms will certainly feast on the grounds and help improve soil structure, the chemical makeup of the raw coffee can harm other beneficial organisms in the soil. Any benefit from the coffee’s nitrogen can be lost completely since nitrogen from plant matter must be processed by soil microorganisms before plants can absorb it.
Grass depends on soil micro-organisms to transform the nitrogen in coffee grounds into a chemical form that it can absorb. These soil microorganisms depend on a healthy soil ecosystem. Raw coffee can throw the soil ecosystem completely out of balance, meaning that adding raw grounds to the lawn can cause more trouble than its worth. Composting the raw coffee grounds allows you to get the nutrient benefit without risking the health of creatures in the soil.
The addition of raw coffee grounds to plants has actually been known to stunt growth instead of encourage it:
“Growth of crops such as Chinese mustard (Brassica juncea), komatsuna (Brassica campestris) and Italian ryegrass (Lolium multiflorum) were all inhibited by coffee grounds, as was that of ornamentals including inch plant (Tradescantia albiflora), geranium, and asparagus fern. One investigator speculated that toxic substances released from decomposing coffee grounds were responsible for their inhibitory effect.”Myths, Miracles…or Marketing? Coffee grounds — will they perk up plants?, Linda Chalker-Scott, Ph.D., Master Gardener, Extension Urban Horticulturist and Associate Professor, Washington State University
Coffee grounds can also become quite compacted when applied directly the the lawn. Even light foot traffic and lawn maintenance can compress the raw grounds into a crust layer on top of the soil, impeding both air movement and moisture flow. Since the soil balance of water and oxygen is vital to great turf grass, it is prudent to avoid creating any kind of barrier crust on top of the soil surface.
How to Use Coffee Grounds for Grass Fertilizer
To use coffee grounds for grass fertilizer, put them through the compost first with some nice dry yard waste such as shredded fall leaves. The dry “brown” material is rich in carbon and will help to balance out the nitrogen-rich coffee grounds. Homemade compost for your lawn top-dressing can include 10-20 percent coffee grounds by volume:
“Percentages of 10 to 20 percent of total compost volume have been reported as optimal for compost quality and effectiveness, while over 30 percent can be detrimental.”Myths, Miracles…or Marketing? Coffee grounds — will they perk up plants?, Linda Chalker-Scott, Ph.D., Master Gardener, Extension Urban Horticulturist and Associate Professor, Washington State University
Sprinkle on the coffee grounds in thin layers in the compost heap between layers of shredded deciduous leaves. Moisten each layer with water as you go. The moisture is vital for efficient decomposition of the coffee grounds into stable nitrogen-rich lawn fertilizer. Here are some great composters for turning coffee grounds into plant food:
- Jora JK270 Large-Sized Dual-Chamber Steel Compost Tumbler (Sealed, Insulated)
- Aerobin 400 Insulated Composter - 15 Cubic Foot (112 Gallon) Compost Bin
- Worm Factory 360 Composter
If you’re still worried about the acidity of the coffee grounds, you can buffer the pH by adding some alkaline material such as limestone or ashes from burnt wood. Add the alkaline material into the compost pile by sprinkling it on with the coffee grounds or by premixing the basic material into the acidic grounds as follows:
“…the coffee grounds they’ve tested have also had a very high residual acidity; so high he recommends adding a cup of agricultural lime to every ten pounds of grounds BEFORE you add them to your compost pile. (High-quality hardwood ashes could be used instead of the lime, and would add more nutrients to the mix than the lime would.)”Using Coffee Grounds Correctly, by Mike McGrath, You Bet Your Garden, Gardens Alive
A feeding of coffee-leaf compost on the lawn in the spring and fall should be more than enough to feed your turf grass with an ample supply of nitrogen. You’ll also be supplying the lawn with slow-release forms of other essential plant nutrients:
“But what do your coffeepot’s leftovers really add to the soil? To find out, Sunset sent a batch of Starbucks’ used coffee grounds ― the company gives them away for free ― to a soil lab for analysis. Turns out the grounds provide generous amounts of phosphorus, potassium, magnesium, and copper. They also release nitrogen into the soil as they degrade. And they’re slightly acidic ― a boon in the Western climate.”Add Used Coffee Grounds to Your Garden Soil and Get Amazing Results, Sunset Magazine
Why Composted Coffee Grounds Are Good For Grass
Composted coffee grounds are good for grass because they are high in nitrogen. Brewed grounds can contain quite a high amount of nitrogen in comparison to the plant matter around most residential yards. The grounds also contain other essential plant nutrients, including micronutrients that are vital to healthy turf grass. Coffee grounds can greatly enrich your compost pile, releasing their nutrients and even keeping away pests.
“Nitrogen-rich proteins needed for seed germination and growth comprise over 10% of coffee grounds. In fact, the carbon-to-nitrogen ratio of coffee grounds can be as low as 11:1, an ideal ratio for plant and soil nutrition.”Myths, Miracles…or Marketing? Coffee grounds — will they perk up plants?, Linda Chalker-Scott, Ph.D., Master Gardener, Extension Urban Horticulturist and Associate Professor, Washington State University
Coffee grounds also attract earthworms who eat the grounds as food. While earthworms can make lumps in turf grass, their presence indicates a healthy soil ecosystem and they should not be discouraged. Encourage the earthworms to feast on the raw grounds in the compost instead of directly on the lawn. Keeping the worm buffet party in the compost heap leads to fewer worm lumps on your lawn.
Another reason that coffee grounds are great for grass is that they can be used instead of synthetic chemical fertilizer. Conventional lawn fertilizers are made with nitrogen that’s synthesized from natural gas. Use of fossil-fuel derived fertilizer isn’t sustainable and isn’t necessary (especially if you’ve got lovely coffee grounds around!). Not only are the coffee grounds not made from petroleum, they’re also essentially free.
Coffee grounds would otherwise be thrown out, so by using it for the benefit of your lawn you save money on store-bought lawn fertilizer. Finding ways to repurpose your household waste appropriately it a great way to save money and help the environment. The slow-release form of the composted grounds makes them less likely to contaminate both groundwater and surface water. Lastly, another benefit over many store-bought fertilizers is that the coffee grounds also create beneficial humic soil components as they decay.
“The nitrogen, phosphorus, potassium “guaranteed analyses” would be as follows for the coffee grounds:
– Nitrogen: 2.28 percent
– Phosphorus: 0.06 percent
– Potassium: 0.6 percent”Add Used Coffee Grounds to Your Garden Soil and Get Amazing Results, Sunset Magazine
That’s a fairly ideal NPK for an organic lawn fertilizer!
Using Coffee Grounds as Organic Lawn Fertilizer
So coffee grounds can be great on the lawn as long as they are processed through the compost first to provide a bit of chemical buffering prior to direct contact with the turf grass and underlying soil. Always compost your grounds with a healthy volume of brown yard waste prior to using the coffee grounds for grass fertilizer!