There are a lot of old wife tales about different products that you can add to your garden compost to improve your soil and Coffee Grounds normally get high regard by small gardeners that make their own compost. However there are some issues that can arise from using coffee grounds in your compost and before you get carried away you should do some research on what properties they contribute to your soil.
First coffee grounds should not be looked at as some type of Miracle additive. If they provided such a dramatic effect on plants then garden centers would be selling them to you by the bag. Since they don’t then you have to understand that Coffee Grounds are just basic filler material for your compost. They are adding bulk organic material which you could find in most plant materials. If you are really looking for something that will improve the organic material in your soil quickly and at a low cost then you should probably look at something like peet moss which can be purchased in bulk and tilled into your soil.
Using Coffee Grounds In Soil PH Levels And Nutrients
Normally used coffee grounds should have a 6.4 to 6.8 PH Level which is very close to neutral. Unlike other materials from your yard like grass clippings, pine needles or leaves you can expect that used coffee grounds will not have much effect on the PH Levels in your soil which is a good thing for most plants. On the other hand studies have shown that you can not always count on the PH Level to be neutral and it can vary anywhere from a 4.5 to a 8.5 depending on the manufacturer and coffee type. For that reason if you were not just adding your average 1/4 cup of used grounds per day to a large amount of compost and if you were collecting grounds from maybe a local coffee shop then you would definitely want to test the PH levels before you added them to your compost.
Nutrients found in coffee grounds are just like any other organic material. They are normally a decent source of nitrogen which is beneficial to most plants however the amount of nitrogen will again depend on the variety of coffee and how it is processed. Testing nitrogen levels is not an easy thing for the average gardener and it will normally require a soil test by a lab which is not reasonable for most small gardeners. For that reason you can place them in the Generally Good category when it comes to providing nitrogen for your plants.
Somewhat Myth Coffee Grounds Improve Microorganisms In Soil
Because Coffee Grounds are an organic material they can be consumed by microorganisms in your garden and this is a good thing but they are no better than any other organic material when it comes to feeding these microorganisms.
Coffee Grounds In Compost Can Stunt Plant Growth
There have been studies that show that the common coffee plant will drop its leaves and beans and the caffeine in the soil around the plant becomes a natural herbicide which allows the coffee plant to grow easier without competition.
In addition tests have shown that when there are high levels of coffee grounds of 25% that the germination of lettuce seeds can be stunted. For this reason it is suggested that you never use coffee grounds in compost that you expect to use for starter soil. This would be true if you are applying it to garden beds where you direct sew your seeds as much as seedling flats.
Final Note
Although you don’t need to throw away your coffee grounds and you can use them in your garden compost the myths around it being a great supplemental product are far from true. In small amounts it will act like any other soil amendment by providing organic material that can be broken down by microorganisms that will release some nitrogen into your soil.
However at high concentrations the use of Coffee Grounds has been shown to stunt the growth of both seedlings and plants as they mature. For this reason it is probably better to stick with other sources of compost building materials.
So just like you might not throw away those outer cabbage leaves or broccoli stems and you add them to your compost you can also add the days coffee grounds just like any other plant material but don’t get carried away and expect more than they are.