Hi and welcome to Taiga Bonzai, in this short post we discuss the arguments surrounding the use of coffee as a fertilizer or mulch in soil mediums.
Introduction – in 1958 coffee was added to the list of foods and beverages recognized by the World Health Organization (WHO) as safe for human health. This ended many years of debates regarding the effects of coffee on human health. Recent studies show that coffee alleviates asthma bouts, allergies and prevents tooth decay it also activates burning of fats in the body, replenishes potassium deficit and contributes to the improvement of the cardiovascular function. Coffee is a powerful source of antioxidants.
The main biologically active component of coffee is organic alkaloid caffeine that is found in various quantities in more than a hundred plants. However, only coffee, cocoa berries, kola nuts contain quite significant amounts of caffeine. Numerous studies suggest that due to its caffeine content coffee increases the speed of human reaction, aids concentration, associative thinking, relieves drowsiness and improves mood. Arguably it all depends the amount of consumption.
Coffee in whatever form ground, roasted or granulated is acidic, but when processed into a beverage the grounds lose their acidity hence they become neutral although there may be a small percentage of acidity remaining. Coffee grounds make good fertilizer because they contain several key nutrients required for plant growth. They also attract worms and decrease the concentrations of heavy metals in the soil. Coffee houses often give spent coffee grounds to horticulturists, because they are a waste product a free available resource.
Nonetheless, there are differences of opinion some horticulturists argue that coffee grounds should not be used as they have a disastrous effects on certain plants for example. Geranium, asparagus fern, Chinese mustard, Italian ryegrass and pin oak. The probable cause for these negative results is due to the amount of coffee grounds used either as a mulch or mixed in the actual soil medium; but the question is how much to use. This Kengai (cascade) Juniper (below) gets a small sprinkle (half a teaspoon) of unprocessed coffee grounds on the top of the soil medium each spring, which slowly releases the acidity when watered.
Spent or waste coffee grounds if making ericaceous soil can be added to the mix, but in small quantities and preferably dried out prior to combining all the ingredients together. It is important to create a correct balance too much of a particular ingredient can do more harm than good. Because it can decrease the availability of plant nutrients including phosphorus and molybdenum, that increases the availability of some elements to toxic levels, particularly aluminium and manganese. Essential plant nutrients can also be leached below the rooting zone.
According to the Oregon State University the acid in coffee beans is water soluble and bad for plants because they are allelopathic, which can reduce the growth of other nearby plants that compete for minerals and water. It is also stated that earthworms can perish when in contact with Caffeine. However, others argue that caffeine in processed coffee ends up in the cup not in the spent grounds that become almost neutral with a pH of 6.5 to 6.8 which is close to the midway point of 7 on the pH scale. (Shown below)
As stated we use coffee grounds both unprocessed and processed on our bonsai and there have not been any problems to date. Nonetheless, there exist many written articles on the subject, which can be found on the world wide web, whether you wish to try spent coffee grounds as a fertilizer or mulch that is your decision.
Since we returned from our break in March (17th) 2021 with article 46 “The road is long with many a winding turn” we have posted 45 articles non-stop however, we are forced to take a break due to the fact that we are moving to a new location. This task is going to a real headache considering what we have accumulated after 20 years in one place. We hope to be up and running again mid spring, until next time, BW, Nik.