Growing Science


With the rising atmospheric carbon levels, it is important to find ways to reduce our carbon footprint.  One way to accomplish this is by finding valuable uses for waste products. This particular project will redirect the waste product of a local coffee business, coffee chaff, to serve as a material for a local community garden. Coffee chaff is often burned, releasing more carbon, but has potential as a beneficial input for agriculture. This project will aim to study the benefits of utilizing this waste as mulch, which include moisture retention, increased nutrient availability, and improved yield. Little has been reported on the effectiveness of coffee chaff as mulch, so this project will address this gap. Also, our project will evaluate the potential for a sustainable, local source of garden nutrients to further support local food production. Specifically, our project will be in collaboration with Tiny Footprint Coffee who will be providing the coffee chaff.


Our research questions are: How can common waste products be used to increase local food production? Is coffee chaff (i.e., the husk from a coffee fruit) an effective mulch for urban agriculture?


This study is taking place at the urban garden at West 7th community center in St. Paul, which was established by the University of St. Thomas in 2014 and is leased from the St. Paul Parks and Recreation department. This urban garden has thirty-two 2×2 meter plots. We will use a factorial design: plots will receive coffee chaff only, wood chips only, chaff and wood chips, or no mulch. For the appropriate treatments, the same volume of coffee chaff and/or mulch will be applied on top of the soil or mixed in the top 4 inches of soil at the beginning of the summer. The same number and types of tomatoes, peppers, eggplants, and potatoes will be grown in all the plots; these plants represent a mix of root and fruit crops, and are all susceptible to common diseases. As a result, they should allow for a general assessment of the value of our mulches.


Soil moisture will be measured multiple times during the summer by using digital soil moisture meters. Soil samples will be sent to the University of Minnesota lab to measure soil nutrients (e.g. phosphate, nitrate, potassium, organic matter, pH) three times during the project period. Yield will be measured by weighing all harvested crops throughout the summer. Evidence of pests will be measured by counting the evidence of tomato leaf spot. Eco-plates will be used to analyze the soil microbes. Amount of weeds will also be weighed throughout the project period. The main statistical analysis will be a two-way Multivariate Analyses of Variance (MANOVA) to compare outcomes associated with the different treatments.


We predict that coffee chaff will be comparable to wood chips, a standard ground cover, for its effectiveness for retaining soil moisture, soil nutrient levels, yield, soil microbes, and the amount of weeds.  We predict that the chemicals in coffee chaff will have antimicrobial properties and therefore, be more effective than wood chips at controlling tomato leaf spot virus.