Improving Resilience, Sustainability and Nutritional Properties of Specialty Crops Using Composted Spent Coffee Grounds

Progress report for GS19-209

Project Type: Graduate Student
Funds awarded in 2019: $16,044.00
Projected End Date: 08/31/2022
Grant Recipient: Texas A&M University
Region: Southern
State: Texas
Graduate Student:
Major Professor:
Dr. David Reed
Texas A&M University
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Project Information


To improve competitiveness of producers while addressing the lack of consistent fruit and vegetable consumption among Texans, Texas A&M AgriLife Research will investigate the effectiveness of composted spent coffee grounds in increasing nutritional properties (nutrients, vitamins, antioxidants) of spinach, pepper, basil, nasturtium, and oyster and shiitake mushrooms. The effect of composted spent coffee grounds on growth and yield of these specialty crops will also be assessed. The spent coffee grounds will be provide by a cold brew company in San Antonio.

Outcomes of the proposed research include:

  • Enhance sustainability and profitability by providing a cost-effective, locally sourced soil amendment for nursery and vegetable crops, and mushroom substrate for growers.
  • Decrease the amount of spent coffee grounds going into landfills by developing research-based data to support composted spent coffee grounds as an agricultural and horticultural commodity.
  • Provide consumers access to vegetables/mushrooms with higher-than-average nutritional benefits.
  • Increase marketability and expand consumption of fruits, vegetables and mushrooms.
Project Objectives:
  • Develop research-based data to establish composted spent coffee grounds as a viable soil amendment/substrate and peat substitute for mushrooms, spinach, pepper, basil, and nasturtium, creating more sustainable and cost-effective practices.
  • Improve competitiveness of mushrooms, spinach, pepper, basil and nasturtium by enhancing their nutritional properties, yields, and marketability without increasing economic inputs.
  • Partner with the relevant stakeholders to implement the use of composted spent coffee grounds in sustainable agricultural production systems.


Click linked name(s) to expand
  • Dr. Benjamin Wherley (Educator and Researcher)
  • Dr. Julie Howe (Educator and Researcher)
  • Dr. Elizabeth Pierson (Educator and Researcher)
  • Dr. Sherry Tanumihardjo (Educator and Researcher)
  • Mikayla Kaeppler (Researcher)


Materials and methods:

Non-composted, static pile composted and/or in-vessel composted spent coffee grounds were tested for phytotoxicity using germination and growth experiments. Germination and growth experiments were carried out at the Texas A&M Department of Horticultural Sciences, Horticulture Teaching Research and Education (Hort. T.R.E.C.) greenhouse facility. The spent coffee grounds used throughout this study came from a cold brew coffee company based in San Antonio, TX. Pro-Mix general purpose potting mix was the peat-based media used in these experiments. Potting mixture treatments were made on a volume/volume basis and mixed by hand. Treatments included 10%, 25%, 50%, 75% and 90% SCG and potting mix in order to cover the full spectrum of the effect on the plant at high and low levels of SCG. The first eggplant experiment also included SCG and sand at the same ratios as above. These treatments were not repeated due to the difficulty and poor results of using sand in nursery pots.

Germination experiments

Each mixture was spread evenly into seedling trays (25 cm wide by 51 cm long, and 6.4 cm deep) with forty seeds per tray. Each tray was replicated three times. Seeds tested included Pisum sativum ‘Wando’ bush peas, Spinacia oleracea hybrid #7 spinach, and Raphanus sativus, Cherry Belle radish. Percent germination was calculated.

Growth and phytochemicals

Solanum melongena ‘Patio Baby’ were planted into seed plug trays (2 cm by 4 cm cell size), one seed per plug, filled with seedling potting mix (Pro-Mix general purpose seedling mix). Eggplants were transplanted into 20 cm nursery pots after the first set of true leaves were fully developed. Each treatment had five replicates given a high fertilizer rate (15-5-25 at 0.4 g/L) and five replicates given a low fertilizer rate (15-5-25 at 0.1 g/L). Plants were watered daily using a dosatron set at a dilution rate of 1:100 The sand and potting mix treatments were sperate experiments, assigned to different benches with pots arranged in a Completely Randomized Design. Data collected on a weekly basis included: height, number of flowers and fruits. Nine weeks after transplanting the eggplants were harvested and fresh weight was recorded as well as fruit number, fruit weight, and fruit length. Eggplants were left on greenhouse benches to dry until a constant weight was achieved, and dry weight was recorded. This experiment was repeated but did not include the sand treatments because the sand did very bad in the pots. It also only included a high fertilizer rate because there were no differences between the high and low fertilizer treatments. 

Ocimum basilicum ‘Rutgers obsession’ seeds were started in 3.8 cm rockwool cubes and transplanted according to the methods described above. Treatments included potting mix and static-pile composted SCG, and potting mix and non-composted SCG with ratios the same as previously stated. A high fertilizer rate (15-5-25 at 0.4 g/L) was applied to all treatments, with five replicates per treatment and in a completely randomized design. Data collected on a weekly basis included: height, number of flowers and branches. Eight weeks after transplanting the basil was harvested and fresh weight was recorded. Basil plants were left on greenhouse benches to dry until a constant weight was achieved, and dry weight was recorded. 

After the plants were harvested eggplant fruits and basil leaves were placed in zip-loc baggies and stored in a deep freezer. Samples were freeze dried and mailed to UW Madison Department of Nutritional Science for analyses. Chemical analysis of eggplant fruit and basil leaves using HPLC and LC-MS were used to identify carotenoids (carotenes [beta-carotene, alpha-carotene], xanthophylls [lutein]). Methods for the flavonoids (anthocyanins: nasunin, pelargonidin, cyanidin, peonidin, malvidin, petunidin and delphinidin) analysis are being reviewed.  Data will be compared to published nutritional value data for the same crops. A total of 80 samples were analyzed, 25 basil leaf samples and 55 eggplant fruits. Basil samples will be from 0%, 10%, and 25% non-composted and static-pile composted SCG treatments with five replicates from each treatment. Eggplant fruit samples will consist of 0%, 10%, 25%, 50%, 75% and 90% non-composted and static-pile composted SCG treatments with five replicates from each treatment. 

Mineralization Rate of SCG

A 73-day incubation experiment was conducted to determine the nitrogen and carbon dioxide release dynamics of SCG. the objective of this incubation study is to characterize nitrogen mineralization dynamics of composted and non-composted SCG in relation to other commonly used nitrogen fertilizers. Based on the first incubation of 73 days as well as growth experiments that showed an increased growth rate after about 42 days, we expect the inorganic nitrogen in the composted SCG to be available to the plant sooner than the non-composted SCG. This laboratory incubation study was conducted at Texas A&M University during Fall 2019. Non-composted SCG, composted SCG, Milorganite (5-2-0), and Urea (46-0-0) fertilizers were mixed into 50 g of Booneville fine sandy loam soil at 9.8 g N m-2. Microcosms were held at 25 °C for 73 days and sampled every 7 days to measure CO2 release. Ammonium (NH4+), and nitrate (NO3) extraction method followed Keeney and Nelson (1982). Experimental layout was in a Completely Randomized Design.

In July 2021 another incubation experiment lasting 90 days will determine the effect of time on the mineralization of in-vessel composted and non-composted SCG compared to other commonly used nitrogen fertilizers. Non-composted SCG (2.2-0.9-0.5), in-vessel composted SCG (3.5-0.1-0.7), Milorganite (5-2-0), and Urea (46-0-0) will be mixed with a fine-sandy loam soil for comparison. The soil will be brought to filed capacity (60% w/w) and a 9.8 g N m-2 rate of each treatment will be added to 50 g dry-weight soil. Treatments will be thoroughly mixed in 50 ml polypropylene beakers. Each beaker will be placed inside a Mason jar with 5 ml of water in the bottom to create a microcosm. A CO2 trap which consists of a 50 ml polypropylene centrifuge tube, with no lid, filled with 20 ml of 1.0 M sodium hydroxide will also be placed in each Mason jar. The jars will immediately be sealed and placed in an incubator held at 25 °C. Aerobic conditions will be maintained by opening the jars every 7 days. The sodium hydroxide trap will be sampled weekly by adding barium chloride and back titrating with hydrochloric acid (HCl) to measure CO2 release. The amount of HCl used in the titration will be recorded and used to create a cumulative CO2 graph. We will measure CO2 flux as an index for net mineralizable nitrogen. Ammonium (NH4+), and nitrate (NO3) extraction method will use inductively coupled plasma spectrometry (ICP), and destructive samples will be measured throughout the 90-day incubation. We will also measure CO2 flux as an index for net mineralizable nitrogen. 


Research results and discussion:

One-way ANOVA followed by a Tukey’s HSD post hoc test for multiple comparisons among means was used to detect differences in germination, growth, and phytochemical concentrations among the different treatments.


Peas: There were no significant differences among treatments at day 21. Day four emergence was significantly greater in 50:50 treatment than higher rates of CSCG.
Spinach: Germination percentage was significantly lower in control at day 21 compared to all other treatments. Day six emergence was significantly greater in 75% CSCG compared to all other treatments. Addition of CSCG results in possible increased germination for peas and spinach. Radish: data from the second set of experiments are being analyzed to verify results.

Addition of static-pile composted SCG resulted in decreased time to germination for peas and spinach. At a rate of 75 % static-pile composted SCG with media (sand and potting mix) showed the highest germination rate for spinach. The first four days of germination were the highest for peas in all treatments, and for spinach in 75% SCG. The germination experiments in 2019 and 2020 showed similar results. Chrysargyris et al. 2019 tested germination of brassica seeds in mixtures of peat and SCG of 2.5, 5, and 10%. They found cabbage germination was stimulated at 2.5% SCG and cauliflower at up to 5%. At 10% SCG the percent germination decreased but mean emergence time increased. They concluded that up to 5% SCG could be used as a bio-stimulant and or partial peat replacement for brassica seedlings. These results are similar to what were found in our experiments although the percent of SCG used was much higher. This could be due to the fact that our SCG were composted and the plant species tested. It would be interesting to test brassica species in composted SCG.  Release of toxic substances particularly from non-composted SCG have been attributed to inhibited germination and growth in some plants (seed germination alfalfa (Medicago sativa), clovers (Trifolium repens and T. pretense); growth Chinese mustard (Brassica juncea), komatsuna (Brassica campestris), Italian ryegrass (Lolium multiflorum), inch plant (Tradescantia albiflora), geranium, and asparagus fern.


Eggplant: Fresh weight is significantly higher in composted than non-composted SCG across all treatments. Non-CSCG reduced growth and stunted development in all treatments compared to composted SCG.
Basil: Plants died in treatments >25% non-composted SCG. There were no significant differences in fresh weights in treatments <50% composted and non-composted SCG. Differences between composted and non-composted SCG could be due to phytotoxicity, which is removed after composting. Calcium deficiency could cause tip death.

After day 41 at a high fertilizer rate differences in eggplant height between potting mix and static-pile composted SCG treatments and control diminish, possibly due to inorganic N mineralization of the static-pile composted SCG. At a low fertilizer rate, height compared to high fertilizer treatment is comparable, possibly due to addition of the static-pile composted SCG. In sand at high fertilizer rate, after day 45 treatments with higher ratios of static-pile composted SCG have greater average height. Possibly due to a combination of inorganic N mineralization, lower bulk density and increased pore space. In sand at a low fertilizer rate, after day 41 static-pile composted SCG contribute inorganic N and improve soil physical properties, shown in greater average height of treatments over control.


Carotenoid analysis is complete and being reviewed. Anthocyanin methods are being revised. The carotenoid and anthocyanin levels of eggplants and basil are expected to be positively correlated up to as much as 50 percent of static-pile composted SCG and 5% for non-composted SCG. Phytochemical concentrations are known to differ between varieties which could be a factor in comparing the ‘patio baby’ to published data on carotenoid and anthocyanin content of other eggplant varieties. In cabbage and cauliflower phytochemicals increased in up to 5% SCG but decreased with higher amounts of SCG, although broccoli showed no difference from the control in any treatments (Chrysargyris et al., 2019b). The SCG used in our experiments were composted and were able to be used at higher percentages in eggplant without decreased growth.

Mineralization Rate of SCG

Despite their relatively favorable N content (2.3%N) and C:N ratio (20:1), SCG appear slow to mineralize. Net immobilization of N was seen during the initial 42 days, with net mineralization of N occurring later on. No significant differences were seen between fresh and composted SCG for any of the parameters tested. The high levels of CO2respiration observed with SCG demonstrates higher amounts of microbial activity are required for the breakdown of SCG, relative to other fertilizers. Given that N mineralization appears slow, the positive benefits previously seen following sand amendment suggest microbial or physical factors may be responsible.

Participation Summary

Educational & Outreach Activities

2 Curricula, factsheets or educational tools
6 Webinars / talks / presentations
14 Mentored undergraduate students participating in the Aggie Research Program. Students applied to participate in our research project to gain experience. In the Fall of 2020 I mentored six students and in the Spring of 2021 I mentored seven students. The students assisted with maintaining experiments and data collection. Two students participated in Student Research Week and presented a poster on the research they helped with.
Presented initial research to Colin County Master Gardeners Association.

Participation Summary:

4 Ag professionals participated
Education/outreach description:

Presentations and Published Abstracts

In 2020, four presentations on our spent coffee grounds research were given. Initial research was presented to the Collin County Master Gardeners Association CollinCo.SCGpres.2020ALB. Collaboration with a post-doc and PhD student at the Energy Institute at Texas A&M resulted in two presentations: 1. Circular economy systems engineering for food supply chains: A case study on the coffee supply chain. International Conference on Sustainable Development ICSD 2020_CE Systems Engineering_Styliana; 2. Circular economy systems engineering: A case study on the coffee supply chain. American Institute of Chemical Engineering Abstract_Chemical Engineering_Stefanos_Styliana2020A poster on the mineralization rate and CO2 release of spent coffee grounds, and their potential use as a slow-release fertilizer was presented at the Agronomy Society of America International Annual Meeting Amanda-Incubation Experiment_ASA poster2020Final

In 2021, a poster was presented at Student Research Week, at Texas A&M. This included undergraduate students, who applied through the Aggie Research Program, to assist with certain aspects of our spent coffee grounds project in order to gain research experience. The title of this poster was “The Effect of Spent Coffee Grounds on Germination and Growth of Container Grown Specialty Crops.”Germination in media_SRWposterSpring 2021

In August, 2021, a poster will be presented at the American Society of Horticultural Sciences annual meeting in Denver titled “Spent Coffee Grounds Have a Biostimulant Effect on Germination of Spinach, Peas, and Radish.”

In November, 2021, a poster will be presented at the Agronomy Society of America annual meeting in Utah. This poster will update the use of spent coffee grounds as a slow release fertilizer. It will be based on an ongoing experiment that will verify results of a previous experiment and provide additional data by extending the time span of the experiment from 60 days to 90 days. 


Mentored undergraduate students participating in the Aggie Research Program. Students applied to participate in our research project to gain research experience. In the Fall of 2020 I mentored six students, and in the Spring of 2021, I mentored seven students. The students assisted with maintaining experiments and data collection. Two students participated in Student Research Week and presented a poster on the research they helped with.

Gave a presentation to the Colin County Master Gardeners Association and had lunch with them. A number of people were very interested in my research and we exchanged emails. They expressed interest in seeing my final results.

Project Outcomes

2 New working collaborations
Project outcomes:

Through our research experiences we have found promising applications for spent coffee grounds such as a biostimulant for seed germination, a substitute for peat based potting mix, a slow release fertilizer, and increased levels of some carotenoids. We have also learned that some plant species have a positive response, and some have a negative response to the application of spent coffee grounds. Additionally, we saw that spent coffee grounds are highly compostable using different methods and can be used as the primary, or even only, feed stock for composting. All of this knowledge will contribute to sustainability by providing a use for a waste product, spent coffee grounds, and creating a circular economy. By using them as a substitute for peat moss, germination media, additive to increase certain carotenoids, compost feedstock, and slow release fertilizer, large quantities will be taken out of the waste stream and replace other materials that would have to be harvested from the environment. 

Knowledge Gained:

During the course of this project we have learned that there is increasing interest in sustainable agriculture by people from many different backgrounds. Farmers, gardeners, educators and those interested in circular economy have all shown interest and support for researching the use of spent coffee grounds in agriculture and horticulture. We have become more aware of the potential for many different groups adopting the use of  spent coffee grounds in a variety of real world applications. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.