Effects of Coffee Grounds on the Growth of Tomato Plants

¶ … stimuli can affect plant growth rates, robustness, flowering, and even fruit production. We also know that nitrogen is an important part of plant development, and contributes significantly to the thickness, leaf count, and stem width in most plants. A plant that is nitrogen deficient is generally small and develops slowly because it lacks the nitrogen necessary to manufacture adequate structure and genetic materials. This could leave the structure pale green, because it lacks adequate chlorophyll. On the other hand some plants may grow rapidly when supplied with excessive nitrogen. They develop protoplasm faster than they can build sufficient supporting materials in cell walls. The plant may grow weaker and be prone to more pathogens or injuries while developing smaller fruits or fruits with less seeds (Foyer and Zhang, eds. 2010).

Background- Coffee grounds have long been known to increase compost value and act as a fertilizer in plants. In fact, over 10% of coffee grounds are nitrogen-rich proteins that are typically expressed in an 11:1 ratio, ideal for plants. In addition, there are base oils, lips, and fatty acids that remain in the grounds and are slowly decomposed within the soil, and make bioavailable to the plant roots (Chalker-Scott, 2009).

Research Questions-

1) At what concentration will the nitrates from the coffee grounds produce a healthier plant? Looking at heights, increase amounts of leaves, flowers, and fruit.

2) What are the nitrates producing or changing in the soil to help cellular production?

Methodology - Using "Grow Lights" of appropriate solar spectrum, peat pots, commercial potting soil, coffee grounds and tomato seeds, five different planting media: 2 control 100% commercial potting soil and 2 100% coffee grounds; along with 6 pots of 3 different ratios of mixed soil and coffee grounds were studied. Height measurements were taken every 10 days for 7 weeks; the total experimental time was 40 days. Aged water and a mixture of 50/50 water and brewed coffee were used to hydrate the plants based on the following table:

A- Water with aged water:

100% soil

1:4 soil/coffee grounds

1:1 soil/coffee grounds

3:4 soil/coffee grounds duplicate

Duplicate

Duplicate

duplicate

B - Watered with 50/50 brewed coffee and water:

100% coffee grounds

1:4 soil/coffee grounds

1:1 sol/coffee grounds

3:4 soil/coffee grounds

Duplicate

Duplicate

Duplicate

Duplicate

Hypothesis- More growth should be apparent within the first few weeks of planting tomato seeds in a moderate soil/coffee ground mixture. Using a 50/50 ratio of water and brewed coffee as a hydration mechanism should also increase growth rate.

Results - (See Appendix A). Group A, the group with soil and aged water as hydration, showed more growth for the control in this case, than in the other variables. In fact, the next closest variable, a top layer of coffee grounds, was still, on average, 35% below the control, even by conclusion of the experiment. In Group B, the differences between the variables were less robust, but even the top performer did not match the control variable in Group A. In fact, our results show a decided decrease in robustness and health of the plants with larger amounts of coffee grounds (A) or coffee grounds with coffee water (B). Using a 50% soil solution result in only 4cm for both A and B. At the conclusion of the experiment.