Effect of caffeine on plant growth
The mung beans watered using the coffee mixture will grow the fastest.
Caffeine and plant growth
The effect of adding caffeine to the soil and its effect on plant growth is a subject that has been studied for quite some time. Some plants seem to benefit and grow faster when caffeine is added to the soil, while others seem to become stunted or grow slower. There are also some plants that are not affected by the presence of caffeine in the soil.
Caffeine can be introduced to the soil by sprinkling grounded coffee over the soil, adding leftover coffee to the pot or watering with a caffeine solution made by dissolving a caffeine tablet in water. The grounded coffee is actually organic matter and will help in adding nutrients to the soil. It will also attract worms that feed on the grounded coffee and at the same time help to aerate the soil.
Many gardens are known to add grounded coffee to the soil in order to accelerate plant growth. However, it is not clear whether the improved growth is due to the caffeine or the presence of potassium and phosphorous in coffee. It is also possible that caffeine retards plant growth but the presence of potassium and phosphorous in coffee reverses this effect.