The Germination of Lettuce Seeds


Will the presence of the substance garlic affect the germination of lettuce seeds? In this experiment I will be observing the effects a process known as Allelopathy and the role it plays on lettuce seed germination. The volatile of garlic will be experimented in order to observe what type of affect it will have on the germination of lettuce seeds.


Allelopathy is "any direct or indirect harmful or beneficial effect of one plant... on another through production of chemical compounds that escape into the environment" (Rice, 1984). These chemicals once released can inhibit or stimulate the growth of plants. To be more specific it is called Volatiles; chemical compounds that vaporize or evaporate quickly. Crushed garlic produces a bioactive volatile called Allicin. Studies have shown that allicin has the ability to prevent the growth of micro-organisms and the germination of seeds. This phenomenon happens as a result of the allicin protecting the damaged garlic from micro-organisms and competition from other plants for sustenance. In my hypothesis I concluded that the lettuce seeds once exposed to the garlic will have a negative effect on its growth and development.


  1. 4 Petri dishes with covers
  2. 8 pieces of filter paper
  3. 100 lettuce seeds
  4. 2 grams of carrots
  5. 2 grams of garlic
  6. 25 ml distilled water
  7. Triple Beam Balance
  8. Blade
  9. Masking tape
  10. Pipette
  11. Garlic press
  12. Red marker
  13. Tin foil boat


In this experiment four petri dishes were used to conduct the growth of the lettuce seeds. In each petri dish contained 2 pieces of filter paper, 25 lettuce seeds and 5 ml of water. There were three experimental groups and one control group. The experimental groups would receive either garlic or carrots inside the petri dish, while the control group received neither. Specifically, 1 gram of chopped carrots was added to one petri dish along with the seeds. Another petri dish contained one gram of garlic alongside the seeds, while the third dish containing both one gram of carrots and garlic a piece. Finally, the control group would be the one whose petri dish contained the 25 lettuce seeds alone.

The petri dishes were contained, sealed off, and observed for three weeks. The growth of the lettuce seeds was recorded once a week for three week; with the independent variables being the carrots and garlic. The dependent variable being what is measured; this is the sprouting of the seeds, and the plant growth relative to one another. All of the dishes were exposed to the same environment, with the same temperature, sunlight in order to eliminate any unexpected variables.

RESULTS (Collected Data)

The result of this experiment determined garlic alone has a negative effect on the growth of lettuce seeds. Throughout the time span of three weeks I observed that the seeds without exposure to garlic grew more than the seeds with exposure to garlic. During the first week of observation, all of the groups germinated and grew at a similar rate. Each had an average of 5 or 6 seeds germinate and grew an average of 0.4 of an inch from root to stem. Differences amongst groups began to show by the second week of observation. The seeds with carrots at three inches and the lettuce seeds without exposure to garlic (control group) at three inches were growing slightly larger than the lettuce seeds of the other experimental groups. The lettuce seeds with exposure to garlic grew one inch, while the seeds exposed to both carrots and garlic grew two inches. Both of these two experimental groups slowly fell behind when in comparison to the control group as time passed.

In the final week, the control group with the lettuce seeds not exposed to garlic/carrots grew to 3.5 centimeters long with 3 sprouting leaves. The lettuce seeds with exposure to garlic had fewerlettuce seeds germinate. The lettuce seeds grew only to 1 centimeter long from root to stem and the majority died by the third week. The seeds with the carrots grew partially shorter at three centimeters with two sprouting leaves. This demonstrated that garlic indeed has a negative effect on the growth of lettuce seeds. The lettuce seeds exposed to both garlic and carrots grew 3.5 centimeter and had 3 leaves. As a result, it is not proven that garlic will prevent the growth of other lettuce seeds; however, it is heavily implied.


In my hypothesis my earlier prediction proved to be correct; but, my results contradicted with one another in the end. The petri dish that contained both lettuce seeds with exposure to carrots and garlic did not seem to have the same negative effect on the growth of lettuce seeds; they grew as fast and as healthy as the control group with no exposure to garlic. My experiment found the same results. The lettuce seeds with exposure to garlic grew in less numbers, died faster, and grew shorter when compared to the other groups. Essentially, this experiment agreed with my hypothesis that exposure to garlic will have a negative effect on the germination and growth of lettuce seeds.


  • Beeber,Carla. Bierman, Carol. Hinkley, Craig. Lakrim, Mohamed. Lanzetta, Peter. Lind, Georgia. Markus, Theodore. Ortiz, Mary. Pilchman, Peter. Polizzotto, Kristin. And Stavroulakis, Anthea. General Biology I: Laboratory Manual. Fifth Edition Retrieved on 1/29/10.
  • Davies, Gareth. "" 22 March 2008. Garden Organic. ⟨⟩. Retrieved on 1/29/10.
  • Salazar, Ronald M. 1998. ⟨⟩. Retrieved on 1/29/10.
  • Rivensheild, Andrea.2002. "Allelopathy" ⟨⟩ Retrieved on 2/8/10

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