1. The Effect of Black Walnut on the Germination of Tomato Seeds
Jamie Poduslenko

2. Question
Do solutions made with the leaves and hulls of black walnut trees have an effect on tomato seeds’ ability to germinate over a time period of four weeks?

3. Background Information
The nuts of a black walnut tree are enclosed by a brown flesh, called the hull.
Black walnut trees are one of the most commonly known allelopathic plants.
Allelopathic plants have the ability to inhibit plants’ growth because they release chemicals that are highly toxic to the other plants. All parts of a black walnut tree contain juglone, a toxic chemical to some species of plants.
Juglone deprives sensitive plant species of needed energy to live. It is produced and most concentrated in the roots of the black walnut tree.

4. Hypothesis
When tomato seeds germinate in the presence of a black walnut leaf or hull solution, their root lengths will be significantly shorter than tomato seeds germinated in the presence of distilled water.

5. Materials
4 nuts from a black walnut tree and a branch with leaves from a black walnut tree
Distilled Water
Tomato Seeds
Household Bleach
24 Petri Dishes and pieces of filter paper
Sealable Plastic Bags
Journal to record results

6. Procedure
Four nuts from a black walnut tree and a branch with leaves were collected from a live black walnut tree.
Thirty grams of the hull surrounding the nuts was sliced off and added to an 800 mL beaker of boiling water to create a solution with a concentration of 3.75%.
30g of the leaves were crushed and added to a separate beaker that contained 800 mL of boiling water.
The beakers soaked overnight and the pieces of leaves and hull were drained from the solutions the next morning.
The two solutions were diluted three times, by a factor of 10 each time (a total of 6 solutions: black walnut hull solution 1: 3.75% concentration, solution 2: 0.375%, and solution 3: %, and black walnut leaf solution 1: 3.75%, solution 2: 0.375%, and solution 3: %).

7. Procedure Continued The tomato seeds were bleached.
Poured into a beaker that contained 90 mL of distilled water and 10 mL of household bleach.
The seeds were left to soak for 20 minutes, drained, and left out to dry.
Five mL of black walnut hull solution was added to each of the first 3 dishes, along with 5 bleached seeds in each dish.
The process of adding 5 mL of solution and 5 seeds to a dish was repeated until all of the hull solutions created had been used to saturate the seeds in 3 dishes.
Five mL of black walnut leaf solution was added to 3 dishes, along with 5 seeds in each dish
The process of adding 5 mL of solution and 5 seeds to a dish was repeated until all of the fruit solutions created had been used to saturate the seeds in 3 dishes.
The same process was used to create the control group, except 5 mL of distilled water was used to saturate the seeds in 3 dishes.
All of the dishes were sealed in plastic bags and left to germinate for 4 weeks.
After 4 weeks, the bags were reopened and each seed’s root length was measured in millimeters and recorded in a journal.

8. Variables and Constants
The location of the dishes throughout the germination process
Amount of solution used in each dish
Number of seeds
Amount of time given to germinate
Amount of light seeds were given
Type of dish and filter paper used
Black walnut leaves and hull were all from the same tree
Independent:
The concentration of black walnut solution used
Dependent:
The root length of the tomato seeds after being saturated in black walnut solution for 4 weeks.
Add the control to your slide

9. Data: Germination Rate

10. Data: Germination Rate

11. T-Tests
Ctrl+ Leaf Soln. 3
0.483
Ctrl+ Leaf Soln. 2
0.269
Ctrl+ Leaf Soln. 1
0.151
Ctrl+ Hull Soln. 3
0.980
Ctrl+ Hull Soln. 2
0.767
Ctrl+ Fruit Soln. 1
0.230
T-Tests were performed and revealed that the data collected is not statistically different enough to consider that seeds were affected by the black walnut solutions. The two variables compared in each t-test was each concentration of solutions’ average root lengths vs. the control group.

12. Conclusion
There is a general pattern of decreasing root lengths of seeds as the solution becomes more concentrated, but no significant effect of black walnut fruit and leaf solutions on the tomato seed’s germination.
The allelopathic effects of black walnut trees did not impact the tomato seeds’ germination in this experiment
Sensitive plants should not be grown in close proximity to the black walnut tree, but they have a chance of being unaffected by the black walnut if only a small amount of juglone is present.
The original hypothesis was rejected.
Spelling of original

13. Limitations Further Studies
Several seeds from each test did not start to germinate, so their root lengths were recorded as 0
Possibly the result of seeds that were defective or seeds that contained no embryo, also known as “empty seeds”
Only one type of seed was tested
Results may be different for different types of seeds.
Further Studies
Higher concentrations of juglone used in solutions
Different types of seeds tested to see if the solutions would affect them differently than they affected the tomato seeds.
Test other known allelopaths to see which has the greatest impact on seeds’ germination.

14. References
Appleton, B., Berrier, R., & Harris, R. (n.d.). The Walnut Tree: Allelopathic Effects. Virginia Cooperative Extension. Retrieved from
Bir, R. E. (2009, February 12). Black Walnut (Juglans nigra) and Allelopathy. Retrieved October 3, 2011, from North Carolina State University Cooperative Extension website:
Black Walnut Toxicity. (n.d.). West Virginia University Extension Service. Retrieved from
Brooks, M. (n.d.). Effect of Black Walnut Trees and their Products on other Vegetation (Vol. 347). (Original work published 1900) Retrieved from
How to Germinate Seeds to Get Best Results When Growing Tomatoes from Seeds. (2011). Retrieved October 16, 2011, from
Juglone in Black Walnut Trees. (2011). Retrieved October 4, 2011, from
Kennell, H. S. (1999, September). Seed Germination. Washington State University Extension. Retrieved from
Ombrello, T. (n.d.). BLACK WALNUT. Retrieved October 15, 2011, from ombrello/‌pow/‌Plant-List.htm
Ostermiller, S. (1997, July). Juglans Nigra. In Black Walnut. Retrieved October 15, 2011, from
Parts of the Seed. (2006). Retrieved January 17, 2012, from