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How will fertilizer affect the growth of tomato plants?

How will fertilizer affect the growth of tomato plants?

Sydney Palmer – 5th Grade Science Project at Mariner’s Elementary School in Newport Beach, CA


I was able to do my science fair project because I had access to all the right materials, and I was very interested in learning about, and taking care of tomato plants.  I chose to investigate how the growth of tomato plants would be affected by the addition of fertilizer because it seemed like a very interesting topic to research.  Tomato plants were also a good choice for me because they are simple to grow, and grow relatively quickly.  Quick growing plants were necessary because I only had a short time span, approximately one month, to conduct my experiment.  Because tomato plants grow relatively quickly, I will be able to see noticeable growth within the one-month time period.


I predict that the tomato plants with fertilizer will grow to be taller and healthier than the plants grown without fertilizer.  I also predict that the tomato plants grown with fertilizer will have a better developed root system than those grown without fertilizer.

Materials List

1.     6 of the same size tomato plants (Roma)

2.     6 large pots

3.     Water

4.     Soil with no added nutrients (Dutch Blend)

5.     Watering can

6.     Ruler or measuring tape

7.     Fertilizer (Green’s Green)

8.     Camera

9.     Measuring cup


1.     Buy 6 tomato plants, fertilizer, 6 large pots, and soil without added nutrients (Dutch Blend)

2.     Plant the tomatoes in the pots with equal amounts of un-amended soil.

3.     Get 6 stickers.  Label the 3 pots with fertilizer F1, F2, and F3 and label the 3 plants without fertilizer N1, N2, and N3

4.     Water the plants with enough water to completely saturate the soil.

5.     Measure the plants height once a week and keep track of the measurements on a chart.

6.     Fertilize 3 of the plants with Green’s Green once per week.

7.     Mix 1 teaspoon of fertilizer with 1 gallon of water and give each of the 3 fertilized tomato plants 32 ounces of the fertilized water.  Then give the remaining 3 tomato plants 32 ounces of plain water.

8.     Water all of the plants with 52 ounces of water every 3 days.

9.     At the end of one month, figure out the average rate of growth for the 3 tomato plants with fertilizer, and the average rate of growth for the 3 tomato plants without fertilizer.

10.  Compare the results.


At the beginning of my experiment I observed all of my plants.  I noticed that they were all about the same size, and they all appeared to be healthy.  I planted them on a sunny day in exactly the same conditions.  They were planted in pots and kept in the courtyard of my house.

I noticed that after about 10 days, I started to see a difference in growth and height between the six tomato plants.  I also started to see a difference in the amount of leaves each tomato plant had.  All the fertilized plants grew taller and had more leaves because these plants had nutrients.  The un-fertilized plants which had no nutrients to help them grow were shorter and had fewer leaves.

May 3, 2011, 8:00 A.M. Courtyard

I began to notice a big difference between the fertilized and the un-fertilized tomato plants.  I noticed that F3 was by far the tallest plant, and had the largest leaves.  I noticed that N1 was the smallest and least healthy of the tomato plants.  I could also tell the difference between the six pots of tomato plants.    I noticed that the three un-fertilized plants had much yellower leaves than the three other tomato plants.

May 10, 2011, 8:00 A.M. Courtyard

I noticed that F1 had a much fatter trunk than the others had.  I noticed that some of the leaves on the un-fertilized plants had spots on them.  The fertilized tomato plants had much bigger leaves, and there were many more leaves coming from their trunks.  The un-fertilized tomato plants had smaller leaves and skinnier trunks than the fertilized plants did.  F3 of the fertilized plants had especially huge and healthy leaves.  Some other things that I noticed were that N1 had two trunks, N2 was leaning to the right side, and that N1 looked much smaller and unhealthy than the other tomato plants.

May 22, 2011, 8:00 A.M. Courtyard

I began to notice that N1 seemed to be dying because it wasn’t getting the nutrients it needed to grow.  N2 and N3 were surviving, but were turning a little bit brown and the leaves were drooping.  The F tomato plants were healthy, tall, had flowers, had lots of nutrients, and they were very pretty.


From my research and findings of not just tomato plants, but all kinds of plants, I found out lots of information about fertilizer.  One example is that fertilizer has a lot of nutrients in it.  Fertilizer can make a big difference in plants’ growth.  You can tell by just looking at two of the same types of plants, one with and one without fertilizer.  The one with fertilizer will look a lot healthier because of all the nutrients that it has, and the one without fertilizer won’t look as healthy.  I can tell that tomato plants aren’t healthy if the plants have brown or yellow leaves, fewer branches, drooping leaves and branches, fewer leaves, darker vein.  Basically the plants without fertilizer or nutrients look like they are starting to die.  On the other hand, a healthy plant has a bright green color, many leaves and branches, and will grow taller and wider.  So, now every time I grow any type of plant, I will always use fertilizer.


My family has been a big help to me this entire project.  My dad has helped me with all the planting, watering, fertilizing, and photographs.  My mom has also helped me with the fertilizing, watering, and measuring.  My little sister helped me come up with good ideas for the topic of my science fair project.  My family has been an outstanding help to me!

I would also like to thank Salam Awada, PhD for helping me choose my fertilizer.

Future Research

In the future, I would really like to keep working on this project.  I really want to keep doing this with my family so that we can have lots of tomatoes this summer.  I am interested to see how many tomatoes we are able to harvest from the fertilized plants versus how many we will be able to harvest from the un-fertilized plants.

I would also sometime like to try this project again, but with different types of fruits and vegetables, besides tomatoes.  I would also like to use different amounts of water and fertilizer in my future experiments to see what would happen.


I thought that the three tomato plants with fertilizer would grow the tallest and be the biggest.  I found that fertilizer makes a big difference in plants.  My data showed that by the last measurement the average height for the tomato plants with fertilizer was 39.3 centimeters.  The average height for the tomato plants without fertilizer was 27.6 centimeters.  I got my results because I was consistent with caring for, and measuring my plants.

Although water and fertilizer helped my plants to grow, I had to be careful to give them just the right amount. From my research I learned that adding to much water or fertilizer to the tomato plants could have affected my results in a negative way because they would have been overwatered, or even burned from too much fertilizer.

In the future I would like to continue to investigate the growth of my tomato plants.  I am interested to see how many tomatoes the fertilized plants produce, versus how many the un-fertilized plants produce.



Maruyana, Susan J. Sunset Western Garden Book.  Menlo Park, California: Sunset Publishing Corporation.  1995.


“Tomatoes-Lycopersicon Esculentum”, All-New Encyclopedia of Organic Gardening. Emmaus, Pennsylvania:  Rodale Press, 1992 .  p.p. 569-573.


http://en.Wikipedia.org/wiki/Tomato, May 9, 2011 (May 12)

Iannoti, Marie, http://gardening.about.com/od/growingtips/AP/Tomato_Tips.htm, May 24, (May 5)

Franklin, Dwight, http://www.ehow.com/facts_6191014_tomato_plant.htmi (May 12)

http://didyouknow.org/tomatoes/ February 8, 2010 (May 12)

http://urbanext.illinois.edu/veggies/tomato.cfm, 2011 (May 12)

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