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The Effects of Fertilizer on Plant Growth

The Effects of Fertilizer on Plant Growth

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Science Fair Project Description

This science fair project was conducted to ascertain how the amount of fertilizer used will affect the growth of plants. The science fair project involved using levels of fertilizer lower and higher than that which was recommended by the manufacturer.
Complexity level:8
Project cost ($):35
Time required:1 day to prepare, 10 days for the science project experiment
Material availability:Easily found at a plant nursery
Safety concerns:Basic safety requirements


Watering a plant with too little or too much fertilizer will slow down its growth.



Plants need nutrients to grow and fertilizers are a good source of nutrients that may be lacking in the soil. However too much of anything is not a good thing.

Plants absorb water from the soil into their roots through a process called osmosis. This process will require the salt concentration inside the roots to be higher than the salt concentration of the soil. As a result, water molecules will migrate from the soil into the roots in order to equalize the difference in salt concentration levels in the soil and in the roots.

Using too much fertilizer will increase the salt content of the soil. If the salt concentration of the soil becomes higher than the salt content of the roots, water molecules will migrate out of the root into the soil, causing root burn. This will cause the plant to grow more slowly, become dehydrated and eventually die.

Too little fertilizer will cause prevent the plants from growing at an optimal speed due to the lack of nutrients in the soil.

Therefore using the correct amount of fertilizer recommended by the manufacturer is the safest way for the plants to grow healthily.

Scientific Terms

Nutrients, fertilizer, osmosis, molecules


The materials required for this science fair project:
- 1 packet of radish seeds
- 15 plastic pots
- Soil required for  15 pots
- Hasta Gro fertilizer
- Tap water
- Ruler (1 meter)
- 5 plastic containers
- 1 measuring cup


1. For this science fair project, the independent variable is the concentration of fertilizer in the water. The dependent variable is the rate of growth of the radish plants. This is determined by measuring the average height of the 3 plants in each group. The constants (control variables) are the amount of water  and the type of plant used.

2. The 15 pots are filled with the same amount of soil. One radish seed is placed in each pot. (More than one radish seed can be used in each pot in case some of the seeds do not germinate. Once they start to geminate, remove the unwanted plants from the pot)

3. The pots are divided into 5 groups with 3 plants in each group. They are labeled as groups A, B, C, D and E respectively. The pots are watered twice a day according to the concentration recommended below.

a. Group A plants are watered using 33% of the recommended concentration of fertilizer

b. Group B plants are watered using 66% of the recommended concentration of fertilizer

c. Group C plants are watered using 100% of the recommended concentration of fertilizer

d. Group D plants are watered using 133% of the recommended concentration of fertilizer

e. Group E plants are watered using 166% of the recommended concentration of fertilizer

4. The height of the plants is measured on the tenth day and the average is calculated for each group.



It is observed that the plants in group C which were watered at the recommended concentration of fertilizer had the fastest growth in 10 days. The plants in groups A and E which were watered with fertilizers at concentrations that were either too low or too high, had the slowest growth in the 10 days.

The table below records the radish plants' average height (in mm) measured after 10 days.

Plant Group

Fertilizer concentration -100% recommended level

Plant height measure after 10 days (mm)

Average Height (mm)


































The chart below represents the results of our science project experiment.


The hypothesis that watering  plants with  too little  or too much fertilizer will slow down  plant growth, is proven to be true.

Using the correct amounts of fertilizer is important to optimize the yield of our gardens and farms. The continual use of fertilizer will cause nutrients and salt to accumulate in the soil over a period of time. Therefore, using fertilizers once a week instead of daily and having the soil tested regularly for excess fertilizers, is recommended in order to improve the yield and to protect crops.

Also consider

This science fair project may be repeated, this time, with science fair different types of plants like bamboo or beans.

Modify the science project experiment, using different brands of fertilizer.


A great alternative to chemical fertilizers – Hasta Gro organic food plant -

How do the amounts of fertilizer affect plant growth? -

Related videos

Hey there! Here are some awesome videos about this science project that we think you'll really like. They're not only super fun, but they'll also help you learn more about the science behind the project. So sit back, relax, and get ready to have some fun!!
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