Soil Amendments and Growing Beans

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Updated on Sep 11, 2013

Could you grow a giant in your backyard? Cansoil amendments--conditioners added to the soil--help yougrow a bigger beanstalk?


Do soil amendments change the growth of a beanstalk?


  • 8 scarlet runner bean seeds
  • Compost
  • Kelp fertilizer
  • Trowel
  • Two large pots
  • Potting soil
  • Watering can
  • Trellis
  • Ruler
  • Tape measure
  • Notebook and paper


  1. Find two places in the garden that have a lot of sunshine. This is where you will plant your bean seeds.
  2. Wait until all danger of frost has passed, then measure out two 2 foot by 2 foot areas for your bean plants. If you don’t have a garden, you can use the two large pots and potting soil. These are your garden plots.
  3. Place four seeds a hand’s length away from each other in the first garden plot.
  4. Add compost and kelp fertilizer to the second garden plot according to the directions on the packages. Use the trowel to gently move this into the soil in the second garden plot.
  5. Place the other four seeds a hand’s length away from each other in the second garden plot.
  6. Create a hypothesis, your best guess about what is going to happen. Do you think that the beanstalks will be the same width? Different widths? Will the plants be the same height? Different heights? Will it make a difference if you add helpful fertilizer and compost to the soil in one of the plots? Now, wait. Watch the seeds come up. Water the seeds whenever the soil begins to get dry.
  7. Once the runner beans are a foot tall, add your trellis behind them so that they can continue to climb.
  8. Once your plants begin to produce beans, it’s time to take out the ruler. Take a close look at each stalk next to the ground. Make sure that you measure each one at about the same height above the ground.
  9. How wide is each stalk? Add the stalk widths of the four plants in the first plot, and then divide by four to get the average. Do the same with the second plot.
  10. Now, use your tape measure to measure the height of each plant. Which ones are the largest?
  11. Did adding fertilizer and compost make a difference? Are the stalks in the second plot giants?


The bean plants with added fertilizer and compost will be larger and taller than the other bean plants.


All plants need light and water to grow, and plants make their own food through a process called photosynthesis. However, even though plants are good at making their own meals, they still need nutrients from the soil to grow. Nutrients such as nitrogen, phosphorus and potassium help plants grow larger, make flowers, and fight off disease. They’re kind of like vitamins for plants.

If your plants grow in poor soil, they may still grow. However, they may not grow as much or make as many big leaves or large fruit. Adding organic fertilizers such as kelp fertilizer and compost helps make nutrients more available to plants. It’s like bringing a whole grocery store of vitamins right to your plants’ roots. This helps the plants grow large and strong, and it helps them grow great veggies.

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