Science project

Pruning Tomato Plants


  • 4 tomato seedlings of a similar variety
  • 2 planters
  • 4 tomato cages
  • Potting soil
  • Watering can
  • Notebook and pencil


  1. Create a hypothesis, your best guess about what is going to happen. Will tomato plants grow more tomatoes if the lower stems are removed?
  2. For this experiment, you’ll need two planters and four tomato cages, which act as a trellis to support the tomatoes as they grow. When it’s nice and warm outside and all danger of frost is long gone, fill up your planters with high-quality potting soil and plant two tomato plants in each one. Water them regularly. Tomato plants love water.
  3. As your tomato plants begin to flower, look at where the flowers appear on the plant. There will likely be a few stems with leaves on them below the first stem that has flowers.
  4. Ignore the flowers and leaves on the tomato plants in the first planter. Prune the plants in the second planter. To do this, look for the first stem with flowers on it. Look at the stems below that. If they show no sign of flowering, gently remove them.
  5. You can also take a look at the flowering stems. If you see little side stems coming from the central stem which don’t have flowers on them, you may also remove those as well.
  6. As the tomatoes begin to set fruit, make sure that you water them a lot and keep them in the warm sun. When the tomatoes set fruit, count the number of fruits that come off each tomato plant. Write this down in your notebook.
  7. At the end of the season, compare notes.  Which tomato plant had the most tomatoes? To find out, add up all of the tomatoes produced by the plants that were not pruned and divide by two to get the average. Do the same with the number produced by the plants that were pruned. Did one planter produce more tomatoes than the other? Why?


The tomato plants that were pruned will usually produce more tomatoes than the ones that are not pruned.


A plant’s goal in life is to reproduce, and it does this by creating seeds. Tomato plants store their seeds in tomatoes, so it would seem like it would be best for each plant to produce as many tomatoes as possible.

Why does pruning tomatoes tend to result in more fruit? There are many factors that go into fruit production.

Plants need to make their own food. They do this through photosynthesis, a process of making food from light, water, and carbon dioxide. Plants absorb sunlight with their leaves, so they need leaves to make food and grow.  When you prune a plant, you remove some of its leaves that make food. However, you also remove leaves that might provide shade to the branches with the fruit on them, increasing sunlight to the rest of the plant. This is good for photosynthesis.

Pruning a plant can also put it under moderate stress. When plants are somewhat stressed, they can produce more flowers and fruit in an effort to reproduce themselves.

There are many different factors that determine how much fruit tomato plants can produce. Pruning is just one way to help your plants grow more fruit. If you find that your plants didn’t produce a lot of fruit, they might need to be in a sunnier area. Experiment until you find the best place for growing your delicious tomatoes!

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