Science project

Plant Neighbors: Friends or Foes?

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Research Questions:

  • What resources do plants compete for?
  • What are some examples of plant adaptations?
  • How can people use their knowledge of plant adaptations to grow better crops?
  • What is companion planting?
  • What bio-chemicals or plant hormones do plants use to “communicate” with each other or compete with one another?
  • How do you care for plant seedlings?
  • What variables should be considered when performing this experiment?
  • What is it important to have a ”control” in the experiment? What will the control be in your experiment?

Gardeners and farmers have been using companion planting techniques for many years to grow healthy crops. Companion planting is a method of arranging different types of plants together in a way that will allow them to grow harmoniously, prevent pest damage, and in general use each plant’s particular adaptations to assist their neighboring plants. Plants can release chemicals into the soil that can be beneficial or harmful to their neighbors. They may deter pests that are harmful to their neighbors. In a sense, plants “communicate” through chemistry.

Recent research has taken the study of how plants interact with one another a step further finding that two plants, Jewelweed and Sea Rocket, grow better with their siblings that with other plants. These two examples will actually grow in a way that allows them to share resources with one another rather than compete for resources like they would when growing near other plants. The plants “communicate” through their roots.

Understanding adaptations like this chemical communication is an important way to understand the interconnections in ecosystems. When we better understand and appreciate the complexity of these interconnections we do a better job of caring for the environments we live in. Understanding these adaptations of plants allow us to produce food in healthier ways and take an active interest in the natural and human built environments that we live in.

All materials are available at a garden center, hardware store or greenhouse.

  • Carrot seeds
  • Lettuce seeds
  • Dill seeds
  • 5 seed starter trays
  • Potting soil
  • Sunny counter, greenhouse or cold frame
  • Water
  • Graduated cylinder, or measuring cups
  • Popsicle sticks
  • Ruler or measuring tape
  • Camera (optional)

  1. Read the planting information on your carrot, dill and lettuce seeds.
  2. Fill the seed starter trays with soil.
  3. You will plant lettuce seeds in the first tray based on the planting instructions. Mark the tray by inserting a popsicle stick labeled “Lettuce” in one of the cups.
  4. Plant dill in the second tray based on the planting instructions. Mark the tray by inserting a popsicle stick labeled “Dill” in one of the cups.
  5. Plant carrot seeds in the third tray based on the planting instructions. Mark the tray by inserting a popsicle stick labeled “Carrot” in one of the cups.
  6. The first three trays you planted are the controls for this experiment. Place these three trays apart from one another in three locations that receive fairly equal amounts of light.
  7. You will plant dill seeds and carrot seeds together in the fourth tray. Label the tray with a popsicle stick that says: “Dill/Carrot”.
  8. You will plant carrot and lettuce seeds together in the final tray. Label it with a popsicle stick that says: “Lettuce/Carrot”.
  9. Once you have planted your seeds you will carefully keep observations as they grow. Along with your observations and measurements you will keep track of when and how much water you give them. Use the graduated cylinder or the measuring cups to measure the water. Develop a consistent plan for how often and how much water you will give your plants.
  10. Keep track of your observations using a table like the one below. (Table 1) You may also wish to take photographs of your plants on a regular basis, or sketch careful drawings of them as they grow.
Table 1
Plant Tray #
Amount of water

Observations (height, leaf number, color, etc.)

Terms/Concepts: Variable; Control; Plant Adaptations; Companion planting; Germination; Organic gardening; Biochemistry; Plant hormones


Author: Sarah Benton
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