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Companion Planting with Symbiosis and Systems

Students explore a garden to find symbiotic relationships and think about the functions that plants can provide.

Companion Planting with Symbiosis and Systems

· To simplify this exercise, ask your student to work in pairs.


Possible Functions of Plants (Discussion and Station A):

· cool down environment · fix nitrogen · restore soil · pull nutrients from deep soil to topsoil · break up clay soil · medicine · repel pests · building materials for us and other animals (like birds’ nests) · to be eaten · attract animals · insects · birds · lizards · snakes · prevent invasion by weeds · generate mulch naturally or when trimmed down · to prevent erosion · to purify water · to screen an unwanted view · to block wind · provide shade · slow a fire

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When two living organisms, such as plants, live together, it is called “symbiosis.” The focus in this activity is about companion planting, which is really the study of beneficial symbiotic relationships among plants.

Students practice companion planting to predict the outcome of an experiment and troubleshoot problems with designing a garden when plants can be either beneficial or harmful to one another.

There are many ways that plants affect each other. Here are a few:

Better Growth  Some plants simply grow better around certain plants, and not as well with others. No one yet knows the exact science of why. Example: Green beans grow well with strawberries. Bibb lettuce grows well with spinach.

Nutrition  In the plant world, there are “heavy feeders” and “heavy givers.” Heavy feeders are plants that take and keep a lot of nutrients from the soil as they grow. A lot of the plants we love to eat (tomatoes, lettuce, corn, and squash to name a few) are heavy feeders. Heavy givers, on the other hand, are plants that give back a lot of nutrients to the soil. Nitrogen-fixers or legumes such as peas, beans, alfalfa, clover, and vetch are examples of heavy givers. After growing heavy feeders in a particular area, it’s a good practice to plant heavy givers to restore the soil.

Accumulators  Many wild plants including those we consider “weeds” play a vital role in the plant community as doctors and healers of soil. Many weeds either collect trace minerals from the soil for future fertilization or remove harmful elements from the soil. Example: pigweed, lamb’s quarters, and thistles have deep roots to bring up minerals from the lower soil, which they hold in their stalks and leaves. When they die and decompose into the topsoil, these minerals become available to crops with shallower roots.

Pest Control – Some plants give off chemicals from their roots or leaves. Example: certain kinds of marigolds release a chemical from their roots that are absorbed by plants around them. When whiteflies come to suck on the leaves of those plants, they think they are eating the bad-tasting marigolds and they leave.

Physical Many plants have a special need for sunlight or shade. One plant can help provide these conditions for another. Example: Lettuce plants like to nestle among other taller plants for shade.

Pollinator Attractors  Many plants reproduce with the help of beneficial insects and other pollinators. By putting plants that pollinators love in your garden, you will help the other plants as well! Example: Bees love hyssop, thyme, catnip, and lemon balm. Once you bring bees into the garden, they will help pollinate everything.


Types of Symbiotic Relationships:

Mutualism is a mutually beneficial relationship in which both organisms benefit. Each individual provides an advantage to the other, enabling them to exploit each other and thereby enhance their chances of survival.

Example: Corn and beans – The corn provides a tall structure for the beans to climb and the beans pull nitrogen from the air and bring it into the soil for the benefit of both of them.

Commensalism is loosely defined as a symbiotic relationship in which one organism benefits and the other is unaffected.

Example: Sage plants produce an odor that repels carrot flies. If planted by carrots, the carrots benefit while the sage plants are unaffected.

Parasitism is a relationship that is beneficial for one organism and harmful for the other.

Example: Mistletoe, a plant that parasitizes trees, has roots that penetrate the tree bark, capturing nutrients from the tree, but damaging the tree’s own protective layer.



Students discover which plants have symbiotic relationships and how this impacts each organism. They identify three general types of symbiosis: mutualism, commensalism, and parasitism. Students see the interconnectivity between different plants and animals and their environments. Many relationships between organisms are complex and involve multidirectional interaction.



CCSS: 7.W 4: Produce clear and coherent writing

7.SL 1: Engage effectively in a range of collaborative discussions with diverse partners

NGSCS: LS1.A: Cells work together to form tissues and organs with a function

LS2.A: Organisms and POPs are dependent on their environment. Interactions with biotic and abiotic things.

LS2.A: Mutualism, Commensalism, Parasitism

PS2.C: Patterns of change and an understanding of feedback mechanisms are used to predict a system’s future


NGSCS Cross-Cutting Concepts:

1. Patterns: Macroscopic patterns are related to the nature of microscopic and atomic-level structure.

4. Systems and System Models: Models can be used to represent systems and their interactions such as inputs, processes and outputs- and energy, matter, and information flows within systems.



· 1 clipboard or field notebook per student

· 1 copy of Companion Planting Guide per group

· 1 Station Packet per student (includes the directions for stations A-C)

· Enough table space outside for groups to gather



· Within a garden, plant one set of companion plants close to one another and another set farther away from each other on the same day (carrots and leeks are great for fall; other examples can be found in the Companion Planting Guide). Hopefully, when brought together, the plants are growing visibly healthier or bigger than the other plants which are separated.

· Have four stations prepared outdoors by the school garden. For student comfort and efficiency, the area should have some shade for hot days and a tabletop bench for writing.

· Each station should have printed titles and directions.

· Provide each student with worksheets.

· Label the companion plants with the plants’ names.

· Label the Station B Experiment visibly so that the students can find the Station B Experiment.



1. Start with a Think-Pair-Share activity. » Ask students to individually think about the following question: What are some examples of symbiosis in the animal world? (one minute). » Have students form groups of four to have them discuss their thoughts with the other students. » Now discuss as a class (up to five minutes).

2. Assign groups to a station A-C and have them rotate every 10 minutes.

3. As the students explore the garden, use Exploration Questions provided in the Appendix to guide them.

4. After rotating the students through the stations, return to the classroom.



1. The class can share their garden bed designs.

2. Students can discuss the possible functions of plants (see the Companion Plant Guide for possible answers).