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Self-Watering Planter

In this activity students will explore capillary action and osmosis by making a simple recycled self-watering planter from a pop bottle.

A self-watering planter has four main parts:

  • the plant
  • the soil and pot
  • the reservoir (to hold water)
  • the wick (fabric or string to connect the reservoir to the soil).

Once put together, water will be able to move up the wick and into the soil from the reservoir by capillary action.

The cloth of the wick is made of many tiny fibres with spaces in between, water molecules will stick to each other (cohesion) and stick to the fibres (adhesion) to fill the spaces between fibres.

Water tends to move from areas of more water to areas of less water (osmosis). When water is lost due to evaporation from leaves, it is replaced as plant roots pull water from the soil. In this planter, water is moved into the soil out of the reservoir via the wick.

Definitions:

Capillary action or wicking: the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.

Cohesion: The attraction of water molecules to each other. Water molecules tend to stick to each other in a regular pattern due to the extensive hydrogen bonding. This phenomenon, called cohesion, is easily observed when you carefully overfill a glass with water (by just a little bit!) and observe the water molecules holding together above the rim; this is called a meniscus (eventually, however, gravity overcomes the hydrogen bonds and the water molecules spill down the side of the glass). Likewise, the cohesive property of water allows tall trees to bring water to their highest leaves from underground sources.

Adhesion: the attraction of water molecules to other substances. This is the reason water “sticks” to surfaces and makes things “wet”.the attraction of water molecules to other substances. This is the reason water “sticks” to surfaces and makes things “wet”.

Osmosis: the movement of water from an area with more water to an area of less water, through a selectively permeable membrane.

Evaporation: the process by which water changes from a liquid to a gas or vapour.

Objectives

  • Explore capillary action.

  • Explore the properties of water that allow capillary action to occur.

Materials

  • Per Self-Watering Planter:
    empty clear pop bottle
    scissors
    scraps of fabric (cotton recommended)
    soil (enough to half fill the bottle vertically)
    plants or seeds

Key Questions

  • How does the wick move water?
  • Why do plants need water? What will happen to the plant if the reservoir dries up?
  • Where does the water go?
  • How does capillary action overcome gravity?

What To Do

  1. Using scissors, cut a 2 inch wide strip of cloth as long as your bottle, then carefully cut the pop bottle in half.
  2. Turn the top part of the bottle upside down and sit it into the reservoir. The top half will be the planter and the bottom half will be the reservoir.
  3. Feed the cloth through the hole at the top of the bottle (bottom of the planter), until it touches the bottom of the reservoir.
  4. Holding the cloth upright, carefully fill the planter with a few inches of soil. Curl the remaining cloth into a circle around the planter and cover in soil.
  5. Plant your plant (or seeds) in the planter and fill the reservoir, ensuring that the cloth is sitting in the water. The cloth will now begin its work as the wick, providing a pathway for water to move from the reservoir into the soil.
  6. Place your plant in a sunny location. Re-fill the reservoir with water as needed.

Teacher Tip:

Because of the clear bottle, you will be able to watch the plants roots grow. This is especially interesting with seeds.

Instead of a pop bottle, any set of containers will do as long has you have a hole for the wick and the planter can sit above the reservoir with the wick in place.

Extensions

  • Discuss the water cycle and how it relates to water travelling through this planter and the plant.
  • Design a self-watering planter for a larger plant from recycled materials. Can you use other household items?

Other Resources

Science World | YouTube | Explore a Flower’s Vascular System

Science World | YouTube| Capillary Action:  How to Walk Water From One Cup to Another