Science Experiment: How Much to Water Plants?

This science project is great to help any age student or adult to understand how much water plants need!

Setting the Scene: A Big Drink

In most of Florida, the largest percentage of water is used to water farms, orchards, parks, playing fields, parks, gardens, and lawns. All of these forms of watering, from huge agricultural fields to your own back yard, are examples of irrigation. Irrigation simply means watering outdoor areas.

Irrigation ranks high on the list of important water uses. Without irrigation, Florida could not grow most of the crops and fruits we (and the rest of the world) love to eat. We would have fewer fresh and healthful foods. The fruits and vegetables could eat would cost more, and the state would lose a huge part of its economic base. Without irrigation, we could not surround ourselves with beautiful yards, parks, and gardens.

You may have noticed many different methods of irrigation. Some fields have sprinklers that squirt in wide circles; others have sprinklers on large wheels that roll across the fields. Orchards may run water in trenches below rows of trees, or they may have soaker hoses with little holes that allow water to drip slowly to the roots. Homeowners also can select many different kinds of sprinkler systems.

Some irrigation systems use more water than others for the same types of crops. In fact, some irrigation systems use more water than the plants actually need. That extra water is wasted! Since irrigation represents such a huge percentage of our water use, using only as much water as plants actually need can save huge volumes of water. Thoughtful watering also helps homeowners spend less money for water, too.

The Basic Science: Dripping at the Roots

Plants get most of their water from the soil. Their roots draw water out of the soil and pull it up to their stems and leaves by using capillary action. You can observe capillary action by hanging a paper towel over the edge of a basin of water. Within a few hours, some of the water will climb up the towel and flow over onto the countertop.

A similar thing happens to the roots of plants. In most plants, the roots extend deep into the soil. If the water is near the surface, the plant’s roots may grow upwards to reach it. Those roots tend to dry out more quickly than deeper roots, so they need more frequent watering.

Every plant has different watering needs. Watering according to those needs uses less water and makes healthier plants. In addition, most plants prefer water at the root system rather than the leaves.

Homeowners can also save water by choosing native plants, which are plants that originally grew in areas with climates similar to ours. Those plants are well suited to the Florida sun, heat, and rainfall patterns. They also use less water than plants brought in from wetter, drier, or cooler climates.


Here is a list of several widely used techniques for saving water used for irrigation. Many of these tips are based on the need to keep the water you apply from evaporating, because evaporation causes a great deal of water loss in hot climates like ours. (Of course, a great way to save water in the garden is to grow plants that require less water.)

  • Water no more than 2 days a week in the summer, and less often in cooler, rainier weather.
  • Grass usually requires more water than ground covers and gardens; keeping grass higher than 1/3 inch keeps roots shaded and less thirsty.
  • Mulch spread around plants’ root systems keeps water from evaporating as quickly.
  • “Water before 10 a.m. or after 4 p.m.” Watering in the morning and evening reduces water lost to evaporation.

You can do a series of experiments to discover your own wise gardening methods and then prepare water-saving tips for others.

Overview of Project

Select several different types of plants that have different watering needs, and grow each of them in different conditions.

Suggested Materials

  • 4 each of the following plants in equal-sized pots: impatiens, geraniums, jade plants, cacti
  • Optional: shade-tolerant and grass-tolerant grass seeds planted in trays
  • Watering can
  • Measuring cups
  • Labels


  1. Select a shade-tolerant plant that needs plenty of water, such as an impatiens; a plant that likes full sun, like a geranium; a plant with succulent leaves, like a jade plant; and a drought-tolerant cactus. The staff at a garden store can help you select appropriate plants. You may also grow trays of several types of grass that require different amounts of water. Again, a garden store can help select appropriate grass seeds.
  2. Set up four pots for each plant. If you are growing grasses, set up as many trays as you have types of grass. All pots and trays should be the same size and filled to the same level for purposes of comparison.
  3. Use recommended soil. For example, the impatiens, geranium, and grass should have potting soil with some organic material. Look for cactus soil for the jade and cactus.
  4. Label each of the pots for each plant variety “A,” “B,” ‘C,” and “D.”
  5. Carefully measure and record the amount of water you give to each plant throughout the duration of your experiment. Water the plants in this manner:
  • Pot A: Twice the recommended amount
  • Pot B: The recommended amount
  • Pot C: One-half the recommended amount
  • Pot D: One-tenth the recommended amount

    Develop a recording system to track how often you water and how much water you apply, and to write your observations about how the leaves appear and how the soil feels.

   6. Plot and analyze your results.

   7. Draw conclusions about each plant type’s water needs.

  • Which type of plant would work best in a Florida garden or yard?
  • What could you do to ease a water thirsty plant’s water demands if you planted it in a garden?
  • What happened to the plants that received too little water?
  • What happened to the plants that received too much water?


Use mulch on the plants. How does that vary your results?

Experiment with different shade conditions.

Compare results if you water at the roots or water through the soil. You could push a straw into the soil to the level of the roots, and apply water through the straw so the water goes directly to the roots.

Grow plants with soil in clear plastic cups to observe their root systems. Set up an experiment in which you water one set of plants frequently with small amounts and another set less often but with enough water to soak to the bottom of the cup.

Putting it Together

Make a visual display that demonstrates how plants need different amounts of water. Add a “Water Saving Tip Sheet” for home irrigation.

Draw a landscaping plan for a garden. Research drought-tolerant plants through some of the sites below.

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