From Seed to Seed:
Plant Science for K-8 Educators

 

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    Water

From the desert cactus to the rainforest fern, plant species vary in their water requirements. But, as with light, all plants need at least some water.

Plants draw most of the water that they need up from their roots into the stems and leaves. In addition, many plants can take in small amounts of water through their leaves. Plants use water in several ways. Most importantly, water is required for photosynthesis to take place. During photosynthesis, some water is lost through the stomata. This evaporation helps cool the plant-similar to how our perspiration cools our bodies as it evaporates. Finally, water is required to keep the plant cells turgid-full of fluid-keeping the plant's structure rigid and the leaves open to sunlight. When water is lacking in the plant, this structure weakens and the plant wilts.

Since most plants draw water from the soil, the amount of water in the soil is important. One factor affecting water availability is soil type. Gardeners with very sandy soils know that their soil drains quickly, and they must water frequently during dry spells. Heavy clay soils, on the other hand, retain water and are often poorly drained. Most soils can be improved over time, especially with the addition of organic matter.

What are some symptoms of too much or too little water?

Unfortunately, water problems are not always easy to identify. Although a wilted plant does indicate that something is wrong, a number of things can cause a plant to wilt-insufficient water, too much water, or intense light or heat. There are even a number of "wilt" diseases that affect a plant's ability to absorb water. If a plant is wilted even though the soil is moist, don't add any water. Something else is probably causing the wilting. Here are a few guidelines for your indoor classroom plants-but remember these aren't definitive!
  • Some plants will notify you that they desperately need water by dropping their older, lower leaves. These leaves will turn bright yellow before dropping. In this way, plants sacrifice their older leaves to ensure that the new growth gets the water it needs.

  • If new growth is dropping, or has brown leaf margins, the problem might be too much water.

It is a little bit more difficult to diagnose water problems in the schoolyard garden. Wilting may or may not indicate a lack of water. And scorched leaf margins can indicate any number of problems. The best thing for you and your students to do is to get to know your plants and their water requirements!













 

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