From the desert cactus to the rainforest fern, plant species vary in their water
requirements. But all plants need at least some water. Plants draw most of the water they need up from their roots into
the stems and leaves. (Many plants can take in small amounts of water through their
leaves.) Plants use water in several ways.
1. Water is required for photosynthesis, the means by
which plants manufacture their food. We’ll cover the details of photosynthesis next
week—for now let’s just say that water is required for photosynthesis, and that
green plants must be able to photosynthesize to stay alive.
2. During photosynthesis, some water is lost through
evaporation through the stomata, the pores on the undersides of the leaves. This
evaporation helps cool the plant—similar to the way our perspiration cools our bodies
as it evaporates.
3. Water is required to keep plant cells turgid—full
of fluid—keeping the structure rigid and the leaves opened to the 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.
Every garden’s soil is unique, and soils can vary
even within a small yard. It’s helpful to become familiar with your soils, so you can
begin to develop a sense of when your plants will require supplemental watering.
What are some symptoms of too much or too little water? A
wilted plant indicates something is wrong. A number of things can cause a plant to
wilt—insufficient water, too much water, intense light or heat, and disease. (There
are 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 causing the wilting.
Unfortunately, water problems aren’t always easy to
identify. Here are a few guidelines for houseplants—but remember, these aren’t
definitive! Get to know your individual plants so you can "read" their symptoms.
