About Watering

The soil is a reservoir for water. The size of the reservoir depends on the extent of a plant’s roots. The wider and deeper the roots spread, the larger that plant’s reservoir. It’s the gardener’s job to ensure that the reservoir doesn’t run dry.

Water Use by Plants

Plants use up water by transpiration, or evaporation from the leaves. As water is transpired from microscopic pores (stomata) on the undersides of the leaves, it is pulled into the roots and up the plant by a force similar to drinking through a straw. The faster the evaporation rate, the more water plants use. Evaporation is governed by the temperature of the air, the relative humidity, and the amount of wind. Hot, dry, windy days require the most water use by plants.

Plants cool themselves in hot weather by transpiring water from their leaves, just as water evaporating from our skin cools us. With adequate water available, a leaf will stay several degrees cooler than a dry piece of paper, even in the sun on a hot day. When water isn’t available, leaves overheat and can scorch in the sun.

Plants also use water flow to transport minerals. Plant nutrients enter the plant dissolved in water and are carried by it to the leaves, where they are used. Without a sufficient water flow, the leaves don’t get the nutrients they need, even if the nutrients are present in the soil. Plants that are too dry for too long begin to show nutrient deficiency symptoms.


Water can be applied in three basic ways: by flooding it over the surface, sprinkling it onto the soil, or allowing it to seep slowly into the soil from drip emitters. Each of these ways has its uses, and a single garden may use all three in different situations.

Gardeners have to decide which method to use, how often to water, and how much water to apply with each irrigation. If you make these decisions properly, your plants will get just enough water all the time. The basic principle for watering is to fill the plant’s root zone each time you water, then let it dry somewhat before watering again.

More than 90% of a plant’s weight is water, so it is vital to replenish what’s lost or used each day. Regular watering is the most important way to maintain healthy plants, particularly under hot summer sun or climates. For best results:

  • Water plants right after planting and frequently thereafter. Whenever the soil just under the surface becomes slightly dry to the touch, its a good time to water thoroughly. In general, most plants prefer soil that is kept moist, not waterlogged.
  • Water deeply so the water fills the root zone. Shallow watering will result in shallow roots, which generally result in unhealthy plants that will not survive hot weather.