Watering Flower Gardens - U of I Extension

News Release

Watering Flower Gardens

This article was originally published on June 1, 2008 and expired on August 31, 2008. It is provided here for archival purposes and may contain dated information.

Watering is the most often abused gardening practice, said a University of Illinois Extension horticulture educator.

"It seems like gardeners sometimes fall into the traps of too much or too little. Where is the in between?" said Martha Smith. "Understanding how plants use water can help the home gardener find that happy medium."

Water is delivered to plant parts through roots. This means water must be available in the soil. Actually, water is available in the air spaces between the soil particles. After a rain, gravity pulls water out of the largest air spaces and what remains is available to plant roots.

Sandy soils have large air spaces that hold water very poorly. Clay soils have small air spaces that hold water very tightly. Understanding what type of soil you have will determine how often you water. Sandy soils require more watering than clay soils.

"Soil water is used in two ways," she explained. "It is evaporated from the soil surface or it is pulled through the plant into the leaves where it is used for basic life functions such as cooling the plant though transpiration and food production through photosynthesis.

"As water is pulled from the soil by the roots, the smaller air spaces in the soil hold on tighter to the remaining water. The available water is limited and plants have a harder time absorbing it."

Water is supplied to the soil in two ways--Mother Nature or through a garden hose. When not supplied naturally, we have to decide when and how much to apply. How do we determine this?

"There is no set recipe for watering," said Smith. "Look at the plants and take into consideration your soil type and recent weather conditions.

"Look at the plant. A wilting plant indicates a watering problem. But don't always assume it means the plant is dry. Wilting occurs when the turgor pressure within a plant breaks. This can be from lack of water as well as too much water. Always check the soil around the plant. Don't just scratch the surface--poke down four to six inches around the base of the plant."

Weather conditions should also be considered. If it has been hot and windy, sandy soils will need watering more often. Clay soils may be able to hold off for one or two more days before supplemental water is needed.

"Research has shown that one inch of water applied to an average soil will percolate down six inches where the roots are," she noted. "A general rule of thumb is that one inch of water supplied every seven to 10 days during the growing season is adequate for flower gardens.

"Every situation is different and your sandy soil may need water every five days. How do you know when you have supplied one inch of water? Set out measuring devices such as an empty tuna can marked at one inch and turn on an overhead sprinkler. Or if you are hand watering, the experts say five gallons per square yard is about one inch of water."

Smith recommended some other watering tips.

"Water early in the morning through early afternoon," she said. "Late afternoon temperatures increase evaporation so less water will be available for your plants. Avoid watering in the evening. You have a greater chance of disease problems if you allow foliage to be wet at night.

"Water slowly so the soil can absorb it. Avoid a torrential downpour--in nature when this happens most of the water is lost to run-off. Water does not move sideways in soil. You must apply water directly over the area needing it."

Source: Martha A. Smith, Extension Educator, Horticulture, smithma@illinois.edu

Pull date: August 31, 2008