The art and science of watering the garden

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Last Updated: 
July 12, 2006

In Oregon, where summers are usually warm and dry, gardens need to be watered. Knowing when and how much to water is a combination of art and science. Oregon State University Extension Service offers some guidelines.

Instead of developing a watering schedule based on calculations and charts, monitor your garden daily to determine watering needs throughout the growing season. Consider your soil, your plants and recent weather.

For example, sandy soil holds much less water than clay soils. Larger plants consume more water than seedlings, but seedlings need more frequent watering. Hot, windy weather dries out the soil. And different plants in your garden will have different water requirements.

Germinating seeds and seedlings need to be kept uniformly moist without being washed away, so water them with a gentle spray every day or two. Developing plants need to be watered deeply, but less often, to encourage deep root growth. Water to a depth of at least 6 inches and then let the surface inch or two completely dry out before watering again.

Frequent, shallow watering keeps roots from growing deep and makes plants susceptible to drought. Over-watering can drown plants by filling up soil pores with water, leaving little or no oxygen for plant roots. Also, excessive watering leaches away nutrients and can contribute to groundwater contamination.

As a general guideline, garden plants that have been watered properly, and therefore have developed deep roots, need a thorough watering every 5 to 7 days in hot weather.

Hand watering delivers water directly to the plants, thus eliminating waste, but it takes time. Spot check to make sure you are delivering enough water, and be careful to give all areas of the garden adequate coverage.

Drip irrigation systems require an initial investment of time and money, but once installed, are convenient and conserve water. You can set up a drip system to meet the needs of individual plants precisely and then alter it throughout the growing season as watering needs change.

Remember that in sandy soil, the water soaks straight down; in clay soil, the water spreads more horizontally. Thus, drip emitters can be placed farther apart for clay soil than for sandy soil.

Sprinklers have the disadvantage of wasting water by watering paths and other open spots in the garden. They also lose water to evaporation and wind drift. Because they wet the foliage, sprinklers also can promote the development of leaf diseases.

If you use oscillating sprinklers, elevate them above the tallest plants so the water streams are not blocked. To make sure all of your plants are watered, place sprinklers so their patterns overlap. Runoff indicates you need to water at a slower rate.

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Author: Peg Herring
Source: Teresa Welch