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Irrigation Basics

Most Oklahomans are very aware of the need to add supplemental water to lawns and gardens year round, but especially during our hot, windy, and often dry, summers. How much water a plant uses depends on the plants genetic makeup, the amount of sun and wind it receives, the type of soil and how much fertilizer is applied.

Water demand increases in plants grown in sandy soil. Also fertilized plants usually put on more foliage and growth and need more water. Wind and low humidity increases plant water loss through "evapotranspiration", or loss of water from both leaves and soil.

Choosing Plants: Plants which naturally use less water are often used to design a garden with low water usage. These garden beds are called  "Xeriscape Gardens". Two useful references for xeriscaping and plants to consider are in the two OSU references listed below.

Plants which have lower water requirements generally are slow growing, small, have narrow leaves and leaves often are modified to include waxy coating, hair and reduced pores from which water is lost. Many are gray in color.

L-333 Xeriscape plants.pdf

L-332_Xeriscape__Demostration_Garden.pdf   

How to Irrigate: Many homeowners use a garden hose with a spray nozzle or sprinkler head for irrigation. Others have in-ground automated sprinklers or drip irrigation systems. They all will deliver the needed water, but each has its positives and negatives.

  • Hand watering with hose and attachments is less expensive, but more labor intensive and easier to forget. With an adjustable nozzle, one can direct the water to areas needing irrigation more effectively than with systems using sprayers. It also gets one into the garden where problems with disease or insects may be spotted.
  • In-ground systems are much more expensive, but will deliver a set amount of water into the spray zones predictably. These do a great job of irrigating lawns, but are more wasteful of water because of evaporation  and water run-off from excessive application rates. Water running down the curb is a common sight from these systems.
  • Drip irrigation has much going for it. The components are relatively cheap, easy to install to outdoor faucets and require some simple tools for installation. There is little or no digging involved. Most companies selling these components have very useful manuals to use as a guide.

Drip, or trickle irrigation delivers water to the root zones of plants where it is needed. The supply tubing is usually covered with mulch and there is little evaporation or run-off. There are many attachments used in drip-irrigation, but one of the more useful ones is the pressure regulating emitter. These cheap attachments allow a constant amount of water to be delivered to a plant's root zone regardless of the water pressure.

Regardless of which method you use for irrigations, there are some guidelines which are useful to follow.

  • Depending on the season, most plants need from 1-2 inches of water per week; either by rainfall or irrigation.
  • Plants (including lawns) should always be watered in the morning. This allows the leaves to dry before nightfall. Nighttime is when fungal diseases grow best. When hand watering, spraying the root zones keeping  leaves dry helps reduce disease.
  • Deeper, infrequent watering is much better for plants. This encourages deeper root growth and is associated with less water loss due to evaporation.
  • The effect of adding mulch to the garden area cannot be over-emphasized. It greatly reduces water loss and water needs by all plants by cooling the soil and lessening evaporative losses.

 
BAE-1511: Drip (Trickle) Irrigation Systems

L-346: Responsible Lawn Care  

Irrigation System Planning and Management, University of Missouri

The Oklahoma Mesonet is an excellent resource for information about recent rainfall, soil moisture and evaporative losses. In the "SIP" section (Simple Irrigation Plan), there is information to help one decide how much and when to irrigate. It will also help one calculate the cost of irrigation.

Oklahoma Mesonet SIP