• Lavender shrubs require very little water to thrive.Anna Yu/Photodisc/Getty Images
  
  Shrubs require watering before they begin to wilt or show other signs of drought stress. Once the plant is under stress, it becomes more prone to insect or disease damage. Providing the proper amount of moisture, whether from irrigation or natural rainfall, helps ensure the plants remain healthy and attractive.
  
  

Soil Types

• The type of soil in the shrub bed affects how much moisture remains in the plant's root zone. Sandy soils drain more quickly, retaining little water, so these soils must be watered more often. Heavy clay soils tend to absorb too much water, becoming soggy easily, so they require less water. The best soil for most shrubs is high in organic matter so that it doesn't drain too quickly or slowly. When possible, work organic matter such as compost into the soil before planting, or plant shrubs in a raised bed if you have poor soil.
  
  

Plant Needs

• Shrubs vary in drought tolerance. Some shrubs, such as sage or lavender, are highly drought tolerant and rarely need supplemental irrigation. Most ornamental shrubs require a moderate amount of water and do not tolerate extended dry periods. Shrubs that flower throughout the summer or produce fruit typically need weekly irrigation to remain productive. In most cases, new plantings require more water than existing mature plants.
  
  

Watering Amount

• Except for drought-tolerant shrubs, provide the plants with approximately 1 inch of water a week from irrigation or natural rainfall throughout the growing season. Water at the base of the plants when possible, as this allows the water to penetrate the root zone instead of evaporating. Early morning irrigation also helps prevent water loss from evaporation. Water drought-tolerant shrubs during extended hot, dry periods, usually no more than once every 10 to 15 days.
  
  

Checking Moisture Levels

• Verify that shrubs are receiving enough water by checking the soil moisture after each irrigation. One inch of water moistens the top 6 to 12 inches of soil. Check by digging a small hole near the base of the shrub and feeling the soil by hand, or by using a tensiometer. The tensiometer measures soil moisture when inserted in the soil near the shrub. The shrubs need water when the meter reads between 50 and 70 centibars. Shrubs are properly watered when the meter reads between 5 and 15 centibars the day after irrigating.