Hydrozoning

There is very little research material on the actual water requirements of landscape plants. Plant water requirement knowledge is complicated by variables such as location, soil, exposure and other factors.

Hydrozone definitions refer to water requirements of the plant species. Average rainfall in Colorado Springs during the growing season is 13.2 inches. Supplemental irrigation refers to water added above average rainfall. Supplemental irrigation requirements vary depending on seasonal conditions. For example, an unusually dry July may increase the need for supplemental irrigation, while a very wet July would bring it down.

• Very Low Water Zone
  Infrequent or no supplemental irrigation is required after the plants have become established. This rather strict definition limits the plant selection to mostly native species with the addition of plants with the proven ability to adapt.
• Low Water Zone
  Limited supplemental irrigation is required on an occasional or periodic basis depending upon the rainfall, the season, the type of plants and their location. The plants in this zone need approximately 10 percent to 25 percent of the irrigation requirements of turf, or 4 to 12 inches of supplemental water added. As an illustration, water on a two to three week schedule rather than on a two to three day schedule.
• Moderate Water Zone
  Supplemental irrigation is required on a regular basis, depending upon the rainfall, the season, the type of plants and their location. A moderate water zone allows the use of more water intensive plants in the landscape. For example, many introduced ornamental plants belong in this group. The type of plants in this zone can vary over a wide range, and it is difficult to give an estimate of the water requirements. As a rough guide, we'll say a minimum of 25 percent to 50 percent of the turf requirements, or 12 to 25 inches of supplemental water.
• Turf Zone
  Turf is the most water-consuming element in the landscape and should be located and irrigated separately from other areas. Turf should be limited to those areas where it has a functional use. The total water requirement for bluegrass turf is about 40 inches per year for most locations and applications in Colorado Springs. That equals about 25 inches of supplemental irrigation if we have a 'normal' rainfall season.

All plants require supplemental irrigation until they become established. This may extend over a period of two to five years. The recommendations above are based on the assumption that a reasonable attempt has been made to follow the Xeriscape principles. These principles include the addition of ample organic materials to existing soil and the use of an organic mulch to retain soil moisture. The use of all the hydrozones may not be practical in a small residential landscape. The important thing is to separate turf from other areas and to group plants with like water requirements together. See example shown below.

Finally, know your landscape. Let the plants be your guide rather than watering on a fixed schedule.

Back to Step 5: Master Planning.