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Beeblossom (Gaura) shrubs are a good low water use landscaping choice based on its Plant Factors rating. Photo: Water Authority

Knowing Your Plants’ Water Needs

Landscaping professionals use a resource called the Water Use Classification of Landscape Species (WUCOLS) to classify plants according to their water needs.  

It might sound really complex, but it’s really useful because it breaks down the water requirements for each type of plant into four categories: Very Low, Low, Moderate, and High. These water requirements are also called Plant Factors, and they are an important tool for transitioning to a more water-efficient landscape. 

Water Requirements by Plant Factors 

To come up with a Plant Factor for a given plant, that plant’s  water use is compared to cool season grass in a given climate zone.  

Why is that? Turf is among the thirstiest of all types of plants. When you replace turf areas with climate-appropriate plants with lower water requirements, and irrigate them with more efficient systems, you can realize a tremendous amount of water savings. There is no need to turn your landscaping into a dry, brittle moonscape to do it.  

Here are the Plant Factors, or PF, categories:  

Plant Factor categories from high to low water use. Graphic: Water Authority

Plant Factor categories from high to low water use. Graphic: Water Authority

High: These plants need from 60 to 100 percent of the water needed for a grass lawn (PF of 0.6 – 1.) 

Moderate: Plants need 30 to 60 percent of the water needed for a grass lawn (PF of 0.3 – 0.6) 

Low: Plants need 10 to 30 percent of the water needed for a grass lawn (PF of 0.1 – 0.3) 

Very Low: Plants need 10 percent or less of the water needed for a grass lawn (PF of less than 0.1) 

Group Plants by PF to Irrigate More Efficiently 

In the Water Authority’s Sustainable Landscaping guidebook, plant selections are color-coded to identify their water needs under this system. That approach provides an easy way to group plants by their water requirements in your landscape, so you can irrigate more efficiently.  

This article was inspired by the 71-page Sustainable Landscapes Program guidebook available at The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at   




Here’s How The Largest Dam Removal Project In The U.S. Would Work

No one is popping the champagne corks just yet, but the process to remove four hydroelectric dams on the Klamath River just took a big step forward. On June 28, the Klamath River Renewal Corporation released the Definite Plan for the Lower Klamath Project, a 2,300-page detailed analysis of how the reservoirs would be drawn down, the dams removed, the materials disposed of and the formerly inundated land restored.

San Vicente Aqueduct

1954: Final Pipe Installed for Pipeline 2, San Vicente Aqueduct

Thanks to an intensive lobbying effort and consensus building by the San Diego County Water Authority’s first chairman, Fred Heilbron, the San Vicente Aqueduct’s second pipeline was constructed between 1951 and 1954.

The effort paid off when the second pipeline, parallel to and the same size as the first, began delivering water to the San Diego region. But even the doubling of capacity was insufficient to supply the growing population. The Water Authority had grown to 18 member agencies, and was four times the service area it had when it was originally formed ten years earlier in 1944.

Planning immediately began for a third pipeline, Pipeline 3.