Posts

An example of drought tolerant landscaping with low water use plants. Photo: Kelly M. Grow, California Department of Water Resources landscape conserve

How Much Water Can Your New Landscape Conserve?

Landscape designs using the least amount of potable water necessary are greatly encouraged in arid or Mediterranean climates like in San Diego County. It’s an important motivation for homeowners to consider efficiency and sustainability to lower water use, saving a precious resource.

Maximizing your landscaping’s ability to capture and use natural rainfall can also help reduce or even completely eliminate your reliance on potable water for irrigation.  Compare how much water your new landscape design will need against your existing landscaping’s water use. You’ll be able to estimate your future water savings.

Start by calculating the water use requirements of landscaping filled with plants that require high amounts of water, or moderate amounts, low or very low water requirements.

In these examples, evapotranspiration (ET), irrigation efficiency, and landscape area are exactly the same. The only difference: our examples are home to plants with different water requirements.

How to calculate your landscape’s water use

To calculate water use, you can refer to the San Diego Water Efficient Landscape Ordinance for guidance. Go to www.sdcounty.gov and search “Landscape Ordinance.” The four key variables are:

  1. Landscape Area (LA) – the square feet of area being landscaped with plants that require irrigation
  2. Evapotranspiration (ET) – this is the number in inches based on your San Diego Climate Zone
  3. Plant Factor (PF) – This is moderate, low, or very low depending on the plant selection
  4. Irrigation Efficiency (IE) – There is no such thing as a perfect irrigation system. Many factors can limit efficiency and impact your water use and the health of your plants.

Use a landscaped area of 1,000 square feet, with an ET of 51 inches annually, and IE of 0.7. Look at the big difference your plant selection can make in your water use.

Example 1: High Water Use plants (PF = 0.8) – 36,137 gallons of water per year

Example 2: Moderate Water Use plants (PF = 0.5) – 22, 586 gallons of water per year

Example 3: Low Water Use plants (PF = 0.2) – 9.034 gallons of water per year

Example 4: Very Low Water Use plants (PF = 0.1) – 4,517 gallons of water per year

From the highest estimate to the lowest estimate, you could potentially save 17,103 gallons of water every single year.

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

Knowing how to classify your plants by water use characteristics will help you plan your sustainable landscaping. Photo: Water Authority plant factor

Know Your Plant Factor Water Requirements

Landscaping plants have different water needs. The water requirement of each plant in your landscaping can be determined by gathering information about the plant and then comparing it to the amount of water needed by the cool-season grass growing in your climate zone.

Take a tip from landscaping professionals. They use a resource called the Water Use Classification of Landscape Species to classify plants according to their water requirements, called Plant Factors.

These water requirements divide plant species into four categories: Very Low, Low, Moderate, and High.

When you are selecting plants for your landscaping, use the classification to choose low water use plants for your landscaping. You can also use it to group a handful of higher water use plants together if you want to indulge in a few favorites.

When you have decided on your plant palette and placement, you can now figure out the water use of your entire landscape area. This will help you plan out your artificial irrigation.

Factor in watering requirements

Determine water use before choosing plants for your new sustainable landscaping. Photo: San Diego County Water Authority

Watering needs for landscape plants use a measuring stick based on cool-season turf. It’s because cool-season turf is extremely thirsty.

When you replace turf areas with climate-appropriate plants that use less water and irrigate them with more efficient systems, you can conserve a tremendous amount of water. You don’t need to turn your landscaping into a dry and dusty area to do it.

High Plant Factor: Plants needing 60 to 100 percent of the water needed for a grass lawn (PF of 0.6 – 1.)

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

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

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

Irrigate More Efficiently By Grouping Plants

According to the San Diego County Water Authority’s Sustainable Landscaping guidebook, plant selections are colored-coded to identify their water needs under this system. It gives you an easy way to group plants by their water requirements in your new landscaping, so you can irrigate them more efficiently.

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

Match Your Climate Zone to Your Landscaping Plan

Making smart decisions about your landscape design and your plant choices relies in large part on your climate zone. San Diego County’s six different climate zones vary in their average conditions. By choosing wisely, you can minimize the need for artificial irrigation and still create a beautiful, sustainable landscape. The California Irrigation Management Information System divides San Diego County into these six climate zones: Coastal, Coastal Inland, Upland Central, Transition, Mountain, and Desert.

Homeowner Jeff Moore's back yard zen garden featuring his landscape work fit beautifully into his area's climate zone. Photo: Water Authority climate zone

Match Your Climate Zone to Your Landscaping Plan

Making smart decisions about your landscape design and your plant choices relies in large part on your climate zone. San Diego County’s six different climate zones vary in their average conditions. By choosing wisely, you can minimize the need for artificial irrigation and still create a beautiful, sustainable landscape.

The California Irrigation Management Information System (CIMIS) divides San Diego County into these six climate zones: Coastal, Coastal Inland, Upland Central, Transition, Mountain, and Desert.

This climate system provides you factors to help you understand which plants will thrive in your landscaping under its native conditions. Gardening in harmony with your local climate zone and your microclimate helps you use resources, including water, most efficiently.

Descriptions of San Diego’s six climate zones

Which CIMIS climate zone are you in?

San Diego County's geography falls within six of the 24 CIMIS climate zones. Photo: CIMIS match your climate zone

San Diego County’s geography falls within six of the 24 CIMIS climate zones. Photo: CIMIS

Zone 1: Coastal Prairie

The Coastal Prairie zone hugs our county’s coastline. It is the zone most strongly influenced by the ocean, with a mild marine climate resulting from the warm Pacific Ocean. Winters are mild, summers are cool, and there is almost always moisture in the air.

Zone 4: South Coast Inland

South Coastal Inland areas are just inland from the beach, or on high bluffs above the coastline. You can feel the ocean breeze, but you can’t taste the salt in the air. There is less fog and humidity than the immediate coastal area, and higher temperatures.

Zone 6: Upland Central

The higher elevation Upland Central areas are influenced both by moist coastal air and dry interior air. Humidity, morning fog, and wind are moderate, with low annual rainfall.

Zone 9: Transition

This marine-to-desert transition climate is farther inland. It features a combination of warmer thermal belts and cold-air basins and hilltops, with an occasional marine influence. The climate can vary from heavy fog to dry Santa Ana winds.

Zone 16: Mountain

Steep slopes, variation in sun and wind exposure, shallow soils and heavier rainfall affect plants in the Mountain regions. Average annual rainfall is 30 inches, and wet years can bring 45 inches or more.

Zone 18: Desert

Dry and hot daytime conditions combine with cold nighttime temperatures in the Desert zone. Humidity is very low, and water is scarce. Average annual rainfall can be as low as 2.5 inches, with an average of just 6 inches.

Learn more about the specifics of your climate and microclimate on the California Irrigation Management Information System website.

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.