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Choose your landscape plants carefully to reduce your water use. watering your plants

One Simple Key to Watering Your Plants

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When you’re replacing your landscaping with an eye to conserving water, it’s important to understand how much water plants really need. A quick, simple way landscape experts do this is a method the home landscaper can use, too.

Evapotranspiration (ET) is the process of assessing various factors to determine how much water plants use, and when they need it. ET explains and incorporates important environmental conditions such as solar radiation (sunshine) or cloud cover. The stronger the sun’s rays, the higher the ET.

Plant leaves work a lot like mini solar panels. Leaves gather energy plants use to transform water and carbon dioxide from the air into oxygen and sugars for growing.

Transpiration of moisture through leaves is similar to perspiration. It cools down the leaves. Water also evaporates from the soil itself around plants. The combined water loss from the plants and the soil together makes up evapotranspiration.

Understanding water loss in terms of ET helps you select the right plants for your sustainable landscaping by assessing your overall landscape water requirements, planning irrigation, and managing the Soil Moisture Account.

Drought Tolerant Plants Share Four Common Qualities

Plants with silver, leather-like leaves like this Agave are extremely water efficient. Photo: Charlie Neuman watering your plants

Plants with silver, leather-like leaves like this Agave are extremely water efficient. Photo: San Diego County Water Authority

Do you need help identifying climate-appropriate plant choices for your new sustainable landscaping? Look for these four characteristics shared by drought-tolerant plants.

Stiff, Leathery Leaves: These leaves hold and store water, and stay evergreen most of the year.

Silver or Hairy Leaves: Light-colored leaves reflect sunlight to cool the plant. Hairy leaves hold moisture longer, and also protect the plant from hot direct sun.

Tiny Leaves: Tiny leaves are tiny solar panels. Lots of tiny leaves are easier to keep cool than a single larger leaf because there is more surface area to receive energy and use evaporation to cool down.

Solar Tracking Leaves: Some plant leaves are sun worshipers. They will turn toward the sun’s path throughout the day. As the day progresses, you will see the leaves more horizontally oriented. The plant is shifting its solar panel leaves to minimize sun exposure. Many California native plants like manzanitas have this ingenious adaptation.

The Water Authority’s Sustainable Landscaping guidebook contains a Plant List with climate-appropriate plants. They are also highlighted throughout the guidebook.

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.

Fruit trees, especially citrus, thrive in San Diego County’s climates with just a little bit of care. The Pineapple Guava (Acca sellowiana) is a good choice with spectacular blooms. Photo: WIkimedia/Creative Commons License Edible Plants climate zone

Sustainable Gardeners, Get Into Your Climate Zone

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People around the world know San Diego for its beautiful, sunny, and mild weather. San Diego residents know our daily weather has more variety than visitors might imagine.

Climate is defined as the average weather conditions in an area over a long period, generally 30 years or more. German climate scientist Wladimir Koppen first divided the world’s climate into six regions in the early 1900s.

Since then, U.S. climate zones have been defined in more detail. The U.S. Department of Agriculture defines climate zones according to the lowest average temperature in the region. You may also be familiar with the 24 climate zones identified in Sunset Magazine’s iconic Sunset Western Garden Book. The book is now out of print, but is available online as an interactive edition. Existing print copies from the last edition printed in 2012 are prized heirlooms.

Devoted gardeners still follow the 24 climate zones featured in the guide. This is based on the California Irrigation Management Information System (CIMIS) adoption of a similar map identifying 24 climate zones.

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

Evaporation + Transpiration = Evapotranspiration

Depending on the amount of rainfall, temperature, humidity, wind, shade, and the nature of the soil, water in the ground evaporates at different rates. When evaporation is higher, the soil becomes dry more quickly.

Evapotranspiration (ET) is the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces, and by transpiration from plants.

Reference Evapotranspiration (ETo) is a baseline formula. All your plant water needs are measured against this baseline in a complex series of measurements and calculations.

Why is understanding evapotranspiration important?

In metropolitan San Diego County, our annual ETo rate increases as you move inland, meaning the soil becomes dry more quickly.

Fortunately, we don’t need to worry about making these calculations on our own. CIMIS maintains a statewide system of weather stations and reference plots. From these, it has identified the six main ET Zones in San Diego County.

Understanding your ETo zone and gardening climate zone are important first steps toward deciding how much water your landscaping will need. Working against the ETo and gardening climate zones can greatly increase your need for irrigation.

Learn more about your ETo climate zone’s specifics and gardening 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 available at SustainableLandscapesSD.org. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

OpenET: Transforming Water Management in the U.S. West With NASA Data

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Building upon more than two decades of research, a new web-based platform called OpenET will soon be putting NASA data in the hands of farmers, water managers and conservation groups to accelerate improvements and innovations in water management. OpenET uses publicly available data and open source models to provide satellite-based information on evapotranspiration (the “ET” in OpenET) in areas as small as a quarter of an acre and at daily, monthly and yearly intervals.

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

Evapotranspiration: The Key To Watering Your Plants

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How much water do plants really need in your landscaping?

Evapotranspiration (ET) is the process of assessing various factors to determine how much water plants use, and when they need it. ET is a quick, simple way for landscape experts to explain environmental conditions such as solar radiation (sunshine) or cloud cover. The stronger the sun’s rays, the higher the ET. 

Think of plant leaves as having similar properties to solar panels. They gather energy that enables plants to transform water and carbon dioxide from the air into oxygen and sugars for growing, and for feeding soil microbes. Transpiration of moisture through leaves is a little like people sweating. It cools down the leaves. Water also evaporates from the soil itself around plants. The combined water loss from the plants and the soil together makes up evapotranspiration.  

Why do you need to know this? Understanding water loss in terms of ET is helpful when you select plants for sustainable landscaping, so you choose the lowest Landscape Water Requirements; in planning irrigation; and managing the Soil Moisture Account.  

Look for Four Characteristics Shared By Drought–Tolerant Plants 

Do you need help identifying climate-appropriate plant choices for your new sustainable landscaping? There are four characteristics shared by drought-tolerant plants. 

Stiff, Leathery Leaves: These leaves hold on to water and stay evergreen most of the year. 

Silver or Hairy Leaves: Light colored leaves reflect sunlight, cooling the plant. Hairy leaves hold moisture longer and keep the plant cooled off. 

Tiny Leaves: These are like tiny solar panels, easier to keep cool than one large hot surface. 

Solar Tracking Leaves: These leaves seem to stand at attention in the middle of the day, straight up and down. As the day progresses, the leaves become more horizontal as the plant shifts its solar panel leaves to minimize sun exposure. Many California native plants like manzanitas have this ingenious adaptation.  

The Water Authority’s Sustainable Landscaping guidebook contains a Plant List with climate-appropriate plants. They are also highlighted throughout the guidebook. 

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