Three Truths For Water Management
Weather information beyond temperature and simple devices like rain sensors are critical for precise irrigation management. Plant scientists teach us to balance the amount of water depleting from the landscape due to weather, the amount of water applied via irrigation, and free water from the heavens (rainfall!). Keeping the balance is key to minimizing water use and ensuring your plant and landscape assets are healthy and happy. Once you know the inches of water a plant needs to be healthy, the inches of water depleting from the landscape, and the inches of water applied by irrigation and rainfall, you can dial in precise watering control. You can’t do this without weather data gathered, analyzed, and distributed automatically.
Truth 1 – Different plants use water at different rates.
Knowing how much water your plant needs is key to proper water management. There are many places to learn the water requirement of plants. Knowing the plant’s water requirement and the evapotranspiration for the day is the first step of precision water management.
The easiest way to understand evapotranspiration is to think the opposite of rain. ET is the amount of water that evaporates from the soil and plant surface plus transpiration through the plant. Temperature, solar radiation, humidity, and wind velocity all affect ET daily. Knowing when plants need water and knowing when they are full is the first step to a healthy, thriving landscape. ET is almost always discussed in terms of a reference crop, alfalfa, or grass. When reported, today’s ET was .2, or this week’s ET was 1 inch consider this is for alfalfa ETr or grass ETo. The plants in our landscapes may need more or less water depending on several factors, one important factor being the plant species.
Reference ET is a measurement of water use for a specific grass or crop. The plants in your landscape mostly have different water requirements than alfalfa or grass. This is where the plant species factor becomes essential. Knowing your plant species factor allows watering for a specific plant. By multiplying the reference ET by the plant factor, we determine the specific plant’s water requirement. Here is a link to a site that has the most comprehensive database of plant factors for California landscapes
Truth 2 – If you use a standard sprinkler timer, most likely, you are overwatering.
Intuitively when we see a plant not doing well, we give the plant more water. Often this is the incorrect thing to do. When we don’t know how much water is in the soil, we overwater because we don’t want the plant to run dry. If it runs dry, we kill it immediately. If we overwater, we probably kill it slowly over time. If you drive a car without a gas gauge, you will most likely fill up the tank too often because you know if you run out of gas, you have a real problem.
ETwater smart controllers using Jain Unity software set up an irrigation schedule for you. Using many factors, including how much water your plants use, soil type, wind, solar radiation, temperature, shade, slopes, and cloud cover, to name a few. Once the schedule is scientifically established, it is adjusted daily based on ET’s hourly calculation specific to the controller site. No wild guesses, pure science.
Truth 3 – Rainfall is money.
To maximize savings, evaluate rainfall two ways. First, actual rain is based on how much of the rain is useable. If the average rainfall is 10 inches a year and it rains 9 inches in one day, most of the water is not used by plants. It runs off the landscape or pushes past roots in the soil. It’s good to get rain, but often only a fraction of the rain is usable. Jain Unity software measures effective rainfall and enters the amount into your water calculation and schedule. Also, Jain Unity using predictive analytics to adjust your watering schedule based on future weather and rain. Why water a half-inch today if you are going to receive a quarter-inch of rain tomorrow. Unity will reduce the water today, evaluate tomorrow how much rain was usable and schedule the next irrigation accordingly. Using a standard sprinkler configuration costs around $10K a year in Northern California to water an acre of turf. In Southern California, the number is around $17K a year. Using a controller that calculates rainfall and future ET is a huge money saver.
The three truths are not magic. Plants need different amounts of water, and the amounts are known. We measure ET to know how much water the plant needs to replace. Finally, use rain to supplement your irrigation and save money. This is most efficiently done using a smart controller. Considering the water cost today and many water agencies are offering rebates for smart controllers, the time to make the switch is now.