Plant Watering Guide
How much water do your plants need?
Depending on the size and type of the plant (tree, shrub, or groundcover), you will need to water to different depths and widths. A large tree needs more water than a small groundcover because it has a larger root zone—the area in which the plant’s feeder roots are concentrated. Your plants will be healthiest if you completely wet the root zone each time you water.
The 1-2-3 Rule is an easy way to remember how deep to water
Water small plants such as groundcovers, cacti, and annuals to a depth of 1 foot. (Grass should be watered to a depth of 10 inches.)
Water medium plants such as shrubs to a depth of 2 feet.
Water large plants such as trees to a depth of 3 feet.
Test how much you’ve watered
A good way to test how deep you have watered is to use a soil probe—a sharpened piece of rebar or a very long screwdriver works well.
About an hour after watering, push the probe into the soil. It will slide easily through wet soil but will be difficult or impossible to push through dry soil. Water your plants and lawn until you can easily slide the probe to the recommended depth.
How wide should you water?
After plants are established, most water-absorbing roots are located near the dripline—which is beneath the outer edge of the plant’s canopy—not close to the trunk or stem.
Concentrate your emitters along the dripline of each plant. The water will spread down and horizontally as it soaks into the soil, reaching the entire root zone.
How much water does each part of your watering system apply?
Now that you have an idea of how much water your plants need, you need to find out how much water your irrigation system applies.
Measuring drip or bubbler output
Drip emitters are typically used around trees and shrubs and are sized in gallons or liters per hour. If you have more than one emitter on a plant (and you often should), total the output of the emitters on each plant. For example, if your tree has three 2-gallon per hour emitters, the output will be 3 emitters x 2 gallons = 6 gallons per hour.
If you don’t know the output of your drip emitters, you can remove an emitter and take it to an irrigation supply or home and garden store, or you can estimate emitter output using the diagram below.
Bubblers typically apply 1/2 to 2 gallons per minute. Some allow you to adjust the flow and some do not. The flow rate is often stamped on the top of the bubbler.
Now you’re ready to calculate the total emitter output for your plants. This output will help determine run times for each watering line or valve. It is not necessary to list every plant in your landscape. You can group them by type and size, such as 15-foot trees, 6-foot shrubs, or 3-foot groundcovers (sizes refer to the diameter of the plant canopy).
Enter your measurements and get a watering schedule
Input the measurements from your worksheet to estimate the run time for each area of your landscape.
If you have bubblers that are measured in Gallons per Minute, multiply this number by 60 to get the Gallons per Hour. Example: 1 Gallon per Minute equals 60 Gallons per Hour.
Your Plant Watering Schedule
- Please enter a complete set of information for each valve.
- The valve on line #1 requires a very short run time.
- The valve on line #2 requires a very long run time.
To improve the efficiency of your watering system, adjust the number and output of emitters on each plant so that they get the total quantity of water they need in two to six hours. For example, a tree with a five-foot canopy needs about 22 gallons of water around its root zone. If you had a single 1-gallon per hour emitter on this tree, you would need to water for 22 hours. Clearly, an adjustment to this emitter system would be needed. A good setup for a five-foot tree would be three 2-gallon per hour emitters spread out around the dripline of the tree. At a combined output of 6 gallons per hour, the tree would get a healthy drink in about 3.5 hours.
- The recommended run times for plants on valve 1 differ by more than 30 minutes.
There is too large a difference in the recommended run times for plants on one or more of your valves. Using the suggested number of emitters from the chart to the right, you can adjust the number of emitters and/or the emitter output rates on different plants to bring the watering times in line with one another
As weather and other factors change, you will need to adjust your watering frequency, not the run time.
The Landscape Watering Guidelines below is divided into seasons. It is important to adjust your watering schedule at least seasonally, because plants can use 3 to 5 times as much water during the hot, dry summer as they do during winter.
These guidelines are for established plants (1 year for shrubs, 3 years for trees). Additional water is needed for new plantings or unusually hot or dry weather. Less water is needed during cool or rainy weather. Drip run times are typically 2 hours or more for each watering.