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You installation of a drip irrigation system and now you are wondering how long to set the timer for? It’s a common struggle for gardeners because the short answer is: It depends.
But if I had to make an educated recommendation, I’d say: Start with 40 minutes, observe and adjust.
However, there is a lot more to it, and observation and adjustment are key to making sure your plants are getting enough water.
You’ll find plenty of other basic suggestions online, but the truth is, how long (and how often) your drip irrigation system will run depends on several factors:
- Emissions dimension
- Emission flow rate
- Water pressure
- Size and type of plant being watered
- Ground texture
- Climate (temperature, wind, rain, etc.)
So calculating it exact The time you need to run the drip irrigation is not possible, but you can get pretty close with my interactive Runtime calculator (below).
I designed the calculator to help you determine how much water your garden needs and how long it takes drip irrigation to deliver that amount. It’s not a perfect calculation because it doesn’t take into account your soil type or climate, but you can use the suggested run time as a starting point.
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Drip Irrigation Runtime Calculator
How to use this tool
Our drip irrigation calculator gives you an approximate run time per watering period.
You will need to know three things to determine the runtime:
- Irrigation Areameasured in square feet
- Water depthmeasured in inches
- Area flow ratemeasured in gallons per hour (GPH)
Irrigation area
Irrigation area is the size of the zone being watered, which can be raised beds, in-ground garden beds, or even container gardens.
Calculate the irrigation area by multiplying the length by the width.
Water depth
Water depth is the desired amount of water infiltration per week. If you grow vegetables, the usual rule of thumb is to start with 1 inch of water per weekbut the actual amount depends on climate, soil type, sun exposure and plant maturity.
Use the chart below for a general guideline of how many inches of water your plants may need per week. Divide this number by the number of watering times each week to determine the “water depth” for the calculator.
Pro Tip: If your soil is sandy or your garden gets full sun, follow this higher end of water area. If your soil is clay or your garden is partially shaded, go with it lower end.
|
Plant type |
Cool Climate (inches/week) |
Moderate Climate (inches/week) |
Hot/dry climate (inches/week) |
|---|---|---|---|
|
Vegetables |
1 – 1.5 |
1.25 – 1.75 |
1.5 – 2+ |
|
Flowers |
0.75 – 1 |
1 – 1.5 |
1.25 – 1.75 |
|
Shrubs |
0.5 – 0.75 |
0.75 – 1.25 |
1 – 1.5 |
|
Trees (established) |
0.5 – 1 |
0.75 – 1.25 |
1 – 1.5 |
Area flow rate
The area flow rate is the sum of the flow rates of all emissions in the irrigated area. The flow rate is usually printed on the transmitter or package and looks like 0.5 GPH, 1 GPH, 2 GPH, etc.
Note that flow rates vary with water pressure (psi). The specs of this transmitter should either tell you what psi the flow rate is referenced to, or give you a range of flow rates at 10 psi, 20 psi, 30 psi, and so on.
Most drip irrigation systems require a pressure regulator to ensure that the water pressure is low enough for proper operation (typically 20 to 30 psi). You will get a more accurate calculation if you know the psi of your system.
To determine the area flow rate, count the number of emitters in that area and multiply by the flow rate per emitter (GPH).
Calculation example
Let’s say your garden bed is 4 feet wide and 8 feet long, so 4 x 8 = 32 square feet.
The water depth required for your vegetables is 1.5 inches per week. Your plants are still small and need watering three times a week, so 1.5 ÷ 3 = 0.5 inch.
You have 4 drips in the bed and each line has 12 emitters, so 5 x 12 = 60 emitters.
Each emitter has a flow rate of 1 GPH, so 1 x 60 = 60 GPH.
If you plug these bold figures into the calculator, you will find that you need to use the drip irrigation system for 10 minutes (three times a week).
In the example above, I only calculated the run time for a single 4×8 garden bed, but you can calculate for an entire garden area the same way.
Observe and adjust
Remember what I said earlier about observation and adaptation? The runtime is just a jump.
Let’s use the above example where you water seedlings three times a week for 10 minutes each time. As your plants grow and their roots go deeper, you may want to change the watering just once a week for 30 minutes.
Then, as the weather gets warmer in the summer, your plants may need 2 inches of water each week, which equates to 40 minutes of run time. You can deliver this amount in one session or water twice a week.
Shallower-rooted plants (like lettuce) benefit from more frequent watering in shorter bursts, while deeper-rooted plants (like tomatoes) prefer longer but less frequent watering.
The only way to know if you are giving your plants enough water is to test the soil after the recommended watering time. Scrape down into the soil and see how wet it is an inch down. this is the only depth where it starts to count because you can’t tell if you’ve watered enough just by looking at the surface of the soil.
The next day dig and see how much water has penetrated. If it is much deeper than the roots of the plants, you can reduce the run time or extend the interval between watering periods.
You can also judge your garden’s water needs by paying attention to your plants. Let’s say you want to take it easy and use my recommendation of 40 minutes as the run time.
After two or three days, do you notice wilting in the late afternoon or evening? Then increase the run time to 50 minutes or decrease the interval (from three days to two days) and see if it makes a difference. Or if the soil surface still looks wet after a few days, wait to run the drip irrigation again.
I often play around with my watering schedule in the summer, based on what I’m growing and what the weather is doing.
For reference, my garden is in a dry, high desert climate in Oregon. I use drip tape in 2 foot deep raised beds with clay soil and full south exposure all day.
In the height of summer, I usually drip-irrigate vegetables for about 30 minutes every other day and adjust up or down as needed. As my cucumbers and tomatoes grow, I might set the timer for 45 minutes every three days.
That’s why I recommend starting with a 40-minute baseline if you don’t know your flow rates or don’t want to bother with the calculations. Know your soil, observe your plants and remember that watering times should change with the seasons.
